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

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

const decorate = compose(
  EventEmitter,
);

export class Actions extends decorate(Traversals) {

  static type() {
    return 'actions';
  }

  constructor() {
    super();
    this._index = 0;
    this._actionPromise = null;
  }

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

  get index() {
    return this._index;
  }

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

  get() {
    return this;
  }

  tick(context, elapsed) {
    // Empty resolves immediately.
    if (this.traversals.length === 0) {
      this.emitFinished();
      return;
    }
    // If the action promise ticks, tick it.
    if (this._actionPromise && this._actionPromise instanceof TickingPromise) {
      this._actionPromise.tick(elapsed);
      return;
    }
    // Actions execute immediately until a promise is made, or they're all
    // executed.
    while (true) {
      // Run the action.
      const result = this.traversals[this.index].traverse(context);
      // Deferred result.
      if (result instanceof Promise) {
        this._actionPromise = result;
        // Handle any errors.
        result.catch(console.error);
        result.finally(() => {
          // Finally, run the prologue.
          this.prologue();
        });
        break;
      }
      // Immediate result.
      this.prologue();
      // Need to break out immediately if required.
      if (0 === this.index) {
        break;
      }
    }
  }

  parallel(context) {
    // Map all traversals to results.
    const results = this.traversals.map((traversal) => {
      return traversal.traverse(context);
    });
    // Wrap all results in a TickingPromise.
    return TickingPromise.all(results);
  }

  prologue() {
    // Clear out the action promise.
    this._actionPromise = null;
    // Increment and wrap the index.
    this.index = (this.index + 1) % this.traversals.length;
    // If rolled over, the actions are finished.
    if (0 === this.index) {
      this.emitFinished();
    }
  }

  serial(context) {
    return this.tickingPromise(context);
  }

  tickingPromise(context) {
    return new TickingPromise(
      (resolve) => {
        this.once('actionsFinished', resolve);
      },
      (elapsed) => {
        this.tick(context, elapsed);
      },
    );
  }

}