adapted.ts

import {JsonCompatible, JsonValue} from '@croct/json';
import {hasher, HasherOptions} from 'node-object-hash';
import {CacheLoader, CacheProvider} from './cacheProvider';

export type Transformer<D, S> = (value: D) => Promise<S> | S;

export type HashAlgorithm = 'passthrough' | 'md5' | 'sha1';

const HASHER = hasher({
    // Support classes and instances like `ResourceId`
    coerce: true,

    // Do not differentiate Objects, Sets and Maps constructed in different order
    // `new Set([1,2,3])` should match `new Set([3,2,1])`
    sort: {
        array: false,
        typedArray: false,
        object: true,
        set: true,
        map: true,
        bigint: true,
    },

    // Do not trim values, "foo " and "foo" should not match as the same key
    trim: false,
});

type Configuration<K, V, IK, IV> = {
    cache: CacheProvider<IK, IV>,
    keyTransformer: Transformer<K, IK>,
    valueInputTransformer: Transformer<V, IV>,
    valueOutputTransformer: Transformer<IV, V>,
};

function identity<T>(value: T): T {
    return value;
}

/**
 * A cache provider to transform keys and values between composition layers.
 */
export class AdaptedCache<K, V, IK = K, IV = V> implements CacheProvider<K, V> {
    private readonly cache: CacheProvider<IK, IV>;

    private readonly keyTransformer: Transformer<K, IK>;

    private readonly valueInputTransformer: Transformer<V, IV>;

    private readonly valueOutputTransformer: Transformer<IV, V>;

    public constructor(config: Configuration<K, V, IK, IV>) {
        this.cache = config.cache;
        this.keyTransformer = config.keyTransformer;
        this.valueInputTransformer = config.valueInputTransformer;
        this.valueOutputTransformer = config.valueOutputTransformer;
    }

    public static transformKeys<K, IK, V>(
        cache: CacheProvider<IK, V>,
        keyTransformer: Transformer<K, IK>,
    ): AdaptedCache<K, V, IK, V> {
        return new AdaptedCache({
            cache: cache,
            keyTransformer: keyTransformer,
            valueInputTransformer: identity,
            valueOutputTransformer: identity,
        });
    }

    public static transformValues<K, V, IV>(
        cache: CacheProvider<K, IV>,
        inputTransformer: Transformer<V, IV>,
        outputTransformer: Transformer<IV, V>,
    ): AdaptedCache<K, V, K, IV> {
        return new AdaptedCache({
            cache: cache,
            keyTransformer: identity,
            valueInputTransformer: inputTransformer,
            valueOutputTransformer: outputTransformer,
        });
    }

    public async get(key: K, loader: CacheLoader<K, V>): Promise<V> {
        return this.cache
            .get(
                await this.keyTransformer(key),
                () => loader(key).then(this.valueInputTransformer),
            )
            .then(this.valueOutputTransformer);
    }

    public async set(key: K, value: V): Promise<void> {
        return this.cache.set(
            await this.keyTransformer(key),
            await this.valueInputTransformer(value),
        );
    }

    public async delete(key: K): Promise<void> {
        return this.cache.delete(await this.keyTransformer(key));
    }

    public static createHashSerializer(algorithm?: HashAlgorithm): Transformer<any, string> {
        if (algorithm === 'passthrough') {
            // Do not hash when algorithm is set to `passthrough`
            return HASHER.sort.bind(HASHER);
        }

        const options: HasherOptions = {
            enc: 'base64',
            alg: algorithm,
        };

        return (value: any): string => HASHER.hash(value, options);
    }

    /**
     * Serializes a JSON compatible value to a string using JSON.stringify.
     *
     * This is a helper function for type safety.
      */
    public static jsonSerializer<T extends JsonCompatible>(): Transformer<T, string> {
        return JSON.stringify;
    }

    /**
     * Deserializes a string into a JSON value using JSON.parse.
     *
     * This is a helper function for type safety.
      */
    public static jsonDeserializer<T extends JsonValue>(): Transformer<string, T> {
        return JSON.parse;
    }
}