Simplify type aliasing somewhat around times

[rust-lightning] / lightning / src / routing / scoring.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Utilities for scoring payment channels.
//!
//! [`ProbabilisticScorer`] may be given to [`find_route`] to score payment channels during path
//! finding when a custom [`Score`] implementation is not needed.
//!
//! # Example
//!
//! ```
//! # extern crate secp256k1;
//! #
//! # use lightning::routing::network_graph::NetworkGraph;
//! # use lightning::routing::router::{RouteParameters, find_route};
//! # use lightning::routing::scoring::{ProbabilisticScorer, ProbabilisticScoringParameters, Scorer, ScoringParameters};
//! # use lightning::chain::keysinterface::{KeysManager, KeysInterface};
//! # use lightning::util::logger::{Logger, Record};
//! # use secp256k1::key::PublicKey;
//! #
//! # struct FakeLogger {};
//! # impl Logger for FakeLogger {
//! #     fn log(&self, record: &Record) { unimplemented!() }
//! # }
//! # fn find_scored_route(payer: PublicKey, route_params: RouteParameters, network_graph: NetworkGraph) {
//! # let logger = FakeLogger {};
//! #
//! // Use the default channel penalties.
//! let params = ProbabilisticScoringParameters::default();
//! let scorer = ProbabilisticScorer::new(params, &network_graph);
//!
//! // Or use custom channel penalties.
//! let params = ProbabilisticScoringParameters {
//!     liquidity_penalty_multiplier_msat: 2 * 1000,
//!     ..ProbabilisticScoringParameters::default()
//! };
//! let scorer = ProbabilisticScorer::new(params, &network_graph);
//! # let random_seed_bytes = [42u8; 32];
//!
//! let route = find_route(&payer, &route_params, &network_graph, None, &logger, &scorer, &random_seed_bytes);
//! # }
//! ```
//!
//! # Note
//!
//! Persisting when built with feature `no-std` and restoring without it, or vice versa, uses
//! different types and thus is undefined.
//!
//! [`find_route`]: crate::routing::router::find_route

use ln::msgs::DecodeError;
use routing::network_graph::{NetworkGraph, NodeId};
use routing::router::RouteHop;
use util::ser::{Readable, ReadableArgs, Writeable, Writer};

use prelude::*;
use core::cell::{RefCell, RefMut};
use core::ops::{Deref, DerefMut};
use core::time::Duration;
use io::{self, Read};
use sync::{Mutex, MutexGuard};

/// We define Score ever-so-slightly differently based on whether we are being built for C bindings
/// or not. For users, `LockableScore` must somehow be writeable to disk. For Rust users, this is
/// no problem - you move a `Score` that implements `Writeable` into a `Mutex`, lock it, and now
/// you have the original, concrete, `Score` type, which presumably implements `Writeable`.
///
/// For C users, once you've moved the `Score` into a `LockableScore` all you have after locking it
/// is an opaque trait object with an opaque pointer with no type info. Users could take the unsafe
/// approach of blindly casting that opaque pointer to a concrete type and calling `Writeable` from
/// there, but other languages downstream of the C bindings (e.g. Java) can't even do that.
/// Instead, we really want `Score` and `LockableScore` to implement `Writeable` directly, which we
/// do here by defining `Score` differently for `cfg(c_bindings)`.
macro_rules! define_score { ($($supertrait: path)*) => {
/// An interface used to score payment channels for path finding.
///
///     Scoring is in terms of fees willing to be paid in order to avoid routing through a channel.
pub trait Score $(: $supertrait)* {
        /// Returns the fee in msats willing to be paid to avoid routing `send_amt_msat` through the
        /// given channel in the direction from `source` to `target`.
        ///
        /// The channel's capacity (less any other MPP parts that are also being considered for use in
        /// the same payment) is given by `capacity_msat`. It may be determined from various sources
        /// such as a chain data, network gossip, or invoice hints. For invoice hints, a capacity near
        /// [`u64::max_value`] is given to indicate sufficient capacity for the invoice's full amount.
        /// Thus, implementations should be overflow-safe.
        fn channel_penalty_msat(&self, short_channel_id: u64, send_amt_msat: u64, capacity_msat: u64, source: &NodeId, target: &NodeId) -> u64;

        /// Handles updating channel penalties after failing to route through a channel.
        fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64);

        /// Handles updating channel penalties after successfully routing along a path.
        fn payment_path_successful(&mut self, path: &[&RouteHop]);
}

impl<S: Score, T: DerefMut<Target=S> $(+ $supertrait)*> Score for T {
        fn channel_penalty_msat(&self, short_channel_id: u64, send_amt_msat: u64, capacity_msat: u64, source: &NodeId, target: &NodeId) -> u64 {
                self.deref().channel_penalty_msat(short_channel_id, send_amt_msat, capacity_msat, source, target)
        }

        fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
                self.deref_mut().payment_path_failed(path, short_channel_id)
        }

        fn payment_path_successful(&mut self, path: &[&RouteHop]) {
                self.deref_mut().payment_path_successful(path)
        }
}
} }

#[cfg(c_bindings)]
define_score!(Writeable);
#[cfg(not(c_bindings))]
define_score!();

/// A scorer that is accessed under a lock.
///
/// Needed so that calls to [`Score::channel_penalty_msat`] in [`find_route`] can be made while
/// having shared ownership of a scorer but without requiring internal locking in [`Score`]
/// implementations. Internal locking would be detrimental to route finding performance and could
/// result in [`Score::channel_penalty_msat`] returning a different value for the same channel.
///
/// [`find_route`]: crate::routing::router::find_route
pub trait LockableScore<'a> {
        /// The locked [`Score`] type.
        type Locked: 'a + Score;

        /// Returns the locked scorer.
        fn lock(&'a self) -> Self::Locked;
}

/// (C-not exported)
impl<'a, T: 'a + Score> LockableScore<'a> for Mutex<T> {
        type Locked = MutexGuard<'a, T>;

        fn lock(&'a self) -> MutexGuard<'a, T> {
                Mutex::lock(self).unwrap()
        }
}

impl<'a, T: 'a + Score> LockableScore<'a> for RefCell<T> {
        type Locked = RefMut<'a, T>;

        fn lock(&'a self) -> RefMut<'a, T> {
                self.borrow_mut()
        }
}

#[cfg(c_bindings)]
/// A concrete implementation of [`LockableScore`] which supports multi-threading.
pub struct MultiThreadedLockableScore<S: Score> {
        score: Mutex<S>,
}
#[cfg(c_bindings)]
/// (C-not exported)
impl<'a, T: Score + 'a> LockableScore<'a> for MultiThreadedLockableScore<T> {
        type Locked = MutexGuard<'a, T>;

        fn lock(&'a self) -> MutexGuard<'a, T> {
                Mutex::lock(&self.score).unwrap()
        }
}

#[cfg(c_bindings)]
impl<T: Score> MultiThreadedLockableScore<T> {
        /// Creates a new [`MultiThreadedLockableScore`] given an underlying [`Score`].
        pub fn new(score: T) -> Self {
                MultiThreadedLockableScore { score: Mutex::new(score) }
        }
}

#[cfg(c_bindings)]
/// (C-not exported)
impl<'a, T: Writeable> Writeable for RefMut<'a, T> {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
                T::write(&**self, writer)
        }
}

#[cfg(c_bindings)]
/// (C-not exported)
impl<'a, S: Writeable> Writeable for MutexGuard<'a, S> {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
                S::write(&**self, writer)
        }
}

#[derive(Clone)]
/// [`Score`] implementation that uses a fixed penalty.
pub struct FixedPenaltyScorer {
        penalty_msat: u64,
}

impl FixedPenaltyScorer {
        /// Creates a new scorer using `penalty_msat`.
        pub fn with_penalty(penalty_msat: u64) -> Self {
                Self { penalty_msat }
        }
}

impl Score for FixedPenaltyScorer {
        fn channel_penalty_msat(&self, _: u64, _: u64, _: u64, _: &NodeId, _: &NodeId) -> u64 {
                self.penalty_msat
        }

        fn payment_path_failed(&mut self, _path: &[&RouteHop], _short_channel_id: u64) {}

        fn payment_path_successful(&mut self, _path: &[&RouteHop]) {}
}

impl Writeable for FixedPenaltyScorer {
        #[inline]
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
                write_tlv_fields!(w, {});
                Ok(())
        }
}

impl ReadableArgs<u64> for FixedPenaltyScorer {
        #[inline]
        fn read<R: Read>(r: &mut R, penalty_msat: u64) -> Result<Self, DecodeError> {
                read_tlv_fields!(r, {});
                Ok(Self { penalty_msat })
        }
}

/// [`Score`] implementation that provides reasonable default behavior.
///
/// Used to apply a fixed penalty to each channel, thus avoiding long paths when shorter paths with
/// slightly higher fees are available. Will further penalize channels that fail to relay payments.
///
/// See [module-level documentation] for usage and [`ScoringParameters`] for customization.
///
/// # Note
///
/// Mixing the `no-std` feature between serialization and deserialization results in undefined
/// behavior.
///
/// [module-level documentation]: crate::routing::scoring
#[deprecated(
        since = "0.0.105",
        note = "ProbabilisticScorer should be used instead of Scorer.",
)]
#[cfg(not(feature = "no-std"))]
pub type Scorer = ScorerUsingTime::<std::time::Instant>;
#[cfg(feature = "no-std")]
pub type Scorer = ScorerUsingTime::<time::Eternity>;

// Note that ideally we'd hide ScorerUsingTime from public view by sealing it as well, but rustdoc
// doesn't handle this well - instead exposing a `Scorer` which has no trait implementation(s) or
// methods at all.

