Yahoo! UI Library

/**
 * A DragDrop implementation where the linked element follows the 
 * mouse cursor during a drag.
 * @class DD
 * @extends YAHOO.util.DragDrop
 * @constructor
 * @param {String} id the id of the linked element 
 * @param {String} sGroup the group of related DragDrop items
 * @param {object} config an object containing configurable attributes
 *                Valid properties for DD: 
 *                    scroll
 */
YAHOO.util.DD = function(id, sGroup, config) {
    if (id) {
        this.init(id, sGroup, config);
    }
};

YAHOO.extend(YAHOO.util.DD, YAHOO.util.DragDrop, {

    /**
     * When set to true, the utility automatically tries to scroll the browser
     * window wehn a drag and drop element is dragged near the viewport boundary.
     * Defaults to true.
     * @property scroll
     * @type boolean
     */
    scroll: true, 

    /**
     * Sets the pointer offset to the distance between the linked element's top 
     * left corner and the location the element was clicked
     * @method autoOffset
     * @param {int} iPageX the X coordinate of the click
     * @param {int} iPageY the Y coordinate of the click
     */
    autoOffset: function(iPageX, iPageY) {
        var x = iPageX - this.startPageX;
        var y = iPageY - this.startPageY;
        this.setDelta(x, y);
        // this.logger.log("autoOffset el pos: " + aCoord + ", delta: " + x + "," + y);
    },

    /** 
     * Sets the pointer offset.  You can call this directly to force the 
     * offset to be in a particular location (e.g., pass in 0,0 to set it 
     * to the center of the object, as done in YAHOO.widget.Slider)
     * @method setDelta
     * @param {int} iDeltaX the distance from the left
     * @param {int} iDeltaY the distance from the top
     */
    setDelta: function(iDeltaX, iDeltaY) {
        this.deltaX = iDeltaX;
        this.deltaY = iDeltaY;
        this.logger.log("deltaX:" + this.deltaX + ", deltaY:" + this.deltaY);
    },

    /**
     * Sets the drag element to the location of the mousedown or click event, 
     * maintaining the cursor location relative to the location on the element 
     * that was clicked.  Override this if you want to place the element in a 
     * location other than where the cursor is.
     * @method setDragElPos
     * @param {int} iPageX the X coordinate of the mousedown or drag event
     * @param {int} iPageY the Y coordinate of the mousedown or drag event
     */
    setDragElPos: function(iPageX, iPageY) {
        // the first time we do this, we are going to check to make sure
        // the element has css positioning

        var el = this.getDragEl();
        this.alignElWithMouse(el, iPageX, iPageY);
    },

    /**
     * Sets the element to the location of the mousedown or click event, 
     * maintaining the cursor location relative to the location on the element 
     * that was clicked.  Override this if you want to place the element in a 
     * location other than where the cursor is.
     * @method alignElWithMouse
     * @param {HTMLElement} el the element to move
     * @param {int} iPageX the X coordinate of the mousedown or drag event
     * @param {int} iPageY the Y coordinate of the mousedown or drag event
     */
    alignElWithMouse: function(el, iPageX, iPageY) {
        var oCoord = this.getTargetCoord(iPageX, iPageY);
        // this.logger.log("****alignElWithMouse : " + el.id + ", " + aCoord + ", " + el.style.display);

        if (!this.deltaSetXY) {
            var aCoord = [oCoord.x, oCoord.y];
            YAHOO.util.Dom.setXY(el, aCoord);
            var newLeft = parseInt( YAHOO.util.Dom.getStyle(el, "left"), 10 );
            var newTop  = parseInt( YAHOO.util.Dom.getStyle(el, "top" ), 10 );

            this.deltaSetXY = [ newLeft - oCoord.x, newTop - oCoord.y ];
        } else {
            YAHOO.util.Dom.setStyle(el, "left", (oCoord.x + this.deltaSetXY[0]) + "px");
            YAHOO.util.Dom.setStyle(el, "top",  (oCoord.y + this.deltaSetXY[1]) + "px");
        }
        
        this.cachePosition(oCoord.x, oCoord.y);
        this.autoScroll(oCoord.x, oCoord.y, el.offsetHeight, el.offsetWidth);
    },

    /**
     * Saves the most recent position so that we can reset the constraints and
     * tick marks on-demand.  We need to know this so that we can calculate the
     * number of pixels the element is offset from its original position.
     * @method cachePosition
     * @param iPageX the current x position (optional, this just makes it so we
     * don't have to look it up again)
     * @param iPageY the current y position (optional, this just makes it so we
     * don't have to look it up again)
     */
    cachePosition: function(iPageX, iPageY) {
        if (iPageX) {
            this.lastPageX = iPageX;
            this.lastPageY = iPageY;
        } else {
            var aCoord = YAHOO.util.Dom.getXY(this.getEl());
            this.lastPageX = aCoord[0];
            this.lastPageY = aCoord[1];
        }
    },

    /**
     * Auto-scroll the window if the dragged object has been moved beyond the 
     * visible window boundary.
     * @method autoScroll
     * @param {int} x the drag element's x position
     * @param {int} y the drag element's y position
     * @param {int} h the height of the drag element
     * @param {int} w the width of the drag element
     * @private
     */
    autoScroll: function(x, y, h, w) {

        if (this.scroll) {
            // The client height
            var clientH = this.DDM.getClientHeight();

