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use itertools::Itertools;
use std::collections::HashMap;
use std::hash::Hash;
use std::ops::Index;
#[derive(Debug, Clone)]
pub(crate) struct IndexedCache<T> {
pub(crate) cache: Vec<T>,
lookup: HashMap<T, usize>,
}
impl<T> PartialEq for IndexedCache<T>
where
T: PartialEq,
{
fn eq(&self, other: &Self) -> bool {
self.cache == other.cache
}
}
impl<T> IndexedCache<T>
where
T: Clone + Eq + Hash + Ord,
{
pub(crate) fn new() -> Self {
IndexedCache {
cache: Default::default(),
lookup: Default::default(),
}
}
pub(crate) fn cache(&mut self, item: T) -> usize {
if let Some(n) = self.lookup.get(&item) {
*n
} else {
let n = self.cache.len();
self.cache.push(item.clone());
self.lookup.insert(item, n);
n
}
}
pub(crate) fn lookup(&self, item: &T) -> Option<usize> {
self.lookup.get(item).cloned()
}
#[allow(dead_code)]
pub(crate) fn len(&self) -> usize {
self.cache.len()
}
pub(crate) fn get(&self, index: usize) -> &T {
&self.cache[index]
}
pub(crate) fn safe_get(&self, index: usize) -> Option<&T> {
self.cache.get(index)
}
/// Remove the last inserted entry into this cache.
/// This is safe to do as it does not require reshuffling other entries.
///
/// # Panics
///
/// Panics on an empty cache.
pub(crate) fn remove_last(&mut self) -> T {
let last = self.cache.len() - 1;
let t = self.cache.remove(last);
self.lookup.remove(&t);
t
}
pub(crate) fn sorted(&self) -> IndexedCache<T> {
let mut sorted = Self::new();
self.cache.iter().sorted().cloned().for_each(|item| {
let n = sorted.cache.len();
sorted.cache.push(item.clone());
sorted.lookup.insert(item, n);
});
sorted
}
/// Create a vector from positions in this index to positions in an equivalent sorted index
///
/// This is useful primarily when encoding an `IndexedCache<ActorId>` in the document format.
/// In this case we encode the actors in sorted order in the document and all ops reference the
/// offset into this sorted actor array. But the `IndexedCache<ActorId>` we have in the
/// application does not contain actors in sorted order because we add them as we encounter
/// them, so we must map from the actor IDs in the application to the actor IDs in the document
/// format
///
/// # Examples
///
/// ```rust,ignore
/// let idx: IndexedCache<String> = IndexedCache::new();
/// let first_idx = idx.cache("b"); // first_idx is `0`
/// let second_idx = idx.cache("a"); // second_idx i `1`
/// let encoded = idx.encode_index();
/// // first_idx (0) maps to `1` whilst second_idx (1) maps to `0` because "a" < "b"
/// assert_eq!(encoded, vec![1,0])
/// ```
pub(crate) fn encode_index(&self) -> Vec<usize> {
let sorted: Vec<_> = self.cache.iter().sorted().cloned().collect();
self.cache
.iter()
.map(|a| sorted.iter().position(|r| r == a).unwrap())
.collect()
}
}
impl<T> IntoIterator for IndexedCache<T> {
type Item = T;
type IntoIter = std::vec::IntoIter<Self::Item>;
fn into_iter(self) -> Self::IntoIter {
self.cache.into_iter()
}
}
impl<T> Index<usize> for IndexedCache<T> {
type Output = T;
fn index(&self, i: usize) -> &T {
&self.cache[i]
}
}
impl<A: Hash + Eq + Clone> FromIterator<A> for IndexedCache<A> {
fn from_iter<T: IntoIterator<Item = A>>(iter: T) -> Self {
let mut cache = Vec::new();
let mut lookup = HashMap::new();
for (index, elem) in iter.into_iter().enumerate() {
cache.push(elem.clone());
lookup.insert(elem, index);
}
Self { cache, lookup }
}
}