/// [`Score`] implementation.
///
/// (C-not exported) generally all users should use the [`Scorer`] type alias.
pub struct ScorerUsingTime<T: Time> {
        params: ScoringParameters,
        // TODO: Remove entries of closed channels.
        channel_failures: HashMap<u64, ChannelFailure<T>>,
}

#[derive(Clone)]
/// Parameters for configuring [`Scorer`].
pub struct ScoringParameters {
        /// A fixed penalty in msats to apply to each channel.
        ///
        /// Default value: 500 msat
        pub base_penalty_msat: u64,

        /// A penalty in msats to apply to a channel upon failing to relay a payment.
        ///
        /// This accumulates for each failure but may be reduced over time based on
        /// [`failure_penalty_half_life`] or when successfully routing through a channel.
        ///
        /// Default value: 1,024,000 msat
        ///
        /// [`failure_penalty_half_life`]: Self::failure_penalty_half_life
        pub failure_penalty_msat: u64,

        /// When the amount being sent over a channel is this many 1024ths of the total channel
        /// capacity, we begin applying [`overuse_penalty_msat_per_1024th`].
        ///
        /// Default value: 128 1024ths (i.e. begin penalizing when an HTLC uses 1/8th of a channel)
        ///
        /// [`overuse_penalty_msat_per_1024th`]: Self::overuse_penalty_msat_per_1024th
        pub overuse_penalty_start_1024th: u16,

        /// A penalty applied, per whole 1024ths of the channel capacity which the amount being sent
        /// over the channel exceeds [`overuse_penalty_start_1024th`] by.
        ///
        /// Default value: 20 msat (i.e. 2560 msat penalty to use 1/4th of a channel, 7680 msat penalty
        ///                to use half a channel, and 12,560 msat penalty to use 3/4ths of a channel)
        ///
        /// [`overuse_penalty_start_1024th`]: Self::overuse_penalty_start_1024th
        pub overuse_penalty_msat_per_1024th: u64,

        /// The time required to elapse before any accumulated [`failure_penalty_msat`] penalties are
        /// cut in half.
        ///
        /// Successfully routing through a channel will immediately cut the penalty in half as well.
        ///
        /// Default value: 1 hour
        ///
        /// # Note
        ///
        /// When built with the `no-std` feature, time will never elapse. Therefore, this penalty will
        /// never decay.
        ///
        /// [`failure_penalty_msat`]: Self::failure_penalty_msat
        pub failure_penalty_half_life: Duration,
}

impl_writeable_tlv_based!(ScoringParameters, {
        (0, base_penalty_msat, required),
        (1, overuse_penalty_start_1024th, (default_value, 128)),
        (2, failure_penalty_msat, required),
        (3, overuse_penalty_msat_per_1024th, (default_value, 20)),
        (4, failure_penalty_half_life, required),
});

/// Accounting for penalties against a channel for failing to relay any payments.
///
/// Penalties decay over time, though accumulate as more failures occur.
struct ChannelFailure<T: Time> {
        /// Accumulated penalty in msats for the channel as of `last_updated`.
        undecayed_penalty_msat: u64,

        /// Last time the channel either failed to route or successfully routed a payment. Used to decay
        /// `undecayed_penalty_msat`.
        last_updated: T,
}

impl<T: Time> ScorerUsingTime<T> {
        /// Creates a new scorer using the given scoring parameters.
        pub fn new(params: ScoringParameters) -> Self {
                Self {
                        params,
                        channel_failures: HashMap::new(),
                }
        }
}

impl<T: Time> ChannelFailure<T> {
        fn new(failure_penalty_msat: u64) -> Self {
                Self {
                        undecayed_penalty_msat: failure_penalty_msat,
                        last_updated: T::now(),
                }
        }

        fn add_penalty(&mut self, failure_penalty_msat: u64, half_life: Duration) {
                self.undecayed_penalty_msat = self.decayed_penalty_msat(half_life) + failure_penalty_msat;
                self.last_updated = T::now();
        }

        fn reduce_penalty(&mut self, half_life: Duration) {
                self.undecayed_penalty_msat = self.decayed_penalty_msat(half_life) >> 1;
                self.last_updated = T::now();
        }

        fn decayed_penalty_msat(&self, half_life: Duration) -> u64 {
                self.last_updated.elapsed().as_secs()
                        .checked_div(half_life.as_secs())
                        .and_then(|decays| self.undecayed_penalty_msat.checked_shr(decays as u32))
                        .unwrap_or(0)
        }
}

impl<T: Time> Default for ScorerUsingTime<T> {
        fn default() -> Self {
                Self::new(ScoringParameters::default())
        }
}

impl Default for ScoringParameters {
        fn default() -> Self {
                Self {
                        base_penalty_msat: 500,
                        failure_penalty_msat: 1024 * 1000,
                        failure_penalty_half_life: Duration::from_secs(3600),
                        overuse_penalty_start_1024th: 1024 / 8,
                        overuse_penalty_msat_per_1024th: 20,
                }
        }
}

impl<T: Time> Score for ScorerUsingTime<T> {
        fn channel_penalty_msat(
                &self, short_channel_id: u64, send_amt_msat: u64, capacity_msat: u64, _source: &NodeId, _target: &NodeId
        ) -> u64 {
                let failure_penalty_msat = self.channel_failures
                        .get(&short_channel_id)
                        .map_or(0, |value| value.decayed_penalty_msat(self.params.failure_penalty_half_life));

                let mut penalty_msat = self.params.base_penalty_msat + failure_penalty_msat;
                let send_1024ths = send_amt_msat.checked_mul(1024).unwrap_or(u64::max_value()) / capacity_msat;
                if send_1024ths > self.params.overuse_penalty_start_1024th as u64 {
                        penalty_msat = penalty_msat.checked_add(
                                        (send_1024ths - self.params.overuse_penalty_start_1024th as u64)
                                        .checked_mul(self.params.overuse_penalty_msat_per_1024th).unwrap_or(u64::max_value()))
                                .unwrap_or(u64::max_value());
                }

                penalty_msat
        }

        fn payment_path_failed(&mut self, _path: &[&RouteHop], short_channel_id: u64) {
                let failure_penalty_msat = self.params.failure_penalty_msat;
                let half_life = self.params.failure_penalty_half_life;
                self.channel_failures
                        .entry(short_channel_id)
                        .and_modify(|failure| failure.add_penalty(failure_penalty_msat, half_life))
                        .or_insert_with(|| ChannelFailure::new(failure_penalty_msat));
        }

        fn payment_path_successful(&mut self, path: &[&RouteHop]) {
                let half_life = self.params.failure_penalty_half_life;
                for hop in path.iter() {
                        self.channel_failures
                                .entry(hop.short_channel_id)
                                .and_modify(|failure| failure.reduce_penalty(half_life));
                }
        }
}

impl<T: Time> Writeable for ScorerUsingTime<T> {
        #[inline]
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
                self.params.write(w)?;
                self.channel_failures.write(w)?;
                write_tlv_fields!(w, {});
                Ok(())
        }
}

impl<T: Time> Readable for ScorerUsingTime<T> {
        #[inline]
        fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
                let res = Ok(Self {
                        params: Readable::read(r)?,
                        channel_failures: Readable::read(r)?,
                });
                read_tlv_fields!(r, {});
                res
        }
}

impl<T: Time> Writeable for ChannelFailure<T> {
        #[inline]
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
                let duration_since_epoch = T::duration_since_epoch() - self.last_updated.elapsed();
                write_tlv_fields!(w, {
                        (0, self.undecayed_penalty_msat, required),
                        (2, duration_since_epoch, required),
                });
                Ok(())
        }
}

impl<T: Time> Readable for ChannelFailure<T> {
        #[inline]
        fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
                let mut undecayed_penalty_msat = 0;
                let mut duration_since_epoch = Duration::from_secs(0);
                read_tlv_fields!(r, {
                        (0, undecayed_penalty_msat, required),
                        (2, duration_since_epoch, required),
                });
                Ok(Self {
                        undecayed_penalty_msat,
                        last_updated: T::now() - (T::duration_since_epoch() - duration_since_epoch),
                })
        }
}

/// [`Score`] implementation using channel success probability distributions.
///
/// Based on *Optimally Reliable & Cheap Payment Flows on the Lightning Network* by Rene Pickhardt
/// and Stefan Richter [[1]]. Given the uncertainty of channel liquidity balances, probability
/// distributions are defined based on knowledge learned from successful and unsuccessful attempts.
/// Then the negative `log10` of the success probability is used to determine the cost of routing a
/// specific HTLC amount through a channel.
///
/// Knowledge about channel liquidity balances takes the form of upper and lower bounds on the
/// possible liquidity. Certainty of the bounds is decreased over time using a decay function. See
/// [`ProbabilisticScoringParameters`] for details.
///
/// Since the scorer aims to learn the current channel liquidity balances, it works best for nodes
/// with high payment volume or that actively probe the [`NetworkGraph`]. Nodes with low payment
/// volume are more likely to experience failed payment paths, which would need to be retried.
///
/// # Note
///
/// Mixing the `no-std` feature between serialization and deserialization results in undefined
/// behavior.
///
/// [1]: https://arxiv.org/abs/2107.05322
#[cfg(not(feature = "no-std"))]
pub type ProbabilisticScorer<G> = ProbabilisticScorerUsingTime::<G, std::time::Instant>;
#[cfg(feature = "no-std")]
pub type ProbabilisticScorer<G> = ProbabilisticScorerUsingTime::<G, time::Eternity>;

/// Probabilistic [`Score`] implementation.
///
/// (C-not exported) generally all users should use the [`ProbabilisticScorer`] type alias.
pub struct ProbabilisticScorerUsingTime<G: Deref<Target = NetworkGraph>, T: Time> {
        params: ProbabilisticScoringParameters,
        network_graph: G,
        // TODO: Remove entries of closed channels.
        channel_liquidities: HashMap<u64, ChannelLiquidity<T>>,
}

/// Parameters for configuring [`ProbabilisticScorer`].
///
/// Used to configure base, liquidity, and amount penalties, the sum of which comprises the channel
/// penalty (i.e., the amount in msats willing to be paid to avoid routing through the channel).
#[derive(Clone, Copy)]
pub struct ProbabilisticScoringParameters {
        /// A fixed penalty in msats to apply to each channel.
        ///
        /// Default value: 500 msat
        pub base_penalty_msat: u64,

