/**
 * @module ol/interaction/Pointer
 */
import Interaction from './Interaction.js';
import MapBrowserEventType from '../MapBrowserEventType.js';

/**
 * @typedef {Object} Options
 * @property {function(import("../MapBrowserEvent.js").default):boolean} [handleDownEvent]
 * Function handling "down" events. If the function returns `true` then a drag
 * sequence is started.
 * @property {function(import("../MapBrowserEvent.js").default):void} [handleDragEvent]
 * Function handling "drag" events. This function is called on "move" events
 * during a drag sequence.
 * @property {function(import("../MapBrowserEvent.js").default):boolean} [handleEvent]
 * Method called by the map to notify the interaction that a browser event was
 * dispatched to the map. The function may return `false` to prevent the
 * propagation of the event to other interactions in the map's interactions
 * chain.
 * @property {function(import("../MapBrowserEvent.js").default):void} [handleMoveEvent]
 * Function handling "move" events. This function is called on "move" events.
 * This functions is also called during a drag sequence, so during a drag
 * sequence both the `handleDragEvent` function and this function are called.
 * If `handleDownEvent` is defined and it returns true this function will not
 * be called during a drag sequence.
 * @property {function(import("../MapBrowserEvent.js").default):boolean} [handleUpEvent]
 *  Function handling "up" events. If the function returns `false` then the
 * current drag sequence is stopped.
 * @property {function(boolean):boolean} [stopDown]
 * Should the down event be propagated to other interactions, or should be
 * stopped?
 */

/**
 * @classdesc
 * Base class that calls user-defined functions on `down`, `move` and `up`
 * events. This class also manages "drag sequences".
 *
 * When the `handleDownEvent` user function returns `true` a drag sequence is
 * started. During a drag sequence the `handleDragEvent` user function is
 * called on `move` events. The drag sequence ends when the `handleUpEvent`
 * user function is called and returns `false`.
 * @api
 */
class PointerInteraction extends Interaction {
  /**
   * @param {Options} [options] Options.
   */
  constructor(options) {
    options = options ? options : {};

    super(
      /** @type {import("./Interaction.js").InteractionOptions} */ (options)
    );

    if (options.handleDownEvent) {
      this.handleDownEvent = options.handleDownEvent;
    }

    if (options.handleDragEvent) {
      this.handleDragEvent = options.handleDragEvent;
    }

    if (options.handleMoveEvent) {
      this.handleMoveEvent = options.handleMoveEvent;
    }

    if (options.handleUpEvent) {
      this.handleUpEvent = options.handleUpEvent;
    }

    if (options.stopDown) {
      this.stopDown = options.stopDown;
    }

    /**
     * @type {boolean}
     * @protected
     */
    this.handlingDownUpSequence = false;

    /**
     * @type {Array<PointerEvent>}
     * @protected
     */
    this.targetPointers = [];
  }

  /**
   * Returns the current number of pointers involved in the interaction,
   * e.g. `2` when two fingers are used.
   * @return {number} The number of pointers.
   * @api
   */
  getPointerCount() {
    return this.targetPointers.length;
  }

  /**
   * Handle pointer down events.
   * @param {import("../MapBrowserEvent.js").default} mapBrowserEvent Event.
   * @return {boolean} If the event was consumed.
   * @protected
   */
  handleDownEvent(mapBrowserEvent) {
    return false;
  }

  /**
   * Handle pointer drag events.
   * @param {import("../MapBrowserEvent.js").default} mapBrowserEvent Event.
   * @protected
   */
  handleDragEvent(mapBrowserEvent) {}

  /**
   * Handles the {@link module:ol/MapBrowserEvent~MapBrowserEvent map browser event} and may call into
   * other functions, if event sequences like e.g. 'drag' or 'down-up' etc. are
   * detected.
   * @param {import("../MapBrowserEvent.js").default} mapBrowserEvent Map browser event.
   * @return {boolean} `false` to stop event propagation.
   * @api
   */
  handleEvent(mapBrowserEvent) {
    if (!mapBrowserEvent.originalEvent) {
      return true;
    }

    let stopEvent = false;
    this.updateTrackedPointers_(mapBrowserEvent);
    if (this.handlingDownUpSequence) {
      if (mapBrowserEvent.type == MapBrowserEventType.POINTERDRAG) {
        this.handleDragEvent(mapBrowserEvent);
        // prevent page scrolling during dragging
        mapBrowserEvent.originalEvent.preventDefault();
      } else if (mapBrowserEvent.type == MapBrowserEventType.POINTERUP) {
        const handledUp = this.handleUpEvent(mapBrowserEvent);
        this.handlingDownUpSequence =
          handledUp && this.targetPointers.length > 0;
      }
    } else {
      if (mapBrowserEvent.type == MapBrowserEventType.POINTERDOWN) {
        const handled = this.handleDownEvent(mapBrowserEvent);
        this.handlingDownUpSequence = handled;
        stopEvent = this.stopDown(handled);
      } else if (mapBrowserEvent.type == MapBrowserEventType.POINTERMOVE) {
        this.handleMoveEvent(mapBrowserEvent);
      }
    }
    return !stopEvent;
  }

  /**
   * Handle pointer move events.
   * @param {import("../MapBrowserEvent.js").default} mapBrowserEvent Event.
   * @protected
   */
  handleMoveEvent(mapBrowserEvent) {}

  /**
   * Handle pointer up events.
   * @param {import("../MapBrowserEvent.js").default} mapBrowserEvent Event.
   * @return {boolean} If the event was consumed.
   * @protected
   */
  handleUpEvent(mapBrowserEvent) {
    return false;
  }

  /**
   * This function is used to determine if "down" events should be propagated
   * to other interactions or should be stopped.
   * @param {boolean} handled Was the event handled by the interaction?
   * @return {boolean} Should the `down` event be stopped?
   */
  stopDown(handled) {
    return handled;
  }

  /**
   * @param {import("../MapBrowserEvent.js").default} mapBrowserEvent Event.
   * @private
   */
  updateTrackedPointers_(mapBrowserEvent) {
    if (mapBrowserEvent.activePointers) {
      this.targetPointers = mapBrowserEvent.activePointers;
    }
  }
}

/**
 * @param {Array<PointerEvent>} pointerEvents List of events.
 * @return {{clientX: number, clientY: number}} Centroid pixel.
 */
export function centroid(pointerEvents) {
  const length = pointerEvents.length;
  let clientX = 0;
  let clientY = 0;
  for (let i = 0; i < length; i++) {
    clientX += pointerEvents[i].clientX;
    clientY += pointerEvents[i].clientY;
  }
  return {clientX: clientX / length, clientY: clientY / length};
}

export default PointerInteraction;