var kShadowPadding = 17;

var kDefaultMagnifierSize = 2; // index into the arrays below

var kMagnifierSizes = new Array(0, 100, 150, 300);
var kMagnifierSizeNames = new Array('off', 'small', 'medium', 'large');

var kControllerPrefix = 'Magnifier  ';


function MagnifierPosition()
{			
	this.style.left = Math.round(this.xPosition - 1 - this.size/2) + "px"; // -1 to account for the border
this.style.top = Math.round(this.yPosition - 1 - this.size/2) + "px";

this.shadow.style.left = Math.round(this.xPosition - this.size/2 - kShadowPadding) + "px";
this.shadow.style.top = Math.round(this.yPosition - this.size/2 - kShadowPadding) + "px";

var magnifierCenterX = Math.round(this.xPosition * this.xMultiplier - this.size/2);
var	magnifierCenterY = Math.round(this.yPosition * this.yMultiplier - this.size/2);
	
this.style.backgroundPosition = -magnifierCenterX + "px " +
