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use fx::FxHashMap;
use std::hash::Hash;
use std::ops;
use std::mem;
#[cfg(test)]
mod test;
pub struct SnapshotMap<K, V>
where K: Hash + Clone + Eq
{
map: FxHashMap<K, V>,
undo_log: Vec<UndoLog<K, V>>,
}
pub struct Snapshot {
len: usize,
}
enum UndoLog<K, V> {
OpenSnapshot,
CommittedSnapshot,
Inserted(K),
Overwrite(K, V),
Noop,
}
impl<K, V> SnapshotMap<K, V>
where K: Hash + Clone + Eq
{
pub fn new() -> Self {
SnapshotMap {
map: FxHashMap(),
undo_log: vec![],
}
}
pub fn clear(&mut self) {
self.map.clear();
self.undo_log.clear();
}
pub fn insert(&mut self, key: K, value: V) -> bool {
match self.map.insert(key.clone(), value) {
None => {
if !self.undo_log.is_empty() {
self.undo_log.push(UndoLog::Inserted(key));
}
true
}
Some(old_value) => {
if !self.undo_log.is_empty() {
self.undo_log.push(UndoLog::Overwrite(key, old_value));
}
false
}
}
}
pub fn insert_noop(&mut self) {
if !self.undo_log.is_empty() {
self.undo_log.push(UndoLog::Noop);
}
}
pub fn remove(&mut self, key: K) -> bool {
match self.map.remove(&key) {
Some(old_value) => {
if !self.undo_log.is_empty() {
self.undo_log.push(UndoLog::Overwrite(key, old_value));
}
true
}
None => false,
}
}
pub fn get(&self, key: &K) -> Option<&V> {
self.map.get(key)
}
pub fn snapshot(&mut self) -> Snapshot {
self.undo_log.push(UndoLog::OpenSnapshot);
let len = self.undo_log.len() - 1;
Snapshot { len: len }
}
fn assert_open_snapshot(&self, snapshot: &Snapshot) {
assert!(snapshot.len < self.undo_log.len());
assert!(match self.undo_log[snapshot.len] {
UndoLog::OpenSnapshot => true,
_ => false,
});
}
pub fn commit(&mut self, snapshot: Snapshot) {
self.assert_open_snapshot(&snapshot);
if snapshot.len == 0 {
self.undo_log.truncate(0);
} else {
self.undo_log[snapshot.len] = UndoLog::CommittedSnapshot;
}
}
pub fn partial_rollback<F>(&mut self,
snapshot: &Snapshot,
should_revert_key: &F)
where F: Fn(&K) -> bool
{
self.assert_open_snapshot(snapshot);
for i in (snapshot.len + 1..self.undo_log.len()).rev() {
let reverse = match self.undo_log[i] {
UndoLog::OpenSnapshot => false,
UndoLog::CommittedSnapshot => false,
UndoLog::Noop => false,
UndoLog::Inserted(ref k) => should_revert_key(k),
UndoLog::Overwrite(ref k, _) => should_revert_key(k),
};
if reverse {
let entry = mem::replace(&mut self.undo_log[i], UndoLog::Noop);
self.reverse(entry);
}
}
}
pub fn rollback_to(&mut self, snapshot: Snapshot) {
self.assert_open_snapshot(&snapshot);
while self.undo_log.len() > snapshot.len + 1 {
let entry = self.undo_log.pop().unwrap();
self.reverse(entry);
}
let v = self.undo_log.pop().unwrap();
assert!(match v {
UndoLog::OpenSnapshot => true,
_ => false,
});
assert!(self.undo_log.len() == snapshot.len);
}
fn reverse(&mut self, entry: UndoLog<K, V>) {
match entry {
UndoLog::OpenSnapshot => {
panic!("cannot rollback an uncommitted snapshot");
}
UndoLog::CommittedSnapshot => {}
UndoLog::Inserted(key) => {
self.map.remove(&key);
}
UndoLog::Overwrite(key, old_value) => {
self.map.insert(key, old_value);
}
UndoLog::Noop => {}
}
}
}
impl<'k, K, V> ops::Index<&'k K> for SnapshotMap<K, V>
where K: Hash + Clone + Eq
{
type Output = V;
fn index(&self, key: &'k K) -> &V {
&self.map[key]
}
}