import { Maybe, Stringified, stringify, parse } from '@dotstats/common';

export class Persistent<Data> {
  private readonly onChange: (value: Data) => void;
  private readonly key: string;
  private value: Data;

  constructor(key: string, initial: Data, onChange: (value: Data) => void) {
    this.key = key;
    this.onChange = onChange;

    const stored = window.localStorage.getItem(key) as Maybe<Stringified<Data>>;

    if (stored) {
      this.value = parse(stored);
    } else {
      this.value = initial;
    }

    window.addEventListener('storage', (event) => {
      if (event.key === this.key) {
        this.value = parse(event.newValue as any as Stringified<Data>);

        this.onChange(this.value);
      }
    });
  }

  public get(): Data {
    return this.value;
  }

  public set<K extends keyof Data>(changes: Pick<Data, K> | Data) {
    this.value = Object.assign({}, this.value, changes);
    window.localStorage.setItem(this.key, stringify(this.value) as any as string);
    this.onChange(this.value);
  }
}