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type ScopedCacheOptions<T> = {
maxEntries?: number
ttlMs?: number
dispose?: (value: T, key: string) => void
now?: () => number
}
type Entry<T> = {
value: T
touchedAt: number
}
export function createScopedCache<T>(createValue: (key: string) => T, options: ScopedCacheOptions<T> = {}) {
const store = new Map<string, Entry<T>>()
const now = options.now ?? Date.now
const dispose = (key: string, entry: Entry<T>) => {
options.dispose?.(entry.value, key)
}
const expired = (entry: Entry<T>) => {
if (options.ttlMs === undefined) return false
return now() - entry.touchedAt >= options.ttlMs
}
const sweep = () => {
if (options.ttlMs === undefined) return
for (const [key, entry] of store) {
if (!expired(entry)) continue
store.delete(key)
dispose(key, entry)
}
}
const touch = (key: string, entry: Entry<T>) => {
entry.touchedAt = now()
store.delete(key)
store.set(key, entry)
}
const prune = () => {
if (options.maxEntries === undefined) return
while (store.size > options.maxEntries) {
const key = store.keys().next().value
if (!key) return
const entry = store.get(key)
store.delete(key)
if (!entry) continue
dispose(key, entry)
}
}
const remove = (key: string) => {
const entry = store.get(key)
if (!entry) return
store.delete(key)
dispose(key, entry)
return entry.value
}
const peek = (key: string) => {
sweep()
const entry = store.get(key)
if (!entry) return
if (!expired(entry)) return entry.value
store.delete(key)
dispose(key, entry)
}
const get = (key: string) => {
sweep()
const entry = store.get(key)
if (entry && !expired(entry)) {
touch(key, entry)
return entry.value
}
if (entry) {
store.delete(key)
dispose(key, entry)
}
const created = {
value: createValue(key),
touchedAt: now(),
}
store.set(key, created)
prune()
return created.value
}
const clear = () => {
for (const [key, entry] of store) {
dispose(key, entry)
}
store.clear()
}
return {
get,
peek,
delete: remove,
clear,
}
}
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