import { ICache } from './ICache';

import Debug from 'debug';

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

type FillFunction = (key: string) => Promise<string>

type NonSerializingCacheConstructor = new (cache: ICache, fillFn: FillFunction) => ICache;

class NonSerializingCacheImpl implements ICache {

cache: ICache

fillFn: FillFunction

constructor(cache: ICache, fillFn: FillFunction) {

this.cache = cache;

this.fillFn = fillFn;

}

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

debug("Getting '%s'", key);

let result = await this.cache.get(key);

if (result === undefined) {

try {

result = await this.fillFn(key);

} catch (err) {

debug("Fill '%s' failed", key);

throw err;

}

try {

await this.cache.set(key, result);

debug("Storing '%s' successful", key);

} catch (err) {

debug("Storing '%s' failed: %s", key);

throw err;

}

}

debug("Get '%s' successful", key);

return result;

}

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

throw new Error("Set is not implemented")

}

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

debug("Deleting '%s'", key);

return this.cache.del(key);

}

}

export const NonSerializingCache: NonSerializingCacheConstructor = NonSerializingCacheImpl;