package org.javacs;

import java.nio.file.Path;

import java.time.Instant;

import java.util.HashMap;

import java.util.Map;

import java.util.Objects;

/** Cache maps a file + an arbitrary key to a value. When the file is modified, the mapping expires. */

class Cache<K, V> {

private static class Key<K> {

final Path file;

final K key;

Key(Path file, K key) {

this.file = file;

this.key = key;

}

@Override

public boolean equals(Object other) {

if (other.getClass() != Cache.Key.class) return false;

var that = (Cache.Key) other;

return Objects.equals(this.key, that.key) && Objects.equals(this.file, that.file);

}

@Override

public int hashCode() {

return Objects.hash(file, key);

}

}

private class Value {

final V value;

final Instant created = Instant.now();

Value(V value) {

this.value = value;

}

}

private final Map<Key, Value> map = new HashMap<>();

boolean has(Path file, K k) {

return !needs(file, k);

}

boolean needs(Path file, K k) {

// If key is not in map, it needs to be loaded

var key = new Key<K>(file, k);

if (!map.containsKey(key)) return true;

// If key was loaded before file was last modified, it needs to be reloaded

var value = map.get(key);

var modified = FileStore.modified(file);

if (modified == null) return true;

// TODO remove all keys associated with file when file changes

return value.created.isBefore(modified);

}

void load(Path file, K k, V v) {

// TODO limit total size of cache

var key = new Key<K>(file, k);

var value = new Value(v);

map.put(key, value);

}

V get(Path file, K k) {

var key = new Key<K>(file, k);

if (!map.containsKey(key)) {

throw new IllegalArgumentException(k + " is not in map " + map);

}

return map.get(key).value;

}

}