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import type { CacheOptions, ResourceCache } from "./types";
interface Job<T> {
promise: Promise<T>;
started: boolean;
force: boolean;
}
interface State<T> {
controller: AbortController;
entry?: Entry<T>;
// A scope token distinguishes inherited clear barriers from later per-key cleanup.
blocked: boolean | object;
job?: Job<T>;
queued?: Promise<T>;
}
function abortError() {
return new DOMException("Cache operation aborted", "AbortError");
}
// Rejection handlers stay attached even after cancellation: a host may ignore
// AbortSignal and settle its request much later.
function wait<T>(promise: Promise<T>, lifetime: AbortSignal, caller?: AbortSignal): Promise<T> {
const signals = caller ? [lifetime, caller] : [lifetime];
return new Promise<T>((resolve, reject) => {
const cleanup = () => {
for (const signal of signals) signal.removeEventListener("abort", abort);
};
const abort = () => {
cleanup();
reject(abortError());
};
for (const signal of signals) signal.addEventListener("abort", abort, { once: true });
promise.then(
(value) => {
cleanup();
resolve(value);
},
(error) => {
cleanup();
reject(error);
},
);
});
}
/** @internal */
export function validateOptions<T, Q>(options: CacheOptions<T, Q>): void {
if (typeof options.namespace !== "string" || !options.namespace.trim())
throw new TypeError("namespace must be nonempty");
if (!Number.isSafeInteger(options.schemaVersion) || options.schemaVersion <= 0)
throw new TypeError("schemaVersion must be a positive safe integer");
if (!Number.isFinite(options.maxAge) || options.maxAge < 0)
throw new TypeError("maxAge must be finite and nonnegative");
for (const name of ["key", "decode", "load"] as const) {
if (typeof options[name] !== "function") throw new TypeError(`${name} must be a function`);
}
}
/** @internal */
export function createCache<T, Q>(
options: CacheOptions<T, Q>,
backend: StorageBackend,
session: boolean,
): ResourceCache<T, Q> {
const states = new Map<string, State<T>>();
let disposed = false;
let scopeBlocked: false | object = false;
let disposal: Promise<void> | undefined;
let io: Promise<unknown> = Promise.resolve();
// Queue storage work, not network work. A removal is ordered after writes
// already submitted, and every later write checks its lifetime inside the queue.
function storage<R>(action: () => Promise<R>): Promise<R> {
const result = io.then(action);
io = result.catch(() => {});
return result;
}
function checkOpen() {
if (disposed) throw new Error("Cache is disposed");
}
function identity(query: Q): string {
checkOpen();
const key = options.key(query);
if (typeof key !== "string") throw new TypeError("key must return a string");
return key;
}
function stateFor(key: string): State<T> {
let state = states.get(key);
if (!state) {
state = { controller: new AbortController(), blocked: scopeBlocked };
states.set(key, state);
}
return state;
}
function checkState(state: State<T>) {
if (state.controller.signal.aborted) throw abortError();
}
function fresh(entry: Entry<T>): boolean {
const now = Date.now();
return !entry.invalidated && entry.validatedAt <= now && now - entry.validatedAt < options.maxAge;
}
function restore(value: Stored, previous?: Entry<T>): Entry<T> {
return { ...value.meta, data: value.body ? options.decode(value.body.data) : (previous as Entry<T>).data };
}
async function read(key: string, state: State<T>): Promise<Entry<T> | undefined> {
if (state.entry && fresh(state.entry)) return state.entry;
const entry = await storage(async () => {
checkState(state);
if (state.blocked) return state.entry;
try {
const value = await backend.read(key, state.entry?.version);
return value ? restore(value, state.entry) : state.entry;
} catch {
return state.entry;
}
});
checkState(state);
state.entry = entry;
return entry;
}
function schedule(key: string, query: Q, state: State<T>, force: boolean): Job<T> {
const job = { started: false, force } as Job<T>;
job.promise = (async () => {
const previous = await read(key, state);
checkState(state);
if (!job.force && previous && fresh(previous)) return previous.data;
job.started = true;
const result = await options.load(query, { etag: previous?.etag ?? null, signal: state.controller.signal });
checkState(state);
let entry: Entry<T>;
if (result.modified) {
entry = {
data: result.data,
etag: result.etag,
version: crypto.getRandomValues(new Uint32Array(4)).join("-"),
validatedAt: Date.now(),
invalidated: false,
};
} else {
if (!previous) throw new Error("Load protocol error: unmodified response without cached data");
entry = {
...previous,
etag: result.etag === undefined ? previous.etag : result.etag,
validatedAt: Date.now(),
invalidated: false,
};
}
await storage(async () => {
checkState(state);
try {
if (await backend.write(key, entry, result.modified)) state.blocked = false;
} catch {
// Retain the successful in-memory version. Old storage must not replace
// a response that could not be persisted, or bypass failed cleanup.