        /// A multiplier used in conjunction with the negative `log10` of the channel's success
        /// probability for a payment to determine the liquidity penalty.
        ///
        /// The penalty is based in part on the knowledge learned from prior successful and unsuccessful
        /// payments. This knowledge is decayed over time based on [`liquidity_offset_half_life`]. The
        /// penalty is effectively limited to `2 * liquidity_penalty_multiplier_msat` (corresponding to
        /// lower bounding the success probability to `0.01`) when the amount falls within the
        /// uncertainty bounds of the channel liquidity balance. Amounts above the upper bound will
        /// result in a `u64::max_value` penalty, however.
        ///
        /// Default value: 40,000 msat
        ///
        /// [`liquidity_offset_half_life`]: Self::liquidity_offset_half_life
        pub liquidity_penalty_multiplier_msat: u64,

        /// The time required to elapse before any knowledge learned about channel liquidity balances is
        /// cut in half.
        ///
        /// The bounds are defined in terms of offsets and are initially zero. Increasing the offsets
        /// gives tighter bounds on the channel liquidity balance. Thus, halving the offsets decreases
        /// the certainty of the channel liquidity balance.
        ///
        /// Default value: 1 hour
        ///
        /// # Note
        ///
        /// When built with the `no-std` feature, time will never elapse. Therefore, the channel
        /// liquidity knowledge will never decay except when the bounds cross.
        pub liquidity_offset_half_life: Duration,

        /// A multiplier used in conjunction with a payment amount and the negative `log10` of the
        /// channel's success probability for the payment to determine the amount penalty.
        ///
        /// The purpose of the amount penalty is to avoid having fees dominate the channel cost (i.e.,
        /// fees plus penalty) for large payments. The penalty is computed as the product of this
        /// multiplier and `2^20`ths of the payment amount, weighted by the negative `log10` of the
        /// success probability.
        ///
        /// `-log10(success_probability) * amount_penalty_multiplier_msat * amount_msat / 2^20`
        ///
        /// In practice, this means for 0.1 success probability (`-log10(0.1) == 1`) each `2^20`th of
        /// the amount will result in a penalty of the multiplier. And, as the success probability
        /// decreases, the negative `log10` weighting will increase dramatically. For higher success
        /// probabilities, the multiplier will have a decreasing effect as the negative `log10` will
        /// fall below `1`.
        ///
        /// Default value: 256 msat
        pub amount_penalty_multiplier_msat: u64,
}

/// Accounting for channel liquidity balance uncertainty.
///
/// Direction is defined in terms of [`NodeId`] partial ordering, where the source node is the
/// first node in the ordering of the channel's counterparties. Thus, swapping the two liquidity
/// offset fields gives the opposite direction.
struct ChannelLiquidity<T: Time> {
        /// Lower channel liquidity bound in terms of an offset from zero.
        min_liquidity_offset_msat: u64,

        /// Upper channel liquidity bound in terms of an offset from the effective capacity.
        max_liquidity_offset_msat: u64,

        /// Time when the liquidity bounds were last modified.
        last_updated: T,
}

/// A snapshot of [`ChannelLiquidity`] in one direction assuming a certain channel capacity and
/// decayed with a given half life.
struct DirectedChannelLiquidity<L: Deref<Target = u64>, T: Time, U: Deref<Target = T>> {
        min_liquidity_offset_msat: L,
        max_liquidity_offset_msat: L,
        capacity_msat: u64,
        last_updated: U,
        now: T,
        half_life: Duration,
}

impl<G: Deref<Target = NetworkGraph>, T: Time> ProbabilisticScorerUsingTime<G, T> {
        /// Creates a new scorer using the given scoring parameters for sending payments from a node
        /// through a network graph.
        pub fn new(params: ProbabilisticScoringParameters, network_graph: G) -> Self {
                Self {
                        params,
                        network_graph,
                        channel_liquidities: HashMap::new(),
                }
        }

        #[cfg(test)]
        fn with_channel(mut self, short_channel_id: u64, liquidity: ChannelLiquidity<T>) -> Self {
                assert!(self.channel_liquidities.insert(short_channel_id, liquidity).is_none());
                self
        }
}

impl ProbabilisticScoringParameters {
        #[cfg(test)]
        fn zero_penalty() -> Self {
                Self {
                        base_penalty_msat: 0,
                        liquidity_penalty_multiplier_msat: 0,
                        liquidity_offset_half_life: Duration::from_secs(3600),
                        amount_penalty_multiplier_msat: 0,
                }
        }
}

impl Default for ProbabilisticScoringParameters {
        fn default() -> Self {
                Self {
                        base_penalty_msat: 500,
                        liquidity_penalty_multiplier_msat: 40_000,
                        liquidity_offset_half_life: Duration::from_secs(3600),
                        amount_penalty_multiplier_msat: 256,
                }
        }
}

impl<T: Time> ChannelLiquidity<T> {
        #[inline]
        fn new() -> Self {
                Self {
                        min_liquidity_offset_msat: 0,
                        max_liquidity_offset_msat: 0,
                        last_updated: T::now(),
                }
        }

        /// Returns a view of the channel liquidity directed from `source` to `target` assuming
        /// `capacity_msat`.
        fn as_directed(
                &self, source: &NodeId, target: &NodeId, capacity_msat: u64, half_life: Duration
        ) -> DirectedChannelLiquidity<&u64, T, &T> {
                let (min_liquidity_offset_msat, max_liquidity_offset_msat) = if source < target {
                        (&self.min_liquidity_offset_msat, &self.max_liquidity_offset_msat)
                } else {
                        (&self.max_liquidity_offset_msat, &self.min_liquidity_offset_msat)
                };

                DirectedChannelLiquidity {
                        min_liquidity_offset_msat,
                        max_liquidity_offset_msat,
                        capacity_msat,
                        last_updated: &self.last_updated,
                        now: T::now(),
                        half_life,
                }
        }

        /// Returns a mutable view of the channel liquidity directed from `source` to `target` assuming
        /// `capacity_msat`.
        fn as_directed_mut(
                &mut self, source: &NodeId, target: &NodeId, capacity_msat: u64, half_life: Duration
        ) -> DirectedChannelLiquidity<&mut u64, T, &mut T> {
                let (min_liquidity_offset_msat, max_liquidity_offset_msat) = if source < target {
                        (&mut self.min_liquidity_offset_msat, &mut self.max_liquidity_offset_msat)
                } else {
                        (&mut self.max_liquidity_offset_msat, &mut self.min_liquidity_offset_msat)
                };

                DirectedChannelLiquidity {
                        min_liquidity_offset_msat,
                        max_liquidity_offset_msat,
                        capacity_msat,
                        last_updated: &mut self.last_updated,
                        now: T::now(),
                        half_life,
                }
        }
}

/// Bounds `-log10` to avoid excessive liquidity penalties for payments with low success
/// probabilities.
const NEGATIVE_LOG10_UPPER_BOUND: u64 = 2;

/// The divisor used when computing the amount penalty.
const AMOUNT_PENALTY_DIVISOR: u64 = 1 << 20;

impl<L: Deref<Target = u64>, T: Time, U: Deref<Target = T>> DirectedChannelLiquidity<L, T, U> {
        /// Returns a penalty for routing the given HTLC `amount_msat` through the channel in this
        /// direction.
        fn penalty_msat(&self, amount_msat: u64, params: ProbabilisticScoringParameters) -> u64 {
                let max_liquidity_msat = self.max_liquidity_msat();
                let min_liquidity_msat = core::cmp::min(self.min_liquidity_msat(), max_liquidity_msat);
                if amount_msat <= min_liquidity_msat {
                        0
                } else if amount_msat >= max_liquidity_msat {
                        if amount_msat > max_liquidity_msat {
                                u64::max_value()
                        } else if max_liquidity_msat != self.capacity_msat {
                                // Avoid using the failed channel on retry.
                                u64::max_value()
                        } else {
                                // Equivalent to hitting the else clause below with the amount equal to the
                                // effective capacity and without any certainty on the liquidity upper bound.
                                let negative_log10_times_1024 = NEGATIVE_LOG10_UPPER_BOUND * 1024;
                                self.combined_penalty_msat(amount_msat, negative_log10_times_1024, params)
                        }
                } else {
                        let numerator = (max_liquidity_msat - amount_msat).saturating_add(1);
                        let denominator = (max_liquidity_msat - min_liquidity_msat).saturating_add(1);
                        let negative_log10_times_1024 =
                                approx::negative_log10_times_1024(numerator, denominator);
                        self.combined_penalty_msat(amount_msat, negative_log10_times_1024, params)
                }
        }

        /// Computes the liquidity and amount penalties and adds them to the base penalty.
        #[inline(always)]
        fn combined_penalty_msat(
                &self, amount_msat: u64, negative_log10_times_1024: u64,
                params: ProbabilisticScoringParameters
        ) -> u64 {
                let liquidity_penalty_msat = {
                        // Upper bound the liquidity penalty to ensure some channel is selected.
                        let multiplier_msat = params.liquidity_penalty_multiplier_msat;
                        let max_penalty_msat = multiplier_msat.saturating_mul(NEGATIVE_LOG10_UPPER_BOUND);
                        (negative_log10_times_1024.saturating_mul(multiplier_msat) / 1024).min(max_penalty_msat)
                };
                let amount_penalty_msat = negative_log10_times_1024
                        .saturating_mul(params.amount_penalty_multiplier_msat)
                        .saturating_mul(amount_msat) / 1024 / AMOUNT_PENALTY_DIVISOR;

                params.base_penalty_msat
                        .saturating_add(liquidity_penalty_msat)
                        .saturating_add(amount_penalty_msat)
        }

        /// Returns the lower bound of the channel liquidity balance in this direction.
        fn min_liquidity_msat(&self) -> u64 {
                self.decayed_offset_msat(*self.min_liquidity_offset_msat)
        }

