mancala/apps/backend/src/cache/Cache.ts

import { Valkey } from "iovalkey";

const PREFIX = "mancala:cache:";

// Short-lived cache of JSON values. Never fails: errors count as a miss, so callers just compute the value.
export interface Cache {
    getJson<T>(key: string): Promise<T | undefined>;
    setJson(key: string, value: unknown, ttlSeconds: number): Promise<void>;
    delete(...keys: string[]): Promise<void>;
}

export class ValkeyCache implements Cache {
    constructor(private readonly client: Valkey) { }

    async getJson<T>(key: string): Promise<T | undefined> {
        try {
            const value = await this.client.get(PREFIX + key);
            return value === null ? undefined : JSON.parse(value) as T;
        } catch (err) {
            return undefined;
        }
    }

    async setJson(key: string, value: unknown, ttlSeconds: number): Promise<void> {
        try {
            await this.client.set(PREFIX + key, JSON.stringify(value), "EX", ttlSeconds);
        } catch (err) {
            // A missing cache entry only costs a database query.
        }
    }

    async delete(...keys: string[]): Promise<void> {
        if (keys.length === 0) return;
        try {
            await this.client.del(...keys.map((key) => PREFIX + key));
        } catch (err) {
            // Entries expire on their own.
        }
    }
}