state.blocked = true;
}
checkState(state);
state.entry = entry;
});
checkState(state);
return entry.data;
})();
state.job = job;
// Registered before queued continuations, so the slot is released before
// any next round starts, on either outcome.
const release = () => {
state.job = undefined;
};
job.promise.then(release, release);
return job;
}
function refresh(key: string, query: Q, state: State<T>, force: boolean): Promise<T> {
const active = state.job;
if (!active) return schedule(key, query, state, force).promise;
if (!force) return active.promise;
if (!active.started) {
active.force = true;
return active.promise;
}
if (!state.queued) {
const start = () => {
checkState(state);
state.queued = undefined;
return schedule(key, query, state, true).promise;
};
state.queued = active.promise.then(start, start);
}
return state.queued;
}
// Publish the new lifetime first. Notify host abort listeners only after the
// operation has queued its cleanup; listeners may synchronously call back in.
function reset(key: string, keep: boolean) {
const old = states.get(key);
const state: State<T> = { controller: new AbortController(), blocked: true };
if (keep && old?.entry) state.entry = { ...old.entry, invalidated: true };
states.set(key, state);
return { state, cancel: () => old?.controller.abort() };
}
function resetAll() {
const old = [...states.values()];
states.clear();
const barrier = {};
scopeBlocked = barrier;
return {
barrier,
cancel() {
for (const state of old) state.controller.abort();
},
};
}
return {
async get(query, getOptions = {}) {
const key = identity(query);
if (getOptions.signal?.aborted) throw abortError();
const state = stateFor(key);
if (!getOptions.revalidate && state.entry && fresh(state.entry)) return state.entry.data;
return wait(
refresh(key, query, state, getOptions.revalidate === true),
state.controller.signal,
getOptions.signal,
);
},
async peek(query) {
const key = identity(query);
const state = stateFor(key);
const entry = await wait(read(key, state), state.controller.signal);
return entry
? { data: entry.data, etag: entry.etag, validatedAt: entry.validatedAt, fresh: fresh(entry) }
: undefined;
},
async invalidate(query) {
const key = identity(query);
const canRestore = !(states.get(key)?.blocked ?? scopeBlocked);
const { state, cancel } = reset(key, true);
const cleanup = storage(async () => {
const value = await backend.invalidate(key);
if (canRestore) state.blocked = false;
if (canRestore && !state.controller.signal.aborted && !state.entry && value) {
try {
state.entry = restore(value);
} catch {
/* Invalid stored bodies remain misses. */
}
}
});
cancel();
await cleanup;
},
async remove(query) {
const key = identity(query);
const { state, cancel } = reset(key, false);
const cleanup = storage(async () => {
await backend.remove(key);
state.blocked = false;
});
cancel();
await cleanup;
},
async clear() {
checkOpen();
const { barrier, cancel } = resetAll();
const cleanup = storage(async () => {
await backend.clear(false);
if (scopeBlocked === barrier) scopeBlocked = false;
for (const state of states.values()) {
if (state.blocked === barrier) state.blocked = false;
}
});
cancel();
await cleanup;
},
dispose() {
if (!disposal) {
disposed = true;
const { cancel } = resetAll();
disposal = storage(async () => {
if (session) await backend.clear(true);
});
disposal = disposal.catch((error) => {
disposal = undefined;
throw error;
});
cancel();
}
return disposal;
},
};
}
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