        /// Returns the upper bound of the channel liquidity balance in this direction.
        fn max_liquidity_msat(&self) -> u64 {
                self.capacity_msat
                        .checked_sub(self.decayed_offset_msat(*self.max_liquidity_offset_msat))
                        .unwrap_or(0)
        }

        fn decayed_offset_msat(&self, offset_msat: u64) -> u64 {
                self.now.duration_since(*self.last_updated).as_secs()
                        .checked_div(self.half_life.as_secs())
                        .and_then(|decays| offset_msat.checked_shr(decays as u32))
                        .unwrap_or(0)
        }
}

impl<L: DerefMut<Target = u64>, T: Time, U: DerefMut<Target = T>> DirectedChannelLiquidity<L, T, U> {
        /// Adjusts the channel liquidity balance bounds when failing to route `amount_msat`.
        fn failed_at_channel(&mut self, amount_msat: u64) {
                if amount_msat < self.max_liquidity_msat() {
                        self.set_max_liquidity_msat(amount_msat);
                }
        }

        /// Adjusts the channel liquidity balance bounds when failing to route `amount_msat` downstream.
        fn failed_downstream(&mut self, amount_msat: u64) {
                if amount_msat > self.min_liquidity_msat() {
                        self.set_min_liquidity_msat(amount_msat);
                }
        }

        /// Adjusts the channel liquidity balance bounds when successfully routing `amount_msat`.
        fn successful(&mut self, amount_msat: u64) {
                let max_liquidity_msat = self.max_liquidity_msat().checked_sub(amount_msat).unwrap_or(0);
                self.set_max_liquidity_msat(max_liquidity_msat);
        }

        /// Adjusts the lower bound of the channel liquidity balance in this direction.
        fn set_min_liquidity_msat(&mut self, amount_msat: u64) {
                *self.min_liquidity_offset_msat = amount_msat;
                *self.max_liquidity_offset_msat = if amount_msat > self.max_liquidity_msat() {
                        0
                } else {
                        self.decayed_offset_msat(*self.max_liquidity_offset_msat)
                };
                *self.last_updated = self.now;
        }

        /// Adjusts the upper bound of the channel liquidity balance in this direction.
        fn set_max_liquidity_msat(&mut self, amount_msat: u64) {
                *self.max_liquidity_offset_msat = self.capacity_msat.checked_sub(amount_msat).unwrap_or(0);
                *self.min_liquidity_offset_msat = if amount_msat < self.min_liquidity_msat() {
                        0
                } else {
                        self.decayed_offset_msat(*self.min_liquidity_offset_msat)
                };
                *self.last_updated = self.now;
        }
}

impl<G: Deref<Target = NetworkGraph>, T: Time> Score for ProbabilisticScorerUsingTime<G, T> {
        fn channel_penalty_msat(
                &self, short_channel_id: u64, amount_msat: u64, capacity_msat: u64, source: &NodeId,
                target: &NodeId
        ) -> u64 {
                let liquidity_offset_half_life = self.params.liquidity_offset_half_life;
                self.channel_liquidities
                        .get(&short_channel_id)
                        .unwrap_or(&ChannelLiquidity::new())
                        .as_directed(source, target, capacity_msat, liquidity_offset_half_life)
                        .penalty_msat(amount_msat, self.params)
        }

        fn payment_path_failed(&mut self, path: &[&RouteHop], short_channel_id: u64) {
                let amount_msat = path.split_last().map(|(hop, _)| hop.fee_msat).unwrap_or(0);
                let liquidity_offset_half_life = self.params.liquidity_offset_half_life;
                let network_graph = self.network_graph.read_only();
                for hop in path {
                        let target = NodeId::from_pubkey(&hop.pubkey);
                        let channel_directed_from_source = network_graph.channels()
                                .get(&hop.short_channel_id)
                                .and_then(|channel| channel.as_directed_to(&target));

                        // Only score announced channels.
                        if let Some((channel, source)) = channel_directed_from_source {
                                let capacity_msat = channel.effective_capacity().as_msat();
                                if hop.short_channel_id == short_channel_id {
                                        self.channel_liquidities
                                                .entry(hop.short_channel_id)
                                                .or_insert_with(ChannelLiquidity::new)
                                                .as_directed_mut(source, &target, capacity_msat, liquidity_offset_half_life)
                                                .failed_at_channel(amount_msat);
                                        break;
                                }

                                self.channel_liquidities
                                        .entry(hop.short_channel_id)
                                        .or_insert_with(ChannelLiquidity::new)
                                        .as_directed_mut(source, &target, capacity_msat, liquidity_offset_half_life)
                                        .failed_downstream(amount_msat);
                        }
                }
        }

        fn payment_path_successful(&mut self, path: &[&RouteHop]) {
                let amount_msat = path.split_last().map(|(hop, _)| hop.fee_msat).unwrap_or(0);
                let liquidity_offset_half_life = self.params.liquidity_offset_half_life;
                let network_graph = self.network_graph.read_only();
                for hop in path {
                        let target = NodeId::from_pubkey(&hop.pubkey);
                        let channel_directed_from_source = network_graph.channels()
                                .get(&hop.short_channel_id)
                                .and_then(|channel| channel.as_directed_to(&target));

                        // Only score announced channels.
                        if let Some((channel, source)) = channel_directed_from_source {
                                let capacity_msat = channel.effective_capacity().as_msat();
                                self.channel_liquidities
                                        .entry(hop.short_channel_id)
                                        .or_insert_with(ChannelLiquidity::new)
                                        .as_directed_mut(source, &target, capacity_msat, liquidity_offset_half_life)
                                        .successful(amount_msat);
                        }
                }
        }
}

mod approx {
        const BITS: u32 = 64;
        const HIGHEST_BIT: u32 = BITS - 1;
        const LOWER_BITS: u32 = 4;
        const LOWER_BITS_BOUND: u64 = 1 << LOWER_BITS;
        const LOWER_BITMASK: u64 = (1 << LOWER_BITS) - 1;

