import { ICache } from './ICache';

import Debug from 'debug';

const debug = Debug('layer-cache:onion');

type OnionCacheConstructor = new (...caches: ICache[]) => ICache;

class OnionCacheImpl implements ICache {

caches: ICache[]

constructor(...caches: ICache[]) {

this.caches = caches;

}

async get(key: string): Promise<string> {

debug('get %s', key);

return this.__get(key, 0);

}

private async __get(key: string, index: number): Promise<string> {

if (index >= this.caches.length) {

return undefined;

}

const cache = this.caches[index];

const result = await cache.get(key);

if (!result) {

return this.__get(key, index + 1);

}

await this.__update(key, result, index - 1);

return result;

}

private async __update(key: string, value: string, index: number): Promise<void> {

if (index < 0) {

return;

}

const cache = this.caches[index];

await cache.set(key, value);

return this.__update(key, value, index - 1);

}

async set(key: string, value: string): Promise<void> {

debug('set %s', key);

return this.__set(key, value, 0);

}

private async __set(key: string, value: string, index: number): Promise<void> {

if (index >= this.caches.length) {

return;

}

const cache = this.caches[index];

await cache.set(key, value);

return this.__set(key, value, index + 1);

}

async del(key: string): Promise<void> {

debug('del %s', key);

return this.__del(key, 0);

}

private async __del(key: string, index: number): Promise<void> {

if (index >= this.caches.length) {

return;

}

const cache = this.caches[index];

await cache.del(key);

return this.__del(key, index + 1);

}

}

export const OnionCache: OnionCacheConstructor = OnionCacheImpl;