import {compose, EventEmitter, Property} from '@avocado/core';
import {Rectangle, Vector} from '@avocado/math';

const decorate = compose(
  EventEmitter,
  Vector.Mixin('areaSize', 'areaWidth', 'areaHeight', {
    default: [0, 0],
    track: true,
  }),
  Property('drag', {
    default: 0.2,
  }),
  Vector.Mixin('position', 'x', 'y', {
    default: [0, 0],
  }),
  Vector.Mixin('realOffset', 'realOffsetX', 'realOffsetY', {
    default: [0, 0],
    track: true,
  }),
  Vector.Mixin('realPosition', 'realX', 'realY', {
    default: [0, 0],
    track: true,
  }),
  Vector.Mixin('viewSize', 'viewWidth', 'viewHeight', {
    default: [0, 0],
    track: true,
  }),
);

export class Camera extends decorate(class {}) {

  constructor() {
    super();
    this.viewOrigin = [0, 0];
    this.on('areaSizeChanged', this.onAreaSizeChanged, this);
    this.on('realPositionChanged', this.onRealPositionChanged, this);
    this.on('viewSizeChanged', this.onViewSizeChanged, this);
  }

  destroy() {
    this.off('areaSizeChanged', this.onAreaSizeChanged);
    this.off('realPositionChanged', this.onRealPositionChanged, this);
    this.off('viewSizeChanged', this.onViewSizeChanged);
  }

  onAreaSizeChanged() {
    this.position = this.position;
  }

  onRealPositionChanged() {
    this.realOffset = Vector.sub(this.realPosition, this.viewOrigin);
  }

  onViewSizeChanged() {
    this.position = this.position;
    this.viewOrigin = Vector.scale(this.viewSize, 0.5);
    this.realOffset = Vector.sub(this.realPosition, this.viewOrigin);
  }

  get position() {
    return super.position;
  }

  set position(position) {
    if (0 === Vector.area(this.areaSize)) {
      return super.position = position;
    }
    if (0 === Vector.area(this.viewSize)) {
      return super.position = position;
    }
    const viewOrigin = this.viewOrigin;
    super.position = Vector.clamp(
      position,
      viewOrigin,
      Vector.sub(this.areaSize, viewOrigin)
    );
  }

  get rectangle() {
    return Rectangle.compose(
      Vector.sub(this.position, this.viewOrigin),
      this.viewSize,
    );
  }

  tick(elapsed) {
    if (Vector.equals(this.position, this.realPosition)) {
      return;
    }
    if (0 === this.drag) {
      this.realPosition = this.position;
    }
    if (Vector.equalsClose(this.position, this.realPosition, 0.5)) {
      this.realPosition = this.position;
      return;
    }
    // Sanity check.
    const k = elapsed / this.drag;
    if (k >= 1) {
      this.realPosition = this.position;
      return;
    }
    const diff = Vector.sub(this.position, this.realPosition);
    const magnitude = Vector.scale(diff, k);
    this.realPosition = Vector.add(this.realPosition, magnitude);
  }

}