        /// Look-up table for `log10(x) * 1024` where row `i` is used for each `x` having `i` as the
        /// most significant bit. The next 4 bits of `x`, if applicable, are used for the second index.
        const LOG10_TIMES_1024: [[u16; LOWER_BITS_BOUND as usize]; BITS as usize] = [
                [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
                [308, 308, 308, 308, 308, 308, 308, 308, 489, 489, 489, 489, 489, 489, 489, 489],
                [617, 617, 617, 617, 716, 716, 716, 716, 797, 797, 797, 797, 865, 865, 865, 865],
                [925, 925, 977, 977, 1024, 1024, 1066, 1066, 1105, 1105, 1141, 1141, 1174, 1174, 1204, 1204],
                [1233, 1260, 1285, 1309, 1332, 1354, 1375, 1394, 1413, 1431, 1449, 1466, 1482, 1497, 1513, 1527],
                [1541, 1568, 1594, 1618, 1641, 1662, 1683, 1703, 1722, 1740, 1757, 1774, 1790, 1806, 1821, 1835],
                [1850, 1876, 1902, 1926, 1949, 1970, 1991, 2011, 2030, 2048, 2065, 2082, 2098, 2114, 2129, 2144],
                [2158, 2185, 2210, 2234, 2257, 2279, 2299, 2319, 2338, 2356, 2374, 2390, 2407, 2422, 2437, 2452],
                [2466, 2493, 2518, 2542, 2565, 2587, 2608, 2627, 2646, 2665, 2682, 2699, 2715, 2731, 2746, 2760],
                [2774, 2801, 2827, 2851, 2874, 2895, 2916, 2936, 2955, 2973, 2990, 3007, 3023, 3039, 3054, 3068],
                [3083, 3110, 3135, 3159, 3182, 3203, 3224, 3244, 3263, 3281, 3298, 3315, 3331, 3347, 3362, 3377],
                [3391, 3418, 3443, 3467, 3490, 3512, 3532, 3552, 3571, 3589, 3607, 3623, 3640, 3655, 3670, 3685],
                [3699, 3726, 3751, 3775, 3798, 3820, 3841, 3860, 3879, 3898, 3915, 3932, 3948, 3964, 3979, 3993],
                [4007, 4034, 4060, 4084, 4107, 4128, 4149, 4169, 4188, 4206, 4223, 4240, 4256, 4272, 4287, 4301],
                [4316, 4343, 4368, 4392, 4415, 4436, 4457, 4477, 4496, 4514, 4531, 4548, 4564, 4580, 4595, 4610],
                [4624, 4651, 4676, 4700, 4723, 4745, 4765, 4785, 4804, 4822, 4840, 4857, 4873, 4888, 4903, 4918],
                [4932, 4959, 4984, 5009, 5031, 5053, 5074, 5093, 5112, 5131, 5148, 5165, 5181, 5197, 5212, 5226],
                [5240, 5267, 5293, 5317, 5340, 5361, 5382, 5402, 5421, 5439, 5456, 5473, 5489, 5505, 5520, 5534],
                [5549, 5576, 5601, 5625, 5648, 5670, 5690, 5710, 5729, 5747, 5764, 5781, 5797, 5813, 5828, 5843],
                [5857, 5884, 5909, 5933, 5956, 5978, 5998, 6018, 6037, 6055, 6073, 6090, 6106, 6121, 6136, 6151],
                [6165, 6192, 6217, 6242, 6264, 6286, 6307, 6326, 6345, 6364, 6381, 6398, 6414, 6430, 6445, 6459],
                [6473, 6500, 6526, 6550, 6573, 6594, 6615, 6635, 6654, 6672, 6689, 6706, 6722, 6738, 6753, 6767],
                [6782, 6809, 6834, 6858, 6881, 6903, 6923, 6943, 6962, 6980, 6998, 7014, 7030, 7046, 7061, 7076],
                [7090, 7117, 7142, 7166, 7189, 7211, 7231, 7251, 7270, 7288, 7306, 7323, 7339, 7354, 7369, 7384],
                [7398, 7425, 7450, 7475, 7497, 7519, 7540, 7560, 7578, 7597, 7614, 7631, 7647, 7663, 7678, 7692],
                [7706, 7733, 7759, 7783, 7806, 7827, 7848, 7868, 7887, 7905, 7922, 7939, 7955, 7971, 7986, 8001],
                [8015, 8042, 8067, 8091, 8114, 8136, 8156, 8176, 8195, 8213, 8231, 8247, 8263, 8279, 8294, 8309],
                [8323, 8350, 8375, 8399, 8422, 8444, 8464, 8484, 8503, 8521, 8539, 8556, 8572, 8587, 8602, 8617],
                [8631, 8658, 8684, 8708, 8730, 8752, 8773, 8793, 8811, 8830, 8847, 8864, 8880, 8896, 8911, 8925],
                [8939, 8966, 8992, 9016, 9039, 9060, 9081, 9101, 9120, 9138, 9155, 9172, 9188, 9204, 9219, 9234],
                [9248, 9275, 9300, 9324, 9347, 9369, 9389, 9409, 9428, 9446, 9464, 9480, 9497, 9512, 9527, 9542],
                [9556, 9583, 9608, 9632, 9655, 9677, 9698, 9717, 9736, 9754, 9772, 9789, 9805, 9820, 9835, 9850],
                [9864, 9891, 9917, 9941, 9963, 9985, 10006, 10026, 10044, 10063, 10080, 10097, 10113, 10129, 10144, 10158],
                [10172, 10199, 10225, 10249, 10272, 10293, 10314, 10334, 10353, 10371, 10388, 10405, 10421, 10437, 10452, 10467],
                [10481, 10508, 10533, 10557, 10580, 10602, 10622, 10642, 10661, 10679, 10697, 10713, 10730, 10745, 10760, 10775],
                [10789, 10816, 10841, 10865, 10888, 10910, 10931, 10950, 10969, 10987, 11005, 11022, 11038, 11053, 11068, 11083],
                [11097, 11124, 11150, 11174, 11196, 11218, 11239, 11259, 11277, 11296, 11313, 11330, 11346, 11362, 11377, 11391],
                [11405, 11432, 11458, 11482, 11505, 11526, 11547, 11567, 11586, 11604, 11621, 11638, 11654, 11670, 11685, 11700],
                [11714, 11741, 11766, 11790, 11813, 11835, 11855, 11875, 11894, 11912, 11930, 11946, 11963, 11978, 11993, 12008],
                [12022, 12049, 12074, 12098, 12121, 12143, 12164, 12183, 12202, 12220, 12238, 12255, 12271, 12286, 12301, 12316],
                [12330, 12357, 12383, 12407, 12429, 12451, 12472, 12492, 12511, 12529, 12546, 12563, 12579, 12595, 12610, 12624],
                [12638, 12665, 12691, 12715, 12738, 12759, 12780, 12800, 12819, 12837, 12854, 12871, 12887, 12903, 12918, 12933],
                [12947, 12974, 12999, 13023, 13046, 13068, 13088, 13108, 13127, 13145, 13163, 13179, 13196, 13211, 13226, 13241],
                [13255, 13282, 13307, 13331, 13354, 13376, 13397, 13416, 13435, 13453, 13471, 13488, 13504, 13519, 13535, 13549],
                [13563, 13590, 13616, 13640, 13662, 13684, 13705, 13725, 13744, 13762, 13779, 13796, 13812, 13828, 13843, 13857],
                [13871, 13898, 13924, 13948, 13971, 13992, 14013, 14033, 14052, 14070, 14087, 14104, 14120, 14136, 14151, 14166],
                [14180, 14207, 14232, 14256, 14279, 14301, 14321, 14341, 14360, 14378, 14396, 14412, 14429, 14444, 14459, 14474],
                [14488, 14515, 14540, 14564, 14587, 14609, 14630, 14649, 14668, 14686, 14704, 14721, 14737, 14752, 14768, 14782],
                [14796, 14823, 14849, 14873, 14895, 14917, 14938, 14958, 14977, 14995, 15012, 15029, 15045, 15061, 15076, 15090],
                [15104, 15131, 15157, 15181, 15204, 15225, 15246, 15266, 15285, 15303, 15320, 15337, 15353, 15369, 15384, 15399],
                [15413, 15440, 15465, 15489, 15512, 15534, 15554, 15574, 15593, 15611, 15629, 15645, 15662, 15677, 15692, 15707],
                [15721, 15748, 15773, 15797, 15820, 15842, 15863, 15882, 15901, 15919, 15937, 15954, 15970, 15985, 16001, 16015],
                [16029, 16056, 16082, 16106, 16128, 16150, 16171, 16191, 16210, 16228, 16245, 16262, 16278, 16294, 16309, 16323],
                [16337, 16364, 16390, 16414, 16437, 16458, 16479, 16499, 16518, 16536, 16553, 16570, 16586, 16602, 16617, 16632],
                [16646, 16673, 16698, 16722, 16745, 16767, 16787, 16807, 16826, 16844, 16862, 16878, 16895, 16910, 16925, 16940],
                [16954, 16981, 17006, 17030, 17053, 17075, 17096, 17115, 17134, 17152, 17170, 17187, 17203, 17218, 17234, 17248],
                [17262, 17289, 17315, 17339, 17361, 17383, 17404, 17424, 17443, 17461, 17478, 17495, 17511, 17527, 17542, 17556],
                [17571, 17597, 17623, 17647, 17670, 17691, 17712, 17732, 17751, 17769, 17786, 17803, 17819, 17835, 17850, 17865],
                [17879, 17906, 17931, 17955, 17978, 18000, 18020, 18040, 18059, 18077, 18095, 18111, 18128, 18143, 18158, 18173],
                [18187, 18214, 18239, 18263, 18286, 18308, 18329, 18348, 18367, 18385, 18403, 18420, 18436, 18452, 18467, 18481],
                [18495, 18522, 18548, 18572, 18595, 18616, 18637, 18657, 18676, 18694, 18711, 18728, 18744, 18760, 18775, 18789],
                [18804, 18830, 18856, 18880, 18903, 18924, 18945, 18965, 18984, 19002, 19019, 19036, 19052, 19068, 19083, 19098],
                [19112, 19139, 19164, 19188, 19211, 19233, 19253, 19273, 19292, 19310, 19328, 19344, 19361, 19376, 19391, 19406],
                [19420, 19447, 19472, 19496, 19519, 19541, 19562, 19581, 19600, 19619, 19636, 19653, 19669, 19685, 19700, 19714],
        ];

        /// Approximate `log10(numerator / denominator) * 1024` using a look-up table.
        #[inline]
        pub fn negative_log10_times_1024(numerator: u64, denominator: u64) -> u64 {
                // Multiply the -1 through to avoid needing to use signed numbers.
                (log10_times_1024(denominator) - log10_times_1024(numerator)) as u64
        }

        #[inline]
        fn log10_times_1024(x: u64) -> u16 {
                debug_assert_ne!(x, 0);
                let most_significant_bit = HIGHEST_BIT - x.leading_zeros();
                let lower_bits = (x >> most_significant_bit.saturating_sub(LOWER_BITS)) & LOWER_BITMASK;
                LOG10_TIMES_1024[most_significant_bit as usize][lower_bits as usize]
        }

        #[cfg(test)]
        mod tests {
                use super::*;

                #[test]
                fn prints_negative_log10_times_1024_lookup_table() {
                        for msb in 0..BITS {
                                for i in 0..LOWER_BITS_BOUND {
                                        let x = ((LOWER_BITS_BOUND + i) << (HIGHEST_BIT - LOWER_BITS)) >> (HIGHEST_BIT - msb);
                                        let log10_times_1024 = ((x as f64).log10() * 1024.0).round() as u16;
                                        assert_eq!(log10_times_1024, LOG10_TIMES_1024[msb as usize][i as usize]);

                                        if i % LOWER_BITS_BOUND == 0 {
                                                print!("\t\t[{}, ", log10_times_1024);
                                        } else if i % LOWER_BITS_BOUND == LOWER_BITS_BOUND - 1 {
                                                println!("{}],", log10_times_1024);
                                        } else {
                                                print!("{}, ", log10_times_1024);
                                        }
                                }
                        }
                }
        }
}

impl<G: Deref<Target = NetworkGraph>, T: Time> Writeable for ProbabilisticScorerUsingTime<G, T> {
        #[inline]
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
                write_tlv_fields!(w, {
                        (0, self.channel_liquidities, required)
                });
                Ok(())
        }
}

impl<G: Deref<Target = NetworkGraph>, T: Time>
ReadableArgs<(ProbabilisticScoringParameters, G)> for ProbabilisticScorerUsingTime<G, T> {
        #[inline]
        fn read<R: Read>(
                r: &mut R, args: (ProbabilisticScoringParameters, G)
        ) -> Result<Self, DecodeError> {
                let (params, network_graph) = args;
                let mut channel_liquidities = HashMap::new();
                read_tlv_fields!(r, {
                        (0, channel_liquidities, required)
                });
                Ok(Self {
                        params,
                        network_graph,
                        channel_liquidities,
                })
        }
}

impl<T: Time> Writeable for ChannelLiquidity<T> {
        #[inline]
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
                let duration_since_epoch = T::duration_since_epoch() - self.last_updated.elapsed();
                write_tlv_fields!(w, {
                        (0, self.min_liquidity_offset_msat, required),
                        (2, self.max_liquidity_offset_msat, required),
                        (4, duration_since_epoch, required),
                });
                Ok(())
        }
}

impl<T: Time> Readable for ChannelLiquidity<T> {
        #[inline]
        fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
                let mut min_liquidity_offset_msat = 0;
                let mut max_liquidity_offset_msat = 0;
                let mut duration_since_epoch = Duration::from_secs(0);
                read_tlv_fields!(r, {
                        (0, min_liquidity_offset_msat, required),
                        (2, max_liquidity_offset_msat, required),
                        (4, duration_since_epoch, required),
                });
                Ok(Self {
                        min_liquidity_offset_msat,
                        max_liquidity_offset_msat,
                        last_updated: T::now() - (T::duration_since_epoch() - duration_since_epoch),
                })
        }
}

pub(crate) mod time {
        use core::ops::Sub;
        use core::time::Duration;
        /// A measurement of time.
        pub trait Time: Copy + Sub<Duration, Output = Self> where Self: Sized {
                /// Returns an instance corresponding to the current moment.
                fn now() -> Self;

                /// Returns the amount of time elapsed since `self` was created.
                fn elapsed(&self) -> Duration;

