/**
 * A DragTracker listens for drag events on an Element and fires events at the start and end of the drag,
 * as well as during the drag. This is useful for components such as {@link Ext.slider.Multi}, where there is
 * an element that can be dragged around to change the Slider's value.
 *
 * DragTracker provides a series of template methods that should be overridden to provide functionality
 * in response to detected drag operations. These are onBeforeStart, onStart, onDrag and onEnd.
 * See {@link Ext.slider.Multi}'s initEvents function for an example implementation.
 */
Ext.define('Ext.dd.DragTracker', {

    uses: ['Ext.util.Region'],

    mixins: {
        observable: 'Ext.util.Observable'
    },

    /**
     * @property {Boolean} active
     * Indicates whether the user is currently dragging this tracker.
     * @readonly
     */
    active: false,

    /**
     * @property {HTMLElement} dragTarget
     * The element being dragged.
     *
     * Only valid during drag operations.
     *
     * If the {@link #delegate} option is used, this will be the delegate element which was mousedowned.
     * @readonly
     */

    /**
     * @cfg {Boolean} trackOver
     * Set to true to fire mouseover and mouseout events when the mouse enters or leaves the target element.
     *
     * This is implicitly set when an {@link #overCls} is specified.
     *
     * If the {@link #delegate} option is used, these events fire only when a delegate element is entered of left.
     */
    trackOver: false,

    /**
     * @cfg {String} overCls
     * A CSS class to add to the DragTracker's target element when the element (or, if the {@link #delegate}
     * option is used, when a delegate element) is mouseovered.
     *
     * If the {@link #delegate} option is used, these events fire only when a delegate element is entered of left.
     */

    /**
     * @cfg {Ext.util.Region/Ext.Element} constrainTo
     * A {@link Ext.util.Region Region} (Or an element from which a Region measurement will be read)
     * which is used to constrain the result of the {@link #getOffset} call.
     *
     * This may be set any time during the DragTracker's lifecycle to set a dynamic constraining region.
     */

    /**
     * @cfg {Number} tolerance
     * Number of pixels the drag target must be moved before dragging is
     * considered to have started.
     */
    tolerance: 5,

    /**
     * @cfg {Boolean/Number} autoStart
     * Specify `true` to defer trigger start by 1000 ms.
     * Specify a Number for the number of milliseconds to defer trigger start.
     */
    autoStart: false,

    /**
     * @cfg {String} delegate
     * A {@link Ext.DomQuery DomQuery} selector which identifies child elements within the DragTracker's encapsulating
     * Element which are the tracked elements. This limits tracking to only begin when the matching elements are mousedowned.
     *
     * This may also be a specific child element within the DragTracker's encapsulating element to use as the tracked element.
     */

    /**
     * @cfg {Boolean} [preventDefault=true]
     * Specify `false` to enable default actions on onMouseDown events.
     */

    /**
     * @cfg {Boolean} [stopEvent=false]
     * Specify `true` to stop the `mousedown` event from bubbling to outer listeners from the target element (or its delegates).
     */

    constructor : function(config){
        Ext.apply(this, config);
        this.addEvents(
            /**
             * @event mouseover
             * Fires when the mouse enters the DragTracker's target element (or if {@link #delegate} is
             * used, when the mouse enters a delegate element).
             *
             * **Only available when {@link #trackOver} is `true`**
             *
             * @param {Object} this
             * @param {Object} e event object
             * @param {HTMLElement} target The element mouseovered.
             */
            'mouseover',

            /**
             * @event mouseout
             * Fires when the mouse exits the DragTracker's target element (or if {@link #delegate} is
             * used, when the mouse exits a delegate element).
             * 
             * **Only available when {@link #trackOver} is `true`**
             *
             * @param {Object} this
             * @param {Object} e event object
             */
            'mouseout',

            /**
             * @event mousedown
             * Fires when the mouse button is pressed down, but before a drag operation begins. The
             * drag operation begins after either the mouse has been moved by {@link #tolerance} pixels,
             * or after the {@link #autoStart} timer fires.
             *
             * Return false to veto the drag operation.
             *
             * @param {Object} this
             * @param {Object} e event object
             */
            'mousedown',

