import {compose, TickingPromise} from '@avocado/core';
import {EventEmitter} from '@avocado/mixins';

import {Traversal} from './traversal';
import {Traversals} from './traversals';

const decorate = compose(
  EventEmitter,
);

export class Actions extends decorate(Traversals) {

  constructor() {
    super();
    this._index = 0;
    this.traversals = [];
    this.pending = null;
  }

  emitFinished() {
    this.emit('actionsFinished');
  }

  get index() {
    return this._index;
  }

  set index(index) {
    this._index = index;
  }

  tick(context, elapsed) {
    if (this.traversals.length === 0) {
      this.emitFinished();
      return;
    }
    if (
      this.pending
      && this.pending instanceof TickingPromise
      && 'function' === typeof this.pending.ticker
    ) {
      this.pending.ticker(elapsed);
      return;
    }

    // Actions execute immediately until a promise is made, or they're all
    // executed.
    while (true) {
      const result = this.traversals[this.index].traverse(context);
      if (result instanceof Promise) {
        result.then(() => this.prologue());
        result.catch((error) => {
          throw error;
        });
        this.pending = result;
        break;
      }
      this.prologue();
      if (0 === this.index) {
        break;
      }
    }
  }

  prologue() {
    this.pending = null;
    if (0 === (this.index = (this.index + 1) % this.traversals.length)) {
      this.emitFinished();
    }
  }

}