                /// Returns the amount of time passed between `earlier` and `self`.
                fn duration_since(&self, earlier: Self) -> Duration;

                /// Returns the amount of time passed since the beginning of [`Time`].
                ///
                /// Used during (de-)serialization.
                fn duration_since_epoch() -> Duration;
        }

        /// A state in which time has no meaning.
        #[derive(Clone, Copy, Debug, PartialEq, Eq)]
        pub struct Eternity;

        #[cfg(not(feature = "no-std"))]
        impl Time for std::time::Instant {
                fn now() -> Self {
                        std::time::Instant::now()
                }

                fn duration_since(&self, earlier: Self) -> Duration {
                        self.duration_since(earlier)
                }

                fn duration_since_epoch() -> Duration {
                        use std::time::SystemTime;
                        SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap()
                }

                fn elapsed(&self) -> Duration {
                        std::time::Instant::elapsed(self)
                }
        }

        impl Time for Eternity {
                fn now() -> Self {
                        Self
                }

                fn duration_since(&self, _earlier: Self) -> Duration {
                        Duration::from_secs(0)
                }

                fn duration_since_epoch() -> Duration {
                        Duration::from_secs(0)
                }

                fn elapsed(&self) -> Duration {
                        Duration::from_secs(0)
                }
        }

        impl Sub<Duration> for Eternity {
                type Output = Self;

                fn sub(self, _other: Duration) -> Self {
                        self
                }
        }
}

pub(crate) use self::time::Time;

#[cfg(test)]
mod tests {
        use super::{ChannelLiquidity, ProbabilisticScoringParameters, ProbabilisticScorerUsingTime, ScoringParameters, ScorerUsingTime, Time};
        use super::time::Eternity;

        use ln::features::{ChannelFeatures, NodeFeatures};
        use ln::msgs::{ChannelAnnouncement, ChannelUpdate, OptionalField, UnsignedChannelAnnouncement, UnsignedChannelUpdate};
        use routing::scoring::Score;
        use routing::network_graph::{NetworkGraph, NodeId};
        use routing::router::RouteHop;
        use util::ser::{Readable, ReadableArgs, Writeable};

        use bitcoin::blockdata::constants::genesis_block;
        use bitcoin::hashes::Hash;
        use bitcoin::hashes::sha256d::Hash as Sha256dHash;
        use bitcoin::network::constants::Network;
        use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
        use core::cell::Cell;
        use core::ops::Sub;
        use core::time::Duration;
        use io;

        // `Time` tests

        /// Time that can be advanced manually in tests.
        #[derive(Clone, Copy, Debug, PartialEq, Eq)]
        struct SinceEpoch(Duration);

        impl SinceEpoch {
                thread_local! {
                        static ELAPSED: Cell<Duration> = core::cell::Cell::new(Duration::from_secs(0));
                }

                fn advance(duration: Duration) {
                        Self::ELAPSED.with(|elapsed| elapsed.set(elapsed.get() + duration))
                }
        }

        impl Time for SinceEpoch {
                fn now() -> Self {
                        Self(Self::duration_since_epoch())
                }

                fn duration_since(&self, earlier: Self) -> Duration {
                        self.0 - earlier.0
                }

                fn duration_since_epoch() -> Duration {
                        Self::ELAPSED.with(|elapsed| elapsed.get())
                }

                fn elapsed(&self) -> Duration {
                        Self::duration_since_epoch() - self.0
                }
        }

        impl Sub<Duration> for SinceEpoch {
                type Output = Self;

                fn sub(self, other: Duration) -> Self {
                        Self(self.0 - other)
                }
        }

        #[test]
        fn time_passes_when_advanced() {
                let now = SinceEpoch::now();
                assert_eq!(now.elapsed(), Duration::from_secs(0));

                SinceEpoch::advance(Duration::from_secs(1));
                SinceEpoch::advance(Duration::from_secs(1));

                let elapsed = now.elapsed();
                let later = SinceEpoch::now();

                assert_eq!(elapsed, Duration::from_secs(2));
                assert_eq!(later - elapsed, now);
        }

        #[test]
        fn time_never_passes_in_an_eternity() {
                let now = Eternity::now();
                let elapsed = now.elapsed();
                let later = Eternity::now();

                assert_eq!(now.elapsed(), Duration::from_secs(0));
                assert_eq!(later - elapsed, now);
        }

        // `Scorer` tests

        /// A scorer for testing with time that can be manually advanced.
        type Scorer = ScorerUsingTime::<SinceEpoch>;

        fn source_privkey() -> SecretKey {
                SecretKey::from_slice(&[42; 32]).unwrap()
        }

        fn target_privkey() -> SecretKey {
                SecretKey::from_slice(&[43; 32]).unwrap()
        }

        fn source_pubkey() -> PublicKey {
                let secp_ctx = Secp256k1::new();
                PublicKey::from_secret_key(&secp_ctx, &source_privkey())
        }

        fn target_pubkey() -> PublicKey {
                let secp_ctx = Secp256k1::new();
                PublicKey::from_secret_key(&secp_ctx, &target_privkey())
        }

        fn source_node_id() -> NodeId {
                NodeId::from_pubkey(&source_pubkey())
        }

        fn target_node_id() -> NodeId {
                NodeId::from_pubkey(&target_pubkey())
        }

        #[test]
        fn penalizes_without_channel_failures() {
                let scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(1),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                SinceEpoch::advance(Duration::from_secs(1));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
        }

        #[test]
        fn accumulates_channel_failure_penalties() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 64,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_064);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_128);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_192);
        }

        #[test]
        fn decays_channel_failure_penalties_over_time() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                SinceEpoch::advance(Duration::from_secs(9));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                SinceEpoch::advance(Duration::from_secs(1));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);

                SinceEpoch::advance(Duration::from_secs(10 * 8));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_001);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
        }

        #[test]
        fn decays_channel_failure_penalties_without_shift_overflow() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                // An unchecked right shift 64 bits or more in ChannelFailure::decayed_penalty_msat would
                // cause an overflow.
                SinceEpoch::advance(Duration::from_secs(10 * 64));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);
        }

        #[test]
        fn accumulates_channel_failure_penalties_after_decay() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_768);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_384);
        }

        #[test]
        fn reduces_channel_failure_penalties_after_success() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_000);

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);

                let hop = RouteHop {
                        pubkey: PublicKey::from_slice(target.as_slice()).unwrap(),
                        node_features: NodeFeatures::known(),
                        short_channel_id: 42,
                        channel_features: ChannelFeatures::known(),
                        fee_msat: 1,
                        cltv_expiry_delta: 18,
                };
                scorer.payment_path_successful(&[&hop]);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_128);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_064);
        }

        #[test]
        fn restores_persisted_channel_failure_penalties() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);

                scorer.payment_path_failed(&[], 43);
                assert_eq!(scorer.channel_penalty_msat(43, 1, 1, &source, &target), 1_512);

                let mut serialized_scorer = Vec::new();
                scorer.write(&mut serialized_scorer).unwrap();

                let deserialized_scorer = <Scorer>::read(&mut io::Cursor::new(&serialized_scorer)).unwrap();
                assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);
                assert_eq!(deserialized_scorer.channel_penalty_msat(43, 1, 1, &source, &target), 1_512);
        }

        #[test]
        fn decays_persisted_channel_failure_penalties() {
                let mut scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 1_000,
                        failure_penalty_msat: 512,
                        failure_penalty_half_life: Duration::from_secs(10),
                        overuse_penalty_start_1024th: 1024,
                        overuse_penalty_msat_per_1024th: 0,
                });
                let source = source_node_id();
                let target = target_node_id();

                scorer.payment_path_failed(&[], 42);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_512);

                let mut serialized_scorer = Vec::new();
                scorer.write(&mut serialized_scorer).unwrap();

                SinceEpoch::advance(Duration::from_secs(10));

                let deserialized_scorer = <Scorer>::read(&mut io::Cursor::new(&serialized_scorer)).unwrap();
                assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_256);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(deserialized_scorer.channel_penalty_msat(42, 1, 1, &source, &target), 1_128);
        }

        #[test]
        fn charges_per_1024th_penalty() {
                let scorer = Scorer::new(ScoringParameters {
                        base_penalty_msat: 0,
                        failure_penalty_msat: 0,
                        failure_penalty_half_life: Duration::from_secs(0),
                        overuse_penalty_start_1024th: 256,
                        overuse_penalty_msat_per_1024th: 100,
                });
                let source = source_node_id();
                let target = target_node_id();

                assert_eq!(scorer.channel_penalty_msat(42, 1_000, 1_024_000, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 256_999, 1_024_000, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 257_000, 1_024_000, &source, &target), 100);
                assert_eq!(scorer.channel_penalty_msat(42, 258_000, 1_024_000, &source, &target), 200);
                assert_eq!(scorer.channel_penalty_msat(42, 512_000, 1_024_000, &source, &target), 256 * 100);
        }

