import { State } from '../state';
import { ForeverCache } from './forever';

/**
 * ShortCache stores items in the cache for a short time.
 *
 * This cache can be a good choice if your server heavily relies
 * on HTTP cache headers and Ketting runs in your browser, or if in general
 * you want very up-to-date data.
 *
 * The reason in this scenarios it's useful to still have a 'very temporary'
 * cache, is because during many operations `get()` may be called in rapid
 * succession, and it also allows for enough time for 'embedded items' to
 * pe placed in the cache and extracted again.
 */
export class ShortCache extends ForeverCache {

  private cacheTimeout: number;
  private activeTimers: Map<string, ReturnType<typeof setInterval>>;

  /**
   * Create the short cache.
   *
   * cacheTimeout is specified in ms.
   */
  constructor(cacheTimeout: number = 30000) {
    super();
    this.cacheTimeout = cacheTimeout;
    this.activeTimers = new Map();
  }

  /**
   * Store a State object.
   *
   * This function will clone the state object before storing
   */
  store(state: State) {
    super.store(state);
    this.setTimer(state.uri);
  }

  private setTimer(uri: string) {

    if (this.activeTimers.has(uri)) {
      clearTimeout(this.activeTimers.get(uri)!);
    }
    // If there is a TON in the cache, this algorithm might
    // be optimized by using a linked list and a single timeout
    // for the 'next scheduled' expiry.
    //
    // The expectation is that this is not the case though, so this is the
    // lazy/easy way.
    this.activeTimers.set(
      uri,
      setTimeout( () => {
        this.delete(uri);
        this.activeTimers.delete(uri);
      }, this.cacheTimeout)
    );

  }

}