            // The client width
            var clientW = this.DDM.getClientWidth();

            // The amt scrolled down
            var st = this.DDM.getScrollTop();

            // The amt scrolled right
            var sl = this.DDM.getScrollLeft();

            // Location of the bottom of the element
            var bot = h + y;

            // Location of the right of the element
            var right = w + x;

            // The distance from the cursor to the bottom of the visible area, 
            // adjusted so that we don't scroll if the cursor is beyond the
            // element drag constraints
            var toBot = (clientH + st - y - this.deltaY);

            // The distance from the cursor to the right of the visible area
            var toRight = (clientW + sl - x - this.deltaX);

            // this.logger.log( " x: " + x + " y: " + y + " h: " + h + 
            // " clientH: " + clientH + " clientW: " + clientW + 
            // " st: " + st + " sl: " + sl + " bot: " + bot + 
            // " right: " + right + " toBot: " + toBot + " toRight: " + toRight);

            // How close to the edge the cursor must be before we scroll
            // var thresh = (document.all) ? 100 : 40;
            var thresh = 40;

            // How many pixels to scroll per autoscroll op.  This helps to reduce 
            // clunky scrolling. IE is more sensitive about this ... it needs this 
            // value to be higher.
            var scrAmt = (document.all) ? 80 : 30;

            // Scroll down if we are near the bottom of the visible page and the 
            // obj extends below the crease
            if ( bot > clientH && toBot < thresh ) { 
                window.scrollTo(sl, st + scrAmt); 
            }

            // Scroll up if the window is scrolled down and the top of the object
            // goes above the top border
            if ( y < st && st > 0 && y - st < thresh ) { 
                window.scrollTo(sl, st - scrAmt); 
            }

            // Scroll right if the obj is beyond the right border and the cursor is
            // near the border.
            if ( right > clientW && toRight < thresh ) { 
                window.scrollTo(sl + scrAmt, st); 
            }

            // Scroll left if the window has been scrolled to the right and the obj
            // extends past the left border
            if ( x < sl && sl > 0 && x - sl < thresh ) { 
                window.scrollTo(sl - scrAmt, st);
            }
        }
    },

    /**
     * Finds the location the element should be placed if we want to move
     * it to where the mouse location less the click offset would place us.
     * @method getTargetCoord
     * @param {int} iPageX the X coordinate of the click
     * @param {int} iPageY the Y coordinate of the click
     * @return an object that contains the coordinates (Object.x and Object.y)
     * @private
     */
    getTargetCoord: function(iPageX, iPageY) {

        // this.logger.log("getTargetCoord: " + iPageX + ", " + iPageY);

        var x = iPageX - this.deltaX;
        var y = iPageY - this.deltaY;

        if (this.constrainX) {
            if (x < this.minX) { x = this.minX; }
            if (x > this.maxX) { x = this.maxX; }
        }

        if (this.constrainY) {
            if (y < this.minY) { y = this.minY; }
            if (y > this.maxY) { y = this.maxY; }
        }

        x = this.getTick(x, this.xTicks);
        y = this.getTick(y, this.yTicks);

        // this.logger.log("getTargetCoord " + 
                // " iPageX: " + iPageX +
                // " iPageY: " + iPageY +
                // " x: " + x + ", y: " + y);

        return {x:x, y:y};
    },

    /*
     * Sets up config options specific to this class. Overrides
     * YAHOO.util.DragDrop, but all versions of this method through the 
     * inheritance chain are called
     */
    applyConfig: function() {
        YAHOO.util.DD.superclass.applyConfig.call(this);
        this.scroll = (this.config.scroll !== false);
    },

    /*
     * Event that fires prior to the onMouseDown event.  Overrides 
     * YAHOO.util.DragDrop.
     */
    b4MouseDown: function(e) {
        // this.resetConstraints();
        this.autoOffset(YAHOO.util.Event.getPageX(e), 
                            YAHOO.util.Event.getPageY(e));
    },

    /*
     * Event that fires prior to the onDrag event.  Overrides 
     * YAHOO.util.DragDrop.
     */
    b4Drag: function(e) {
        this.setDragElPos(YAHOO.util.Event.getPageX(e), 
                            YAHOO.util.Event.getPageY(e));
    },

    toString: function() {
        return ("DD " + this.id);
    }

    //////////////////////////////////////////////////////////////////////////
    // Debugging ygDragDrop events that can be overridden
    //////////////////////////////////////////////////////////////////////////
    /*
    startDrag: function(x, y) {
        this.logger.log(this.id.toString()  + " startDrag");
    },

    onDrag: function(e) {
        this.logger.log(this.id.toString() + " onDrag");
    },

    onDragEnter: function(e, id) {
        this.logger.log(this.id.toString() + " onDragEnter: " + id);
    },

    onDragOver: function(e, id) {
        this.logger.log(this.id.toString() + " onDragOver: " + id);
    },

    onDragOut: function(e, id) {
        this.logger.log(this.id.toString() + " onDragOut: " + id);
    },

    onDragDrop: function(e, id) {
        this.logger.log(this.id.toString() + " onDragDrop: " + id);
    },

    endDrag: function(e) {
        this.logger.log(this.id.toString() + " endDrag");
    }

    */

});