import assert from "assert";
import establishedDatabase from "../database/database";

class Cache {
  constructor(database) {
    this.database = database || establishedDatabase;
    this.queries = {
      read:
        'SELECT value, time_to_live, created_at, DATETIME("now", "localtime") as now, ' +
        'DATETIME(created_at, "+" || time_to_live || " seconds") as expires ' +
        "FROM cache WHERE key = ? AND now < expires",
      create:
        "INSERT OR REPLACE INTO cache (key, value, time_to_live) VALUES (?, ?, ?)"
    };
  }

  /**
   * Retrieve an unexpired cache entry by key.
   * @param {String} key of the cache entry
   * @returns {Object}
   */
  get(key) {
    return Promise.resolve()
      .then(() => this.database.get(this.queries.read, [key]))
      .then(row => {
        assert(row, "Could not find cache entry with that key.");
        return JSON.parse(row.value);
      });
  }

  /**
   * Insert cache entry with key and value.
   * @param {String} key of the cache entry
   * @param {String} value of the cache entry
   * @param {Number} timeToLive the number of seconds before entry expires
   * @returns {Object}
   */
  set(key, value, timeToLive = 10800) {
    const json = JSON.stringify(value);
    return Promise.resolve()
      .then(() =>
        this.database.run(this.queries.create, [key, json, timeToLive])
      )
      .then(() => value);
  }
}

export default Cache;