[rust-lightning] / lightning / src / util / indexed_map.rs

//! This module has a map which can be iterated in a deterministic order. See the [`IndexedMap`].

use crate::prelude::*;
use alloc::slice::Iter;
use core::hash::Hash;
use core::ops::{Bound, RangeBounds};

/// A map which can be iterated in a deterministic order.
///
/// This would traditionally be accomplished by simply using a [`BTreeMap`], however B-Trees
/// generally have very slow lookups. Because we use a nodes+channels map while finding routes
/// across the network graph, our network graph backing map must be as performant as possible.
/// However, because peers expect to sync the network graph from us (and we need to support that
/// without holding a lock on the graph for the duration of the sync or dumping the entire graph
/// into our outbound message queue), we need an iterable map with a consistent iteration order we
/// can jump to a starting point on.
///
/// Thus, we have a custom data structure here - its API mimics that of Rust's [`BTreeMap`], but is
/// actually backed by a [`HashMap`], with some additional tracking to ensure we can iterate over
/// keys in the order defined by [`Ord`].
///
/// This is not exported to bindings users as bindings provide alternate accessors rather than exposing maps directly.
///
/// [`BTreeMap`]: alloc::collections::BTreeMap
#[derive(Clone, Debug, Eq)]
pub struct IndexedMap<K: Hash + Ord, V> {
        map: HashMap<K, V>,
        keys: Vec<K>,
}

impl<K: Clone + Hash + Ord, V> IndexedMap<K, V> {
        /// Constructs a new, empty map
        pub fn new() -> Self {
                Self {
                        map: new_hash_map(),
                        keys: Vec::new(),
                }
        }

        /// Constructs a new, empty map with the given capacity pre-allocated
        pub fn with_capacity(capacity: usize) -> Self {
                Self {
                        map: hash_map_with_capacity(capacity),
                        keys: Vec::with_capacity(capacity),
                }
        }

        #[inline(always)]
        /// Fetches the element with the given `key`, if one exists.
        pub fn get(&self, key: &K) -> Option<&V> {
                self.map.get(key)
        }

        /// Fetches a mutable reference to the element with the given `key`, if one exists.
        pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
                self.map.get_mut(key)
        }

        #[inline]
        /// Returns true if an element with the given `key` exists in the map.
        pub fn contains_key(&self, key: &K) -> bool {
                self.map.contains_key(key)
        }

        /// Removes the element with the given `key`, returning it, if one exists.
        pub fn remove(&mut self, key: &K) -> Option<V> {
                let ret = self.map.remove(key);
                if let Some(_) = ret {
                        let idx = self.keys.iter().position(|k| k == key).expect("map and keys must be consistent");
                        self.keys.remove(idx);
                }
                ret
        }

        /// Inserts the given `key`/`value` pair into the map, returning the element that was
        /// previously stored at the given `key`, if one exists.
        pub fn insert(&mut self, key: K, value: V) -> Option<V> {
                let ret = self.map.insert(key.clone(), value);
                if ret.is_none() {
                        self.keys.push(key);
                }
                ret
        }

        /// Returns an [`Entry`] for the given `key` in the map, allowing access to the value.
        pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
                match self.map.entry(key.clone()) {
                        hash_map::Entry::Vacant(entry) => {
                                Entry::Vacant(VacantEntry {
                                        underlying_entry: entry,
                                        key,
                                        keys: &mut self.keys,
                                })
                        },
                        hash_map::Entry::Occupied(entry) => {
                                Entry::Occupied(OccupiedEntry {
                                        underlying_entry: entry,
                                        keys: &mut self.keys,
                                })
                        }
                }
        }

        /// Returns an iterator which iterates over the keys in the map, in a random order.
        pub fn unordered_keys(&self) -> impl Iterator<Item = &K> {
                self.map.keys()
        }

        /// Returns an iterator which iterates over the `key`/`value` pairs in a random order.
        pub fn unordered_iter(&self) -> impl Iterator<Item = (&K, &V)> {
                self.map.iter()
        }

        /// Returns an iterator which iterates over the `key`s and mutable references to `value`s in a
        /// random order.
        pub fn unordered_iter_mut(&mut self) -> impl Iterator<Item = (&K, &mut V)> {
                self.map.iter_mut()
        }

