/**
 * @author Ed Spencer
 */
Ext.define('Ext.ux.DataView.DragSelector', {
    requires: ['Ext.dd.DragTracker', 'Ext.util.Region'],

    /**
     * Initializes the plugin by setting up the drag tracker
     */
    init: function(dataview) {
        /**
         * @property dataview
         * @type Ext.view.View
         * The DataView bound to this instance
         */
        this.dataview = dataview;
        dataview.mon(dataview, {
            beforecontainerclick: this.cancelClick,
            scope: this,
            render: {
                fn: this.onRender,
                scope: this,
                single: true
            }
        });
    },

    /**
     * @private
     * Called when the attached DataView is rendered. This sets up the DragTracker instance that will be used
     * to created a dragged selection area
     */
    onRender: function() {
        /**
         * @property tracker
         * @type Ext.dd.DragTracker
         * The DragTracker attached to this instance. Note that the 4 on* functions are called in the scope of the 
         * DragTracker ('this' refers to the DragTracker inside those functions), so we pass a reference to the 
         * DragSelector so that we can call this class's functions.
         */
        this.tracker = Ext.create('Ext.dd.DragTracker', {
            dataview: this.dataview,
            el: this.dataview.el,
            dragSelector: this,
            onBeforeStart: this.onBeforeStart,
            onStart: this.onStart,
            onDrag : this.onDrag,
            onEnd  : this.onEnd
        });

        /**
         * @property dragRegion
         * @type Ext.util.Region
         * Represents the region currently dragged out by the user. This is used to figure out which dataview nodes are
         * in the selected area and to set the size of the Proxy element used to highlight the current drag area
         */
        this.dragRegion = Ext.create('Ext.util.Region');
    },

    /**
     * @private
     * Listener attached to the DragTracker's onBeforeStart event. Returns false if the drag didn't start within the
     * DataView's el
     */
    onBeforeStart: function(e) {
        return e.target == this.dataview.getEl().dom;
    },

    /**
     * @private
     * Listener attached to the DragTracker's onStart event. Cancel's the DataView's containerclick event from firing
     * and sets the start co-ordinates of the Proxy element. Clears any existing DataView selection
     * @param {Ext.EventObject} e The click event
     */
    onStart: function(e) {
        var dragSelector = this.dragSelector,
            dataview     = this.dataview;

        // Flag which controls whether the cancelClick method vetoes the processing of the DataView's containerclick event.
        // On IE (where else), this needs to remain set for a millisecond after mouseup because even though the mouse has
        // moved, the mouseup will still trigger a click event.
        this.dragging = true;

        //here we reset and show the selection proxy element and cache the regions each item in the dataview take up
        dragSelector.fillRegions();
        dragSelector.getProxy().show();
        dataview.getSelectionModel().deselectAll();
    },

    /**
     * @private
     * Reusable handler that's used to cancel the container click event when dragging on the dataview. See onStart for
     * details
     */
    cancelClick: function() {
        return !this.tracker.dragging;
    },

    /**
     * @private
     * Listener attached to the DragTracker's onDrag event. Figures out how large the drag selection area should be and
     * updates the proxy element's size to match. Then iterates over all of the rendered items and marks them selected
     * if the drag region touches them
     * @param {Ext.EventObject} e The drag event
     */
    onDrag: function(e) {
        var dragSelector = this.dragSelector,
            selModel     = dragSelector.dataview.getSelectionModel(),
            dragRegion   = dragSelector.dragRegion,
            bodyRegion   = dragSelector.bodyRegion,
            proxy        = dragSelector.getProxy(),
            regions      = dragSelector.regions,
            length       = regions.length,

            startXY   = this.startXY,
            currentXY = this.getXY(),
            minX      = Math.min(startXY[0], currentXY[0]),
            minY      = Math.min(startXY[1], currentXY[1]),
            width     = Math.abs(startXY[0] - currentXY[0]),
            height    = Math.abs(startXY[1] - currentXY[1]),
            region, selected, i;

        Ext.apply(dragRegion, {
            top: minY,
            left: minX,
            right: minX + width,
            bottom: minY + height
        });

        dragRegion.constrainTo(bodyRegion);
        proxy.setRegion(dragRegion);

        for (i = 0; i < length; i++) {
            region = regions[i];
            selected = dragRegion.intersect(region);

            if (selected) {
                selModel.select(i, true);
            } else {
                selModel.deselect(i);
            }
        }
    },

    /**
     * @private
     * Listener attached to the DragTracker's onEnd event. This is a delayed function which executes 1
     * millisecond after it has been called. This is because the dragging flag must remain active to cancel
     * the containerclick event which the mouseup event will trigger.
     * @param {Ext.EventObject} e The event object
     */
    onEnd: Ext.Function.createDelayed(function(e) {
        var dataview = this.dataview,
            selModel = dataview.getSelectionModel(),
            dragSelector = this.dragSelector;

        this.dragging = false;
        dragSelector.getProxy().hide();
    }, 1),

    /**
     * @private
     * Creates a Proxy element that will be used to highlight the drag selection region
     * @return {Ext.Element} The Proxy element
     */
    getProxy: function() {
        if (!this.proxy) {
            this.proxy = this.dataview.getEl().createChild({
                tag: 'div',
                cls: 'x-view-selector'
            });
        }
        return this.proxy;
    },

    /**
     * @private
     * Gets the region taken up by each rendered node in the DataView. We use these regions to figure out which nodes
     * to select based on the selector region the user has dragged out
     */
    fillRegions: function() {
        var dataview = this.dataview,
            regions  = this.regions = [];

        dataview.all.each(function(node) {
            regions.push(node.getRegion());
        });
        this.bodyRegion = dataview.getEl().getRegion();
    }
});