            /**
             * @event mouseup
             * @param {Object} this
             * @param {Object} e event object
             */
            'mouseup',

            /**
             * @event mousemove
             * Fired when the mouse is moved. Returning false cancels the drag operation.
             * @param {Object} this
             * @param {Object} e event object
             */
            'mousemove',

            /**
             * @event beforestart
             * @param {Object} this
             * @param {Object} e event object
             */
            'beforedragstart',

            /**
             * @event dragstart
             * @param {Object} this
             * @param {Object} e event object
             */
            'dragstart',

            /**
             * @event dragend
             * @param {Object} this
             * @param {Object} e event object
             */
            'dragend',

            /**
             * @event drag
             * @param {Object} this
             * @param {Object} e event object
             */
            'drag'
        );

        this.dragRegion = new Ext.util.Region(0,0,0,0);

        if (this.el) {
            this.initEl(this.el);
        }

        // Dont pass the config so that it is not applied to 'this' again
        this.mixins.observable.constructor.call(this);
        if (this.disabled) {
            this.disable();
        }

    },

    /**
     * Initializes the DragTracker on a given element.
     * @param {Ext.Element/HTMLElement} el The element
     */
    initEl: function(el) {
        this.el = Ext.get(el);

        // The delegate option may also be an element on which to listen
        this.handle = Ext.get(this.delegate);

        // If delegate specified an actual element to listen on, we do not use the delegate listener option
        this.delegate = this.handle ? undefined : this.delegate;

        if (!this.handle) {
            this.handle = this.el;
        }

        // Add a mousedown listener which reacts only on the elements targeted by the delegate config.
        // We process mousedown to begin tracking.
        this.mon(this.handle, {
            mousedown: this.onMouseDown,
            delegate: this.delegate,
            scope: this
        });

        // If configured to do so, track mouse entry and exit into the target (or delegate).
        // The mouseover and mouseout CANNOT be replaced with mouseenter and mouseleave
        // because delegate cannot work with those pseudoevents. Entry/exit checking is done in the handler.
        if (this.trackOver || this.overCls) {
            this.mon(this.handle, {
                mouseover: this.onMouseOver,
                mouseout: this.onMouseOut,
                delegate: this.delegate,
                scope: this
            });
        }
    },

    disable: function() {
        this.disabled = true;
    },

    enable: function() {
        this.disabled = false;
    },

    destroy : function() {
        this.clearListeners();
        delete this.el;
    },

    // When the pointer enters a tracking element, fire a mouseover if the mouse entered from outside.
    // This is mouseenter functionality, but we cannot use mouseenter because we are using "delegate" to filter mouse targets
    onMouseOver: function(e, target) {
        var me = this;
        if (!me.disabled) {
            if (Ext.EventManager.contains(e) || me.delegate) {
                me.mouseIsOut = false;
                if (me.overCls) {
                    me.el.addCls(me.overCls);
                }
                me.fireEvent('mouseover', me, e, me.delegate ? e.getTarget(me.delegate, target) : me.handle);
            }
        }
    },

    // When the pointer exits a tracking element, fire a mouseout.
    // This is mouseleave functionality, but we cannot use mouseleave because we are using "delegate" to filter mouse targets
    onMouseOut: function(e) {
        if (this.mouseIsDown) {
            this.mouseIsOut = true;
        } else {
            if (this.overCls) {
                this.el.removeCls(this.overCls);
            }
            this.fireEvent('mouseout', this, e);
        }
    },

    onMouseDown: function(e, target){
        // If this is disabled, or the mousedown has been processed by an upstream DragTracker, return
        if (this.disabled ||e.dragTracked) {
            return;
        }

        // This information should be available in mousedown listener and onBeforeStart implementations
        this.dragTarget = this.delegate ? target : this.handle.dom;
        this.startXY = this.lastXY = e.getXY();
        this.startRegion = Ext.fly(this.dragTarget).getRegion();

        if (this.fireEvent('mousedown', this, e) === false ||
            this.fireEvent('beforedragstart', this, e) === false ||
            this.onBeforeStart(e) === false) {
            return;
        }