        // `ProbabilisticScorer` tests

        /// A probabilistic scorer for testing with time that can be manually advanced.
        type ProbabilisticScorer<'a> = ProbabilisticScorerUsingTime::<&'a NetworkGraph, SinceEpoch>;

        fn sender_privkey() -> SecretKey {
                SecretKey::from_slice(&[41; 32]).unwrap()
        }

        fn recipient_privkey() -> SecretKey {
                SecretKey::from_slice(&[45; 32]).unwrap()
        }

        fn sender_pubkey() -> PublicKey {
                let secp_ctx = Secp256k1::new();
                PublicKey::from_secret_key(&secp_ctx, &sender_privkey())
        }

        fn recipient_pubkey() -> PublicKey {
                let secp_ctx = Secp256k1::new();
                PublicKey::from_secret_key(&secp_ctx, &recipient_privkey())
        }

        fn sender_node_id() -> NodeId {
                NodeId::from_pubkey(&sender_pubkey())
        }

        fn recipient_node_id() -> NodeId {
                NodeId::from_pubkey(&recipient_pubkey())
        }

        fn network_graph() -> NetworkGraph {
                let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
                let mut network_graph = NetworkGraph::new(genesis_hash);
                add_channel(&mut network_graph, 42, source_privkey(), target_privkey());
                add_channel(&mut network_graph, 43, target_privkey(), recipient_privkey());

                network_graph
        }

        fn add_channel(
                network_graph: &mut NetworkGraph, short_channel_id: u64, node_1_key: SecretKey,
                node_2_key: SecretKey
        ) {
                let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
                let node_1_secret = &SecretKey::from_slice(&[39; 32]).unwrap();
                let node_2_secret = &SecretKey::from_slice(&[40; 32]).unwrap();
                let secp_ctx = Secp256k1::new();
                let unsigned_announcement = UnsignedChannelAnnouncement {
                        features: ChannelFeatures::known(),
                        chain_hash: genesis_hash,
                        short_channel_id,
                        node_id_1: PublicKey::from_secret_key(&secp_ctx, &node_1_key),
                        node_id_2: PublicKey::from_secret_key(&secp_ctx, &node_2_key),
                        bitcoin_key_1: PublicKey::from_secret_key(&secp_ctx, &node_1_secret),
                        bitcoin_key_2: PublicKey::from_secret_key(&secp_ctx, &node_2_secret),
                        excess_data: Vec::new(),
                };
                let msghash = hash_to_message!(&Sha256dHash::hash(&unsigned_announcement.encode()[..])[..]);
                let signed_announcement = ChannelAnnouncement {
                        node_signature_1: secp_ctx.sign(&msghash, &node_1_key),
                        node_signature_2: secp_ctx.sign(&msghash, &node_2_key),
                        bitcoin_signature_1: secp_ctx.sign(&msghash, &node_1_secret),
                        bitcoin_signature_2: secp_ctx.sign(&msghash, &node_2_secret),
                        contents: unsigned_announcement,
                };
                let chain_source: Option<&::util::test_utils::TestChainSource> = None;
                network_graph.update_channel_from_announcement(
                        &signed_announcement, &chain_source, &secp_ctx).unwrap();
                update_channel(network_graph, short_channel_id, node_1_key, 0);
                update_channel(network_graph, short_channel_id, node_2_key, 1);
        }

        fn update_channel(
                network_graph: &mut NetworkGraph, short_channel_id: u64, node_key: SecretKey, flags: u8
        ) {
                let genesis_hash = genesis_block(Network::Testnet).header.block_hash();
                let secp_ctx = Secp256k1::new();
                let unsigned_update = UnsignedChannelUpdate {
                        chain_hash: genesis_hash,
                        short_channel_id,
                        timestamp: 100,
                        flags,
                        cltv_expiry_delta: 18,
                        htlc_minimum_msat: 0,
                        htlc_maximum_msat: OptionalField::Present(1_000),
                        fee_base_msat: 1,
                        fee_proportional_millionths: 0,
                        excess_data: Vec::new(),
                };
                let msghash = hash_to_message!(&Sha256dHash::hash(&unsigned_update.encode()[..])[..]);
                let signed_update = ChannelUpdate {
                        signature: secp_ctx.sign(&msghash, &node_key),
                        contents: unsigned_update,
                };
                network_graph.update_channel(&signed_update, &secp_ctx).unwrap();
        }

        fn payment_path_for_amount(amount_msat: u64) -> Vec<RouteHop> {
                vec![
                        RouteHop {
                                pubkey: source_pubkey(),
                                node_features: NodeFeatures::known(),
                                short_channel_id: 41,
                                channel_features: ChannelFeatures::known(),
                                fee_msat: 1,
                                cltv_expiry_delta: 18,
                        },
                        RouteHop {
                                pubkey: target_pubkey(),
                                node_features: NodeFeatures::known(),
                                short_channel_id: 42,
                                channel_features: ChannelFeatures::known(),
                                fee_msat: 2,
                                cltv_expiry_delta: 18,
                        },
                        RouteHop {
                                pubkey: recipient_pubkey(),
                                node_features: NodeFeatures::known(),
                                short_channel_id: 43,
                                channel_features: ChannelFeatures::known(),
                                fee_msat: amount_msat,
                                cltv_expiry_delta: 18,
                        },
                ]
        }

        #[test]
        fn liquidity_bounds_directed_from_lowest_node_id() {
                let last_updated = SinceEpoch::now();
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters::default();
                let mut scorer = ProbabilisticScorer::new(params, &network_graph)
                        .with_channel(42,
                                ChannelLiquidity {
                                        min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100, last_updated
                                })
                        .with_channel(43,
                                ChannelLiquidity {
                                        min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100, last_updated
                                });
                let source = source_node_id();
                let target = target_node_id();
                let recipient = recipient_node_id();
                assert!(source > target);
                assert!(target < recipient);

                // Update minimum liquidity.

                let liquidity_offset_half_life = scorer.params.liquidity_offset_half_life;
                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 100);
                assert_eq!(liquidity.max_liquidity_msat(), 300);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 700);
                assert_eq!(liquidity.max_liquidity_msat(), 900);

                scorer.channel_liquidities.get_mut(&42).unwrap()
                        .as_directed_mut(&source, &target, 1_000, liquidity_offset_half_life)
                        .set_min_liquidity_msat(200);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 200);
                assert_eq!(liquidity.max_liquidity_msat(), 300);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 700);
                assert_eq!(liquidity.max_liquidity_msat(), 800);

                // Update maximum liquidity.

                let liquidity = scorer.channel_liquidities.get(&43).unwrap()
                        .as_directed(&target, &recipient, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 700);
                assert_eq!(liquidity.max_liquidity_msat(), 900);

                let liquidity = scorer.channel_liquidities.get(&43).unwrap()
                        .as_directed(&recipient, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 100);
                assert_eq!(liquidity.max_liquidity_msat(), 300);

                scorer.channel_liquidities.get_mut(&43).unwrap()
                        .as_directed_mut(&target, &recipient, 1_000, liquidity_offset_half_life)
                        .set_max_liquidity_msat(200);

                let liquidity = scorer.channel_liquidities.get(&43).unwrap()
                        .as_directed(&target, &recipient, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 0);
                assert_eq!(liquidity.max_liquidity_msat(), 200);

                let liquidity = scorer.channel_liquidities.get(&43).unwrap()
                        .as_directed(&recipient, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 800);
                assert_eq!(liquidity.max_liquidity_msat(), 1000);
        }

        #[test]
        fn resets_liquidity_upper_bound_when_crossed_by_lower_bound() {
                let last_updated = SinceEpoch::now();
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters::default();
                let mut scorer = ProbabilisticScorer::new(params, &network_graph)
                        .with_channel(42,
                                ChannelLiquidity {
                                        min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400, last_updated
                                });
                let source = source_node_id();
                let target = target_node_id();
                assert!(source > target);

                // Check initial bounds.
                let liquidity_offset_half_life = scorer.params.liquidity_offset_half_life;
                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 400);
                assert_eq!(liquidity.max_liquidity_msat(), 800);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 200);
                assert_eq!(liquidity.max_liquidity_msat(), 600);

                // Reset from source to target.
                scorer.channel_liquidities.get_mut(&42).unwrap()
                        .as_directed_mut(&source, &target, 1_000, liquidity_offset_half_life)
                        .set_min_liquidity_msat(900);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 900);
                assert_eq!(liquidity.max_liquidity_msat(), 1_000);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 0);
                assert_eq!(liquidity.max_liquidity_msat(), 100);

                // Reset from target to source.
                scorer.channel_liquidities.get_mut(&42).unwrap()
                        .as_directed_mut(&target, &source, 1_000, liquidity_offset_half_life)
                        .set_min_liquidity_msat(400);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 0);
                assert_eq!(liquidity.max_liquidity_msat(), 600);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 400);
                assert_eq!(liquidity.max_liquidity_msat(), 1_000);
        }

        #[test]
        fn resets_liquidity_lower_bound_when_crossed_by_upper_bound() {
                let last_updated = SinceEpoch::now();
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters::default();
                let mut scorer = ProbabilisticScorer::new(params, &network_graph)
                        .with_channel(42,
                                ChannelLiquidity {
                                        min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400, last_updated
                                });
                let source = source_node_id();
                let target = target_node_id();
                assert!(source > target);

                // Check initial bounds.
                let liquidity_offset_half_life = scorer.params.liquidity_offset_half_life;
                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 400);
                assert_eq!(liquidity.max_liquidity_msat(), 800);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 200);
                assert_eq!(liquidity.max_liquidity_msat(), 600);

                // Reset from source to target.
                scorer.channel_liquidities.get_mut(&42).unwrap()
                        .as_directed_mut(&source, &target, 1_000, liquidity_offset_half_life)
                        .set_max_liquidity_msat(300);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 0);
                assert_eq!(liquidity.max_liquidity_msat(), 300);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 700);
                assert_eq!(liquidity.max_liquidity_msat(), 1_000);

                // Reset from target to source.
                scorer.channel_liquidities.get_mut(&42).unwrap()
                        .as_directed_mut(&target, &source, 1_000, liquidity_offset_half_life)
                        .set_max_liquidity_msat(600);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&source, &target, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 400);
                assert_eq!(liquidity.max_liquidity_msat(), 1_000);

                let liquidity = scorer.channel_liquidities.get(&42).unwrap()
                        .as_directed(&target, &source, 1_000, liquidity_offset_half_life);
                assert_eq!(liquidity.min_liquidity_msat(), 0);
                assert_eq!(liquidity.max_liquidity_msat(), 600);
        }

        #[test]
        fn increased_penalty_nearing_liquidity_upper_bound() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();

                assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024_000, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 10_240, 1_024_000, &source, &target), 14);
                assert_eq!(scorer.channel_penalty_msat(42, 102_400, 1_024_000, &source, &target), 43);
                assert_eq!(scorer.channel_penalty_msat(42, 1_024_000, 1_024_000, &source, &target), 2_000);

                assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 58);
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 125);
                assert_eq!(scorer.channel_penalty_msat(42, 374, 1_024, &source, &target), 204);
                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 301);
                assert_eq!(scorer.channel_penalty_msat(42, 640, 1_024, &source, &target), 426);
                assert_eq!(scorer.channel_penalty_msat(42, 768, 1_024, &source, &target), 602);
                assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), 903);
        }