        /// Returns an iterator which iterates over the `key`/`value` pairs in a given range.
        pub fn range<R: RangeBounds<K>>(&mut self, range: R) -> Range<K, V> {
                self.keys.sort_unstable();
                let start = match range.start_bound() {
                        Bound::Unbounded => 0,
                        Bound::Included(key) => self.keys.binary_search(key).unwrap_or_else(|index| index),
                        Bound::Excluded(key) => self.keys.binary_search(key).and_then(|index| Ok(index + 1)).unwrap_or_else(|index| index),
                };
                let end = match range.end_bound() {
                        Bound::Unbounded => self.keys.len(),
                        Bound::Included(key) => self.keys.binary_search(key).and_then(|index| Ok(index + 1)).unwrap_or_else(|index| index),
                        Bound::Excluded(key) => self.keys.binary_search(key).unwrap_or_else(|index| index),
                };

                Range {
                        inner_range: self.keys[start..end].iter(),
                        map: &self.map,
                }
        }

        /// Returns the number of `key`/`value` pairs in the map
        pub fn len(&self) -> usize {
                self.map.len()
        }

        /// Returns true if there are no elements in the map
        pub fn is_empty(&self) -> bool {
                self.map.is_empty()
        }
}

impl<K: Hash + Ord + PartialEq, V: PartialEq> PartialEq for IndexedMap<K, V> {
        fn eq(&self, other: &Self) -> bool {
                self.map == other.map
        }
}

/// An iterator over a range of values in an [`IndexedMap`]
///
/// This is not exported to bindings users as bindings provide alternate accessors rather than exposing maps directly.
pub struct Range<'a, K: Hash + Ord, V> {
        inner_range: Iter<'a, K>,
        map: &'a HashMap<K, V>,
}
impl<'a, K: Hash + Ord, V: 'a> Iterator for Range<'a, K, V> {
        type Item = (&'a K, &'a V);
        fn next(&mut self) -> Option<(&'a K, &'a V)> {
                self.inner_range.next().map(|k| {
                        (k, self.map.get(k).expect("map and keys must be consistent"))
                })
        }
}

/// An [`Entry`] for a key which currently has no value
///
/// This is not exported to bindings users as bindings provide alternate accessors rather than exposing maps directly.
pub struct VacantEntry<'a, K: Hash + Ord, V> {
        underlying_entry: VacantHashMapEntry<'a, K, V>,
        key: K,
        keys: &'a mut Vec<K>,
}

/// An [`Entry`] for an existing key-value pair
///
/// This is not exported to bindings users as bindings provide alternate accessors rather than exposing maps directly.
pub struct OccupiedEntry<'a, K: Hash + Ord, V> {
        underlying_entry: OccupiedHashMapEntry<'a, K, V>,
        keys: &'a mut Vec<K>,
}

/// A mutable reference to a position in the map. This can be used to reference, add, or update the
/// value at a fixed key.
///
/// This is not exported to bindings users as bindings provide alternate accessors rather than exposing maps directly.
pub enum Entry<'a, K: Hash + Ord, V> {
        /// A mutable reference to a position within the map where there is no value.
        Vacant(VacantEntry<'a, K, V>),
        /// A mutable reference to a position within the map where there is currently a value.
        Occupied(OccupiedEntry<'a, K, V>),
}

impl<'a, K: Hash + Ord, V> VacantEntry<'a, K, V> {
        /// Insert a value into the position described by this entry.
        pub fn insert(self, value: V) -> &'a mut V {
                self.keys.push(self.key);
                self.underlying_entry.insert(value)
        }
}

impl<'a, K: Hash + Ord, V> OccupiedEntry<'a, K, V> {
        /// Remove the value at the position described by this entry.
        pub fn remove_entry(self) -> (K, V) {
                let res = self.underlying_entry.remove_entry();
                let idx = self.keys.iter().position(|k| k == &res.0).expect("map and keys must be consistent");
                self.keys.remove(idx);
                res
        }

        /// Get a reference to the value at the position described by this entry.
        pub fn get(&self) -> &V {
                self.underlying_entry.get()
        }

        /// Get a mutable reference to the value at the position described by this entry.
        pub fn get_mut(&mut self) -> &mut V {
                self.underlying_entry.get_mut()
        }

        /// Consume this entry, returning a mutable reference to the value at the position described by
        /// this entry.
        pub fn into_mut(self) -> &'a mut V {
                self.underlying_entry.into_mut()
        }
}