        // Track when the mouse is down so that mouseouts while the mouse is down are not processed.
        // The onMouseOut method will only ever be called after mouseup.
        this.mouseIsDown = true;

        // Flag for downstream DragTracker instances that the mouse is being tracked.
        e.dragTracked = true;

        if (this.preventDefault !== false) {
            e.preventDefault();
        }
        Ext.getDoc().on({
            scope: this,
            mouseup: this.onMouseUp,
            mousemove: this.onMouseMove,
            selectstart: this.stopSelect
        });
        if (this.autoStart) {
            this.timer =  Ext.defer(this.triggerStart, this.autoStart === true ? 1000 : this.autoStart, this, [e]);
        }
    },

    onMouseMove: function(e, target){
        // BrowserBug: IE hack to see if button was released outside of window.
        // Needed in IE6-9 in quirks and strictmode
        if (this.active && Ext.isIE && !e.browserEvent.button) {
            e.preventDefault();
            this.onMouseUp(e);
            return;
        }

        e.preventDefault();
        var xy = e.getXY(),
            s = this.startXY;

        this.lastXY = xy;
        if (!this.active) {
            if (Math.max(Math.abs(s[0]-xy[0]), Math.abs(s[1]-xy[1])) > this.tolerance) {
                this.triggerStart(e);
            } else {
                return;
            }
        }

        // Returning false from a mousemove listener deactivates
        if (this.fireEvent('mousemove', this, e) === false) {
            this.onMouseUp(e);
        } else {
            this.onDrag(e);
            this.fireEvent('drag', this, e);
        }
    },

    onMouseUp: function(e) {
        // Clear the flag which ensures onMouseOut fires only after the mouse button
        // is lifted if the mouseout happens *during* a drag.
        this.mouseIsDown = false;

        // If we mouseouted the el *during* the drag, the onMouseOut method will not have fired. Ensure that it gets processed.
        if (this.mouseIsOut) {
            this.mouseIsOut = false;
            this.onMouseOut(e);
        }
        e.preventDefault();
        this.fireEvent('mouseup', this, e);
        this.endDrag(e);
    },

    /**
     * @private
     * Stop the drag operation, and remove active mouse listeners.
     */
    endDrag: function(e) {
        var doc = Ext.getDoc(),
        wasActive = this.active;

        doc.un('mousemove', this.onMouseMove, this);
        doc.un('mouseup', this.onMouseUp, this);
        doc.un('selectstart', this.stopSelect, this);
        this.clearStart();
        this.active = false;
        if (wasActive) {
            this.onEnd(e);
            this.fireEvent('dragend', this, e);
        }
        // Private property calculated when first required and only cached during a drag
        delete this._constrainRegion;

        // Remove flag from event singleton.  Using "Ext.EventObject" here since "endDrag" is called directly in some cases without an "e" param
        delete Ext.EventObject.dragTracked;
    },

    triggerStart: function(e) {
        this.clearStart();
        this.active = true;
        this.onStart(e);
        this.fireEvent('dragstart', this, e);
    },

    clearStart : function() {
        if (this.timer) {
            clearTimeout(this.timer);
            delete this.timer;
        }
    },

    stopSelect : function(e) {
        e.stopEvent();
        return false;
    },

    /**
     * Template method which should be overridden by each DragTracker instance. Called when the user first clicks and
     * holds the mouse button down. Return false to disallow the drag
     * @param {Ext.EventObject} e The event object
     * @template
     */
    onBeforeStart : function(e) {

    },

    /**
     * Template method which should be overridden by each DragTracker instance. Called when a drag operation starts
     * (e.g. the user has moved the tracked element beyond the specified tolerance)
     * @param {Ext.EventObject} e The event object
     * @template
     */
    onStart : function(xy) {

    },

    /**
     * Template method which should be overridden by each DragTracker instance. Called whenever a drag has been detected.
     * @param {Ext.EventObject} e The event object
     * @template
     */
    onDrag : function(e) {

    },

    /**
     * Template method which should be overridden by each DragTracker instance. Called when a drag operation has been completed
     * (e.g. the user clicked and held the mouse down, dragged the element and then released the mouse button)
     * @param {Ext.EventObject} e The event object
     * @template
     */
    onEnd : function(e) {

