var Drag = {
  // The current element being dragged
  obj: null,
  // The initalization function for the drag object
  // o = The element to act as the drag handle
  // oRoot = The element to be dragged, if not specified, the handle will be the element dragged.
  // minX, maxX, minY, maxY = The min and max coordinates allowed for the element
  // bSwapHorzRef = Toggle the horizontal coordinate system
  // bSwapVertRef = Toggle the vertical coordinate system
  // fxMapper, fyMapper =  Functions for mapping x and y coordinates to others
  init: function(o, oRoot, minX, maxX, minY, maxY, bSwapHorzRef, bSwapVertRef, fXMapper, fYMapper) {
    // Watch for the drag event to start
    o.onmousedown = Drag.start;
    // Figure out which coordinate system is being used
    o.hmode = bSwapHorzRef ? false : true ;
    o.vmode = bSwapVertRef ? false : true ;
    // Figure out which element is acting as the draggable 'handle'
    o.root = oRoot && oRoot != null ? oRoot : o ;
    // Initalize the specified coordinate system
    if (o.hmode && isNaN(parseInt(o.root.style.left ))) o.root.style.left   = "0px";
    if (o.vmode && isNaN(parseInt(o.root.style.top ))) o.root.style.top    = "0px";
    if (!o.hmode && isNaN(parseInt(o.root.style.right ))) o.root.style.right  = "0px";
    if (!o.vmode && isNaN(parseInt(o.root.style.bottom))) o.root.style.bottom = "0px";
    // Look to see if the user provided min/max x/y coordinates
    o.minX = typeof minX != 'undefined' ? minX : null;
    o.minY = typeof minY != 'undefined' ? minY : null;
    o.maxX = typeof maxX != 'undefined' ? maxX : null;
    o.maxY = typeof maxY != 'undefined' ? maxY : null;
    // Check for any specified x and y coordinate mappers
    o.xMapper = fXMapper ? fXMapper : null;
    o.yMapper = fYMapper ? fYMapper : null;
    // Add shells for all the user-defined functions
    o.root.onDragStart = new Function();
    o.root.onDragEnd  = new Function();
    o.root.onDrag = new Function();
  },
  start: function(e) {
    // Figure out the object that's being dragged
    var o = Drag.obj = this;
    // Normalize the event object
    e = Drag.fixE(e);
    // Get the current x and y coordinates
    var y = parseInt(o.vmode ? o.root.style.top  : o.root.style.bottom);
    var x = parseInt(o.hmode ? o.root.style.left : o.root.style.right );
    // Call the user's function with the current x and y coordinates
    o.root.onDragStart(x, y);
    // Remember the starting mouse position
    o.lastMouseX = e.clientX;
    o.lastMouseY = e.clientY;
    // If we're using the CSS coordinate system
    if (o.hmode) {
        // set the min and max coordiantes, where applicable
        if (o.minX != null) o.minMouseX    = e.clientX - x + o.minX;
        if (o.maxX != null) o.maxMouseX    = o.minMouseX + o.maxX - o.minX;
    // Otherwise, we're using a traditional mathematical coordinate system
    } else {
        if (o.minX != null) o.maxMouseX = -o.minX + e.clientX + x;
        if (o.maxX != null) o.minMouseX = -o.maxX + e.clientX + x;
    }
    // If we're using the CSS coordinate system
    if (o.vmode) {
        // set the min and max coordiantes, where applicable
        if (o.minY != null) o.minMouseY    = e.clientY - y + o.minY;
        if (o.maxY != null) o.maxMouseY    = o.minMouseY + o.maxY - o.minY;
    // Otherwise, we're using a traditional mathematical coordinate system
    } else {
        if (o.minY != null) o.maxMouseY = -o.minY + e.clientY + y;
        if (o.maxY != null) o.minMouseY = -o.maxY + e.clientY + y;
    }
    // Watch for 'dragging' and 'drag end' events
    document.onmousemove = Drag.drag;
    document.onmouseup = Drag.end;
    return false;
  },
  // A function to watch for all movements of the mouse during the drag event
  drag: function(e) {
      // Normalize the event object
      e = Drag.fixE(e);
      // Get our reference to the element being dragged
      var o = Drag.obj;
      // Get the position of the mouse within the window
      var ey = e.clientY;
      var ex = e.clientX;
      // Get the current x and y coordinates
      var y = parseInt(o.vmode ? o.root.style.top  : o.root.style.bottom);
      var x = parseInt(o.hmode ? o.root.style.left : o.root.style.right );
      var nx, ny;
      // If a minimum X position was set, make sure it doesn't go past that
      if (o.minX != null) ex = o.hmode ?
          Math.max(ex, o.minMouseX) : Math.min(ex, o.maxMouseX);
      // If a maximum X position was set, make sure it doesn't go past that
      if (o.maxX != null) ex = o.hmode ?
          Math.min(ex, o.maxMouseX) : Math.max(ex, o.minMouseX);
      // If a minimum Y position was set, make sure it doesn't go past that
      if (o.minY != null) ey = o.vmode ?
          Math.max(ey, o.minMouseY) : Math.min(ey, o.maxMouseY);
      // If a maximum Y position was set, make sure it doesn't go past that
      if (o.maxY != null) ey = o.vmode ?
          Math.min(ey, o.maxMouseY) : Math.max(ey, o.minMouseY);
      // Figure out the newly translated x and y coordinates
      nx = x + ((ex - o.lastMouseX) * (o.hmode ? 1 : -1));
      ny = y + ((ey - o.lastMouseY) * (o.vmode ? 1 : -1));
      // and translate them using an x or y mapper function (if provided)
      if (o.xMapper) nx = o.xMapper(y)
      else if (o.yMapper) ny = o.yMapper(x)
      // Set the new x and y coordinates onto the element
      Drag.obj.root.style[o.hmode ? "left" : "right"] = nx + "px";
      Drag.obj.root.style[o.vmode ? "top" : "bottom"] = ny + "px";
      // and remember  the last position of the mouse
      Drag.obj.lastMouseX = ex;
      Drag.obj.lastMouseY = ey;
      // Call the user's onDrag  function with the current x and y coordinates
      Drag.obj.root.onDrag(nx, ny);
      return false;
  },
  // Function that handles the end of a drag event
  end: function() {
      // No longer watch for mouse events (as the drag is done)
      document.onmousemove = null;
      document.onmouseup = null;
      // Call our special onDragEnd function with the x and y coordinates
      // of the element at the end of the drag event
      Drag.obj.root.onDragEnd(
          parseInt(Drag.obj.root.style[Drag.obj.hmode ? "left" : "right"]),
          parseInt(Drag.obj.root.style[Drag.obj.vmode ? "top" : "bottom"]));
      // No longer watch the object for drags
      Drag.obj = null;
  },
  // A function for normalizes the event object
  fixE: function(e) {
      // If no event object exists, then this is IE, so provide IE's event object
      if (typeof e == 'undefined') e = window.event;
      // If the layer properties aren't set, get the values from the equivalent
      // offset properties
      if (typeof e.layerX == 'undefined') e.layerX = e.offsetX;
      if (typeof e.layerY == 'undefined') e.layerY = e.offsetY;
      return e;
  }
};