// @flow

import type {MousePanHandler} from '../mouse.js';
import type TouchPanHandler from './../touch_pan.js';

export type DragPanOptions = {
    linearity?: number;
    easing?: (t: number) => number;
    deceleration?: number;
    maxSpeed?: number;
};

/**
 * The `DragPanHandler` allows the user to pan the map by clicking and dragging
 * the cursor.
 *
 * @see [Example: Toggle interactions](https://docs.mapbox.com/mapbox-gl-js/example/toggle-interaction-handlers/)
 * @see [Example: Highlight features within a bounding box](https://docs.mapbox.com/mapbox-gl-js/example/using-box-queryrenderedfeatures/)
 */
export default class DragPanHandler {

    _el: HTMLElement;
    _mousePan: MousePanHandler;
    _touchPan: TouchPanHandler;
    _inertiaOptions: DragPanOptions

    /**
     * @private
    */
    constructor(el: HTMLElement, mousePan: MousePanHandler, touchPan: TouchPanHandler) {
        this._el = el;
        this._mousePan = mousePan;
        this._touchPan = touchPan;
    }

    /**
     * Enables the "drag to pan" interaction and accepts options to control the behavior of the panning inertia.
     *
     * @param {Object} [options] Options object.
     * @param {number} [options.linearity=0] Factor used to scale the drag velocity.
     * @param {Function} [options.easing] Optional easing function applied to {@link Map#panTo} when applying the drag. Defaults to bezier function using [@mapbox/unitbezier](https://github.com/mapbox/unitbezier).
     * @param {number} [options.maxSpeed=1400] The maximum value of the drag velocity.
     * @param {number} [options.deceleration=2500] The rate at which the speed reduces after the pan ends.
     *
     * @example
     * map.dragPan.enable();
     * @example
     * map.dragPan.enable({
     *     linearity: 0.3,
     *     easing: t => t,
     *     maxSpeed: 1400,
     *     deceleration: 2500
     * });
     * @see [Example: Highlight features within a bounding box](https://docs.mapbox.com/mapbox-gl-js/example/using-box-queryrenderedfeatures/)
     */
    enable(options?: DragPanOptions) {
        this._inertiaOptions = options || {};
        this._mousePan.enable();
        this._touchPan.enable();
        this._el.classList.add('mapboxgl-touch-drag-pan');
    }

    /**
     * Disables the "drag to pan" interaction.
     *
     * @example
     * map.dragPan.disable();
     */
    disable() {
        this._mousePan.disable();
        this._touchPan.disable();
        this._el.classList.remove('mapboxgl-touch-drag-pan');
    }

    /**
     * Returns a Boolean indicating whether the "drag to pan" interaction is enabled.
     *
     * @returns {boolean} Returns `true` if the "drag to pan" interaction is enabled.
     * @example
     * const isDragPanEnabled = map.dragPan.isEnabled();
     */
    isEnabled(): boolean {
        return this._mousePan.isEnabled() && this._touchPan.isEnabled();
    }

    /**
     * Returns a Boolean indicating whether the "drag to pan" interaction is active (currently being used).
     *
     * @returns {boolean} Returns `true` if the "drag to pan" interaction is active.
     * @example
     * const isDragPanActive = map.dragPan.isActive();
     */
    isActive(): boolean {
        return this._mousePan.isActive() || this._touchPan.isActive();
    }
}