entity-command-reducer.ts

import { EntityAdapter, EntityState } from '@ngrx/entity';
import { ActionReducer } from '@ngrx/store';
import { CommandReducer, ReducerCommand } from 'ngrx-command-reducer';
import { BaseAction, StaticAction } from './base.actions';

type PayloadActionFunction<S, P> = (p: P, s: S) => S;
type PayloadlessActionFunction<S> = (s: S) => S;
export type EntityFunction<S, P> = PayloadActionFunction<S, P> | PayloadlessActionFunction<S>;

export class EntityCommandReducer<Entity, State extends EntityState<Entity>, Action extends BaseAction> {

  private commandReducer: CommandReducer<State, Action>;

  constructor(initialState: State, private adapter: EntityAdapter<Entity>) {
    this.commandReducer = new CommandReducer(initialState, a => a.payload);
  }

  public mapAction<Payload>(action: StaticAction<Payload, Action>,
                            adapterFunctionGetter: (adapter: EntityAdapter<Entity>) => EntityFunction<State, Payload>): this {

    const adapterFunction = adapterFunctionGetter(this.adapter);

    return this.add(action, (state: State, payload: Payload) => {

      if (this.isPayloadFunction(adapterFunction)) {
        return adapterFunction(payload, state);
      }

      return adapterFunction(state);
    });

  }

  public add<Payload>(action: StaticAction<Payload, Action>, handler: ReducerCommand<State, Payload>): this {

    this.commandReducer.add(action, handler);

    return this;
  }

  public reducer(): ActionReducer<State> {
    return this.commandReducer.reducer();
  }

  private isPayloadFunction<S, P>(fn: EntityFunction<S, P>): fn is PayloadActionFunction<S, P> {
    return fn.length === 2;
  }

}