    },

    /**
     * Returns the drag target. This is usually the DragTracker's encapsulating element.
     *
     * If the {@link #delegate} option is being used, this may be a child element which matches the
     * {@link #delegate} selector.
     *
     * @return {Ext.Element} The element currently being tracked.
     */
    getDragTarget : function(){
        return this.dragTarget;
    },

    /**
     * @private
     * @returns {Ext.Element} The DragTracker's encapsulating element.
     */
    getDragCt : function(){
        return this.el;
    },

    /**
     * @private
     * Return the Region into which the drag operation is constrained.
     * Either the XY pointer itself can be constrained, or the dragTarget element
     * The private property _constrainRegion is cached until onMouseUp
     */
    getConstrainRegion: function() {
        if (this.constrainTo) {
            if (this.constrainTo instanceof Ext.util.Region) {
                return this.constrainTo;
            }
            if (!this._constrainRegion) {
                this._constrainRegion = Ext.fly(this.constrainTo).getViewRegion();
            }
        } else {
            if (!this._constrainRegion) {
                this._constrainRegion = this.getDragCt().getViewRegion();
            }
        }
        return this._constrainRegion;
    },

    getXY : function(constrain){
        return constrain ? this.constrainModes[constrain](this, this.lastXY) : this.lastXY;
    },

    /**
     * Returns the X, Y offset of the current mouse position from the mousedown point.
     *
     * This method may optionally constrain the real offset values, and returns a point coerced in one
     * of two modes:
     *
     *  - `point`
     *    The current mouse position is coerced into the constrainRegion and the resulting position is returned.
     *  - `dragTarget`
     *    The new {@link Ext.util.Region Region} of the {@link #getDragTarget dragTarget} is calculated
     *    based upon the current mouse position, and then coerced into the constrainRegion. The returned
     *    mouse position is then adjusted by the same delta as was used to coerce the region.\
     *
     * @param constrainMode {String} (Optional) If omitted the true mouse position is returned. May be passed
     * as `point` or `dragTarget`. See above.
     * @returns {Number[]} The `X, Y` offset from the mousedown point, optionally constrained.
     */
    getOffset : function(constrain){
        var xy = this.getXY(constrain),
            s = this.startXY;

        return [xy[0]-s[0], xy[1]-s[1]];
    },

    constrainModes: {
        // Constrain the passed point to within the constrain region
        point: function(me, xy) {
            var dr = me.dragRegion,
                constrainTo = me.getConstrainRegion();

            // No constraint
            if (!constrainTo) {
                return xy;
            }

            dr.x = dr.left = dr[0] = dr.right = xy[0];
            dr.y = dr.top = dr[1] = dr.bottom = xy[1];
            dr.constrainTo(constrainTo);

            return [dr.left, dr.top];
        },

        // Constrain the dragTarget to within the constrain region. Return the passed xy adjusted by the same delta.
        dragTarget: function(me, xy) {
            var s = me.startXY,
                dr = me.startRegion.copy(),
                constrainTo = me.getConstrainRegion(),
                adjust;

            // No constraint
            if (!constrainTo) {
                return xy;
            }

            // See where the passed XY would put the dragTarget if translated by the unconstrained offset.
            // If it overflows, we constrain the passed XY to bring the potential
            // region back within the boundary.
            dr.translateBy(xy[0]-s[0], xy[1]-s[1]);

            // Constrain the X coordinate by however much the dragTarget overflows
            if (dr.right > constrainTo.right) {
                xy[0] += adjust = (constrainTo.right - dr.right);    // overflowed the right
                dr.left += adjust;
            }
            if (dr.left < constrainTo.left) {
                xy[0] += (constrainTo.left - dr.left);      // overflowed the left
            }

            // Constrain the Y coordinate by however much the dragTarget overflows
            if (dr.bottom > constrainTo.bottom) {
                xy[1] += adjust = (constrainTo.bottom - dr.bottom);  // overflowed the bottom
                dr.top += adjust;
            }
            if (dr.top < constrainTo.top) {
                xy[1] += (constrainTo.top - dr.top);        // overflowed the top
            }
            return xy;
        }
    }
});