indexed-collection.ts

import { Map } from 'immutable';

import { IResource, IResourceId } from 'dto/resource';
import { optionalFindIndex } from '../common/utility/optional-find-index';

class IndexedCollection<R extends IResource<R>> {

  constructor(
    private readonly items: R[],
    private readonly indexed: Map<IResourceId<R>, R>,
  ) {}

  public set(id: IResourceId<R>, item: R) {
    return new IndexedCollection(
      optionalFindIndex(this.items, ({ id }) => id === item.id)
        .cata(
          () => this.items.concat(item),
          index => this.items
            .slice(0, index - 1)
            .concat(item)
            .concat(this.items.slice(index))),
      this.indexed.set(id, item),
    );
  }

  public update(id: IResourceId<R>, updater: (item: R) => R) {
    return new IndexedCollection(
      this.items.map(item => item.id === id ? updater(item) : item),
      this.indexed.has(id) ? this.indexed.update(id, updater) : this.indexed,
    );
  }

  public feed(items: R[]) {
    return new IndexedCollection(
      items.slice(),
      items.reduce((indexed, item) => indexed.set(item.id, item), this.indexed),
    );
  }

}