StoreCache.ts

import IStoreWriter from './IStoreWriter';
import IStoreReader from './IStoreReader';

export default class StoreCache implements IStoreWriter, IStoreReader {
  cache: { [key: number]: string }
  writer: IStoreWriter;
  reader: IStoreReader;

  constructor(_writer: IStoreWriter, _reader: IStoreReader) {
    this.cache = {}
    this.writer = _writer
    this.reader = _reader
  }

  public save(id: number, message: string): void {
    this.writer.save(id, message)
    this.addOrUpdate(id, message);
  }

  public read(id: number) {
    if(this.exists(id)) {
      return this.cache[id];
    }
    var retValue = this.reader.read(id);
    if(retValue !== undefined) {
      this.addOrUpdate(id, retValue);
    }
    return retValue;
  }

  private exists?(id: number): boolean {
    return this.cache.hasOwnProperty(id);
  }

  private addOrUpdate(id: number, message: string) {
    this.cache[id] = message;
  }
}