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//! Implements a map type that preserves insertion order.
use crate::{object::JsObject, JsData, JsValue};
use boa_gc::{custom_trace, Finalize, Trace};
use indexmap::{Equivalent, IndexMap};
use std::{
fmt::Debug,
hash::{Hash, Hasher},
};
#[derive(PartialEq, Eq, Clone, Debug)]
pub(crate) enum MapKey {
Key(JsValue),
Empty(usize), // Necessary to ensure empty keys are still unique.
}
// This ensures that a MapKey::Key(value) hashes to the same as value. The derived PartialEq implementation still holds.
impl Hash for MapKey {
fn hash<H: Hasher>(&self, state: &mut H) {
match self {
Self::Key(v) => v.hash(state),
Self::Empty(e) => e.hash(state),
}
}
}
impl Equivalent<MapKey> for JsValue {
fn equivalent(&self, key: &MapKey) -> bool {
match key {
MapKey::Key(v) => v == self,
MapKey::Empty(_) => false,
}
}
}
/// A structure wrapping `indexmap::IndexMap`.
#[derive(Clone, Finalize, JsData)]
pub struct OrderedMap<V> {
map: IndexMap<MapKey, Option<V>>,
lock: u32,
empty_count: usize,
}
unsafe impl<V: Trace> Trace for OrderedMap<V> {
custom_trace!(this, mark, {
for (k, v) in &this.map {
if let MapKey::Key(key) = k {
mark(key);
}
mark(v);
}
});
}
impl<V: Debug> Debug for OrderedMap<V> {
fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
self.map.fmt(formatter)
}
}
impl<V> Default for OrderedMap<V> {
fn default() -> Self {
Self::new()
}
}
impl<V> OrderedMap<V> {
/// Creates a new empty `OrderedMap`.
#[must_use]
pub fn new() -> Self {
Self {
map: IndexMap::new(),
lock: 0,
empty_count: 0,
}
}
/// Creates a new empty `OrderedMap` with the specified capacity.
#[must_use]
pub fn with_capacity(capacity: usize) -> Self {
Self {
map: IndexMap::with_capacity(capacity),
lock: 0,
empty_count: 0,
}
}
/// Return the number of key-value pairs in the map, including empty values.
///
/// Computes in **O(1)** time.
#[must_use]
pub fn full_len(&self) -> usize {
self.map.len()
}
/// Gets the number of key-value pairs in the map, not including empty values.
///
/// Computes in **O(1)** time.
#[must_use]
pub fn len(&self) -> usize {
self.map.len() - self.empty_count
}
/// Returns true if the map contains no elements.
///
/// Computes in **O(1)** time.
#[must_use]
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Insert a key-value pair in the map.
///
/// If an equivalent key already exists in the map: the key remains and
/// retains in its place in the order, its corresponding value is updated
/// with `value` and the older value is returned inside `Some(_)`.
///
/// If no equivalent key existed in the map: the new key-value pair is
/// inserted, last in order, and `None` is returned.
///
/// Computes in **O(1)** time (amortized average).
pub fn insert(&mut self, key: JsValue, value: V) -> Option<V> {
self.map.insert(MapKey::Key(key), Some(value)).flatten()
}
/// Remove the key-value pair equivalent to `key` and return
/// its value.
///
/// Like `Vec::remove`, the pair is removed by shifting all of the
/// elements that follow it, preserving their relative order.
/// **This perturbs the index of all of those elements!**
///
/// Return `None` if `key` is not in map.
///
/// Computes in **O(n)** time (average).
pub fn remove(&mut self, key: &JsValue) -> Option<V> {
if self.lock == 0 {
self.map.shift_remove(key).flatten()
} else if self.map.contains_key(key) {
self.map.insert(MapKey::Empty(self.empty_count), None);
self.empty_count += 1;
self.map.swap_remove(key).flatten()
} else {
None
}
}
/// Removes all elements from the map and resets the counter of
/// empty entries.
pub fn clear(&mut self) {
self.map.clear();
self.map.shrink_to_fit();
self.empty_count = 0;
}
/// Return a reference to the value stored for `key`, if it is present,
/// else `None`.
///
/// Computes in **O(1)** time (average).
pub fn get(&self, key: &JsValue) -> Option<&V> {
self.map.get(key).and_then(Option::as_ref)
}
/// Get a key-value pair by index.
///
/// Valid indices are `0 <= index < self.full_len()`.
///
/// Computes in O(1) time.
#[must_use]
pub fn get_index(&self, index: usize) -> Option<(&JsValue, &V)> {
if let (MapKey::Key(key), Some(value)) = self.map.get_index(index)? {
Some((key, value))
} else {
None
}
}
/// Return an iterator over the key-value pairs of the map, in their order
pub fn iter(&self) -> impl Iterator<Item = (&JsValue, &V)> {
self.map.iter().filter_map(|o| {
if let (MapKey::Key(key), Some(value)) = o {
Some((key, value))
} else {
None
}
})
}
/// Return `true` if an equivalent to `key` exists in the map.
///
/// Computes in **O(1)** time (average).
#[must_use]
pub fn contains_key(&self, key: &JsValue) -> bool {
self.map.contains_key(key)
}
/// Increases the lock counter and returns a lock object that will decrement the counter when dropped.
///
/// This allows objects to be removed from the map during iteration without affecting the indexes until the iteration has completed.
pub(crate) fn lock(&mut self, map: JsObject) -> MapLock {
self.lock += 1;
MapLock(map)
}
/// Decreases the lock counter and, if 0, removes all empty entries.
fn unlock(&mut self) {
self.lock -= 1;
if self.lock == 0 {
self.map.retain(|k, _| matches!(k, MapKey::Key(_)));
self.empty_count = 0;
}
}
}
/// Increases the lock count of the map for the lifetime of the guard. This should not be dropped until iteration has completed.
#[derive(Debug, Trace)]
pub(crate) struct MapLock(JsObject);
impl Finalize for MapLock {
fn finalize(&self) {
// Avoids panicking inside `Finalize`, with the downside of slightly increasing
// memory usage if the map could not be borrowed.
let Ok(mut map) = self.0.try_borrow_mut() else {
return;
};
map.downcast_mut::<OrderedMap<JsValue>>()
.expect("MapLock does not point to a map")
.unlock();
}
}