        #[test]
        fn constant_penalty_outside_liquidity_bounds() {
                let last_updated = SinceEpoch::now();
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph)
                        .with_channel(42,
                                ChannelLiquidity {
                                        min_liquidity_offset_msat: 40, max_liquidity_offset_msat: 40, last_updated
                                });
                let source = source_node_id();
                let target = target_node_id();

                assert_eq!(scorer.channel_penalty_msat(42, 39, 100, &source, &target), 0);
                assert_ne!(scorer.channel_penalty_msat(42, 50, 100, &source, &target), 0);
                assert_ne!(scorer.channel_penalty_msat(42, 50, 100, &source, &target), u64::max_value());
                assert_eq!(scorer.channel_penalty_msat(42, 61, 100, &source, &target), u64::max_value());
        }

        #[test]
        fn does_not_further_penalize_own_channel() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let sender = sender_node_id();
                let source = source_node_id();
                let failed_path = payment_path_for_amount(500);
                let successful_path = payment_path_for_amount(200);

                assert_eq!(scorer.channel_penalty_msat(41, 500, 1_000, &sender, &source), 300);

                scorer.payment_path_failed(&failed_path.iter().collect::<Vec<_>>(), 41);
                assert_eq!(scorer.channel_penalty_msat(41, 500, 1_000, &sender, &source), 300);

                scorer.payment_path_successful(&successful_path.iter().collect::<Vec<_>>());
                assert_eq!(scorer.channel_penalty_msat(41, 500, 1_000, &sender, &source), 300);
        }

        #[test]
        fn sets_liquidity_lower_bound_on_downstream_failure() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();
                let path = payment_path_for_amount(500);

                assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 128);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
                assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 601);

                scorer.payment_path_failed(&path.iter().collect::<Vec<_>>(), 43);

                assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 300);
        }

        #[test]
        fn sets_liquidity_upper_bound_on_failure() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();
                let path = payment_path_for_amount(500);

                assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 128);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
                assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), 601);

                scorer.payment_path_failed(&path.iter().collect::<Vec<_>>(), 42);

                assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 300);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), u64::max_value());
                assert_eq!(scorer.channel_penalty_msat(42, 750, 1_000, &source, &target), u64::max_value());
        }

        #[test]
        fn reduces_liquidity_upper_bound_along_path_on_success() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let sender = sender_node_id();
                let source = source_node_id();
                let target = target_node_id();
                let recipient = recipient_node_id();
                let path = payment_path_for_amount(500);

                assert_eq!(scorer.channel_penalty_msat(41, 250, 1_000, &sender, &source), 128);
                assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 128);
                assert_eq!(scorer.channel_penalty_msat(43, 250, 1_000, &target, &recipient), 128);

                scorer.payment_path_successful(&path.iter().collect::<Vec<_>>());

                assert_eq!(scorer.channel_penalty_msat(41, 250, 1_000, &sender, &source), 128);
                assert_eq!(scorer.channel_penalty_msat(42, 250, 1_000, &source, &target), 300);
                assert_eq!(scorer.channel_penalty_msat(43, 250, 1_000, &target, &recipient), 300);
        }

        #[test]
        fn decays_liquidity_bounds_over_time() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        liquidity_offset_half_life: Duration::from_secs(10),
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();

                assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);

                scorer.payment_path_failed(&payment_path_for_amount(768).iter().collect::<Vec<_>>(), 42);
                scorer.payment_path_failed(&payment_path_for_amount(128).iter().collect::<Vec<_>>(), 43);

                assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 97);
                assert_eq!(scorer.channel_penalty_msat(42, 768, 1_024, &source, &target), 1_409);
                assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), u64::max_value());

                SinceEpoch::advance(Duration::from_secs(9));
                assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 97);
                assert_eq!(scorer.channel_penalty_msat(42, 768, 1_024, &source, &target), 1_409);
                assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), u64::max_value());

                SinceEpoch::advance(Duration::from_secs(1));
                assert_eq!(scorer.channel_penalty_msat(42, 64, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 34);
                assert_eq!(scorer.channel_penalty_msat(42, 896, 1_024, &source, &target), 1_773);
                assert_eq!(scorer.channel_penalty_msat(42, 960, 1_024, &source, &target), u64::max_value());

                // Fully decay liquidity lower bound.
                SinceEpoch::advance(Duration::from_secs(10 * 7));
                assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 1, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 1_023, 1_024, &source, &target), 2_000);
                assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);

                // Fully decay liquidity upper bound.
                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 0, 1_024, &source, &target), 0);
                assert_eq!(scorer.channel_penalty_msat(42, 1_024, 1_024, &source, &target), 2_000);
        }

        #[test]
        fn decays_liquidity_bounds_without_shift_overflow() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        liquidity_offset_half_life: Duration::from_secs(10),
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 125);

                scorer.payment_path_failed(&payment_path_for_amount(512).iter().collect::<Vec<_>>(), 42);
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 274);

                // An unchecked right shift 64 bits or more in DirectedChannelLiquidity::decayed_offset_msat
                // would cause an overflow.
                SinceEpoch::advance(Duration::from_secs(10 * 64));
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 125);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 256, 1_024, &source, &target), 125);
        }

        #[test]
        fn restricts_liquidity_bounds_after_decay() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        liquidity_offset_half_life: Duration::from_secs(10),
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();

                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 301);

                // More knowledge gives higher confidence (256, 768), meaning a lower penalty.
                scorer.payment_path_failed(&payment_path_for_amount(768).iter().collect::<Vec<_>>(), 42);
                scorer.payment_path_failed(&payment_path_for_amount(256).iter().collect::<Vec<_>>(), 43);
                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 274);

                // Decaying knowledge gives less confidence (128, 896), meaning a higher penalty.
                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 301);

                // Reducing the upper bound gives more confidence (128, 832) that the payment amount (512)
                // is closer to the upper bound, meaning a higher penalty.
                scorer.payment_path_successful(&payment_path_for_amount(64).iter().collect::<Vec<_>>());
                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 342);

                // Increasing the lower bound gives more confidence (256, 832) that the payment amount (512)
                // is closer to the lower bound, meaning a lower penalty.
                scorer.payment_path_failed(&payment_path_for_amount(256).iter().collect::<Vec<_>>(), 43);
                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 255);

                // Further decaying affects the lower bound more than the upper bound (128, 928).
                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 512, 1_024, &source, &target), 284);
        }

        #[test]
        fn restores_persisted_liquidity_bounds() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        liquidity_offset_half_life: Duration::from_secs(10),
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();

                scorer.payment_path_failed(&payment_path_for_amount(500).iter().collect::<Vec<_>>(), 42);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), u64::max_value());

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 472);

                scorer.payment_path_failed(&payment_path_for_amount(250).iter().collect::<Vec<_>>(), 43);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);

                let mut serialized_scorer = Vec::new();
                scorer.write(&mut serialized_scorer).unwrap();

                let mut serialized_scorer = io::Cursor::new(&serialized_scorer);
                let deserialized_scorer =
                        <ProbabilisticScorer>::read(&mut serialized_scorer, (params, &network_graph)).unwrap();
                assert_eq!(deserialized_scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);
        }

        #[test]
        fn decays_persisted_liquidity_bounds() {
                let network_graph = network_graph();
                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        liquidity_offset_half_life: Duration::from_secs(10),
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let mut scorer = ProbabilisticScorer::new(params, &network_graph);
                let source = source_node_id();
                let target = target_node_id();

                scorer.payment_path_failed(&payment_path_for_amount(500).iter().collect::<Vec<_>>(), 42);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), u64::max_value());

                let mut serialized_scorer = Vec::new();
                scorer.write(&mut serialized_scorer).unwrap();

                SinceEpoch::advance(Duration::from_secs(10));

                let mut serialized_scorer = io::Cursor::new(&serialized_scorer);
                let deserialized_scorer =
                        <ProbabilisticScorer>::read(&mut serialized_scorer, (params, &network_graph)).unwrap();
                assert_eq!(deserialized_scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 472);

                scorer.payment_path_failed(&payment_path_for_amount(250).iter().collect::<Vec<_>>(), 43);
                assert_eq!(scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 300);

                SinceEpoch::advance(Duration::from_secs(10));
                assert_eq!(deserialized_scorer.channel_penalty_msat(42, 500, 1_000, &source, &target), 371);
        }

        #[test]
        fn adds_base_penalty_to_liquidity_penalty() {
                let network_graph = network_graph();
                let source = source_node_id();
                let target = target_node_id();

                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph);
                assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 58);

                let params = ProbabilisticScoringParameters {
                        base_penalty_msat: 500, liquidity_penalty_multiplier_msat: 1_000, ..Default::default()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph);
                assert_eq!(scorer.channel_penalty_msat(42, 128, 1_024, &source, &target), 558);
        }

        #[test]
        fn adds_amount_penalty_to_liquidity_penalty() {
                let network_graph = network_graph();
                let source = source_node_id();
                let target = target_node_id();

                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        amount_penalty_multiplier_msat: 0,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph);
                assert_eq!(scorer.channel_penalty_msat(42, 512_000, 1_024_000, &source, &target), 300);

                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 1_000,
                        amount_penalty_multiplier_msat: 256,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph);
                assert_eq!(scorer.channel_penalty_msat(42, 512_000, 1_024_000, &source, &target), 337);
        }

        #[test]
        fn calculates_log10_without_overflowing_u64_max_value() {
                let network_graph = network_graph();
                let source = source_node_id();
                let target = target_node_id();

                let params = ProbabilisticScoringParameters {
                        liquidity_penalty_multiplier_msat: 40_000,
                        ..ProbabilisticScoringParameters::zero_penalty()
                };
                let scorer = ProbabilisticScorer::new(params, &network_graph);
                assert_eq!(
                        scorer.channel_penalty_msat(42, u64::max_value(), u64::max_value(), &source, &target),
                        80_000,
                );
        }
}