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

import {Trait} from '../trait';
import {TraitUpdatePositionedPositionPacket} from '../packets/trait-update-positioned-position.packet';

const decorate = compose(
  EventEmitter,
  Vector.Mixin('_position', 'x', 'y', {
    track: true,
  }),
  Vector.Mixin('serverPosition', 'serverX', 'serverY', {
    track: true,
  }),
);

// < 16768 will pack into 1 short per axe and give +/- 0.25 precision.
export class Positioned extends decorate(Trait) {

  static defaultState() {
    return {
      x: 0,
      y: 0,
    };
  }

  static type() {
    return 'positioned';
  }

  constructor(entity, params, state) {
    super(entity, params, state);
    this.on('_positionChanged', this.on_positionChanged, this);
    const x = this.state.x;
    const y = this.state.y;
    this._position = [x, y];
    this.entity.position[0] = x;
    this.entity.position[1] = y;
    if (AVOCADO_CLIENT) {
      this._relaxServerPositionConstraintIfNearerThan = 0;
      this.serverPosition = this._position;
      this.serverPositionDirty = false;
      this.on('serverPositionChanged', this.onServerPositionChanged, this);
    }
  }

  destroy() {
    this.off('_positionChanged', this.on_positionChanged);
    if (AVOCADO_CLIENT) {
      this.off('serverPositionChanged', this.onServerPositionChanged);
    }
  }

  acceptPacket(packet) {
    if (packet instanceof TraitUpdatePositionedPositionPacket) {
      [this.serverX, this.serverY] = packet.data.position;
    }
  }

  on_positionChanged(oldPosition, newPosition) {
    this.entity.position[0] = newPosition[0];
    this.entity.position[1] = newPosition[1];
    if (AVOCADO_SERVER) {
      this.state.x = newPosition[0];
      this.state.y = newPosition[1];
    }
    this.entity.emit('positionChanged', oldPosition, newPosition);
  }

  onServerPositionChanged() {
    this.serverPositionDirty = true;
  }

  packets(informed) {
    const {x, y} = this.stateDifferences();
    if (x || y) {
      // Physics slop can end us up with negatives. Don't allow them in the
      // packed representation, even though it means a slight loss in accuracy.
      // The world bounds will (should!) keep things *eventually* correct.
      const x = Math.max(0, this.state.x);
      const y = Math.max(0, this.state.y);
      return new TraitUpdatePositionedPositionPacket({
        position: [x, y],
      });
    }
  }

  set relaxServerPositionConstraintIfNearerThan(nearerThan) {
    this._relaxServerPositionConstraintIfNearerThan = nearerThan;
  }

  listeners() {
    return {

      isTickingChanged: () => {
        // Snap position on ticking change.
        if (AVOCADO_CLIENT) {
          this._position = this.serverPosition;
        }
      },

    };
  }

  methods() {
    return {

      setPosition: (position) => {
        this._position = position;
      },

    };
  }

  renderTick(elapsed) {
    if (!this.serverPositionDirty) {
      return;
    }
    if (Vector.equals(this._position, this.serverPosition)) {
      this.serverPositionDirty = false;
      return;
    }
    if (Vector.equalsClose(this._position, this.serverPosition, 0.1)) {
      this._position = this.serverPosition;
      this.serverPositionDirty = false;
      return;
    }
    const diff = Vector.sub(this.serverPosition, this._position);
    const nearerThan = this._relaxServerPositionConstraintIfNearerThan;
    let lerp;
    if (
      nearerThan
      && Vector.equalsClose(this._position, this.serverPosition, nearerThan)
    ) {
      lerp = .01;
    }
    else {
      lerp = .5;
    }
    this._position = Vector.add(this._position, Vector.scale(diff, lerp));
  }

}