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import { LitElement, property } from "lit-element";

import type { Constructor, Point2D } from "./utils";

function shouldSkipEvent(ev: TouchEvent): boolean {
  return ev.touches.length === 0 || ev.touches.length > 2;
}

function getDistance(a: Point2D, b: Point2D): number {
  return Math.sqrt(Math.pow(a.x - b.x, 2) + Math.pow(a.y - b.y, 2));
}

export interface TouchGestureMixinProps {
  isTouching: boolean;

  onTouchPan(delta: Point2D): void;
  onTouchPinch(delta: number): void;
}

export const TouchGestureMixin = <T extends Constructor<LitElement>>(
  superClass: T
): T & Constructor<TouchGestureMixinProps> =>
  class CTouchGesture extends superClass {
    private previousTouches: TouchList | null = null;

    constructor(...args: any[]) {
      super(...args);

      this.addEventListener("touchstart", (ev) => {
        if (shouldSkipEvent(ev)) {
          return;
        }

        ev.preventDefault();
        this.previousTouches = ev.touches;
      });

      this.addEventListener("touchend", (ev) => {
        if (shouldSkipEvent(ev)) {
          return;
        }

        ev.preventDefault();
        this.previousTouches = null;
      });

      this.addEventListener("touchcancel", (ev) => {
        if (shouldSkipEvent(ev)) {
          return;
        }

        ev.preventDefault();
        this.previousTouches = null;
      });

      this.addEventListener("touchmove", (ev) => {
        if (shouldSkipEvent(ev)) {
          return;
        }

        const previousTouches = Array.from(this.previousTouches || []);
        const currentTouches = Array.from(ev.touches);
        this.previousTouches = ev.touches;

        // When one or more than one of touch input sources differs, skip processing.
        if (
          currentTouches.length !== previousTouches.length ||
          !currentTouches.every((t) =>
            previousTouches.some((pt) => pt.identifier === t.identifier)
          )
        ) {
          return;
        }

        // Pan
        if (currentTouches.length === 1) {
          this.onTouchPan({
            x: currentTouches[0].pageX - previousTouches[0].pageX,
            y: currentTouches[0].pageY - previousTouches[0].pageY,
          });
          return;
        }

        // Pinch
        this.onTouchPinch(
          getDistance(
            {
              x: currentTouches[0].pageX,
              y: currentTouches[0].pageY,
            },
            {
              x: previousTouches[0].pageX,
              y: previousTouches[0].pageY,
            }
          )
        );
        return;
      });
    }

    get isTouching() {
      return !!(this.previousTouches && this.previousTouches.length > 0);
    }

    onTouchPan(delta: Point2D) {}
    onTouchPinch(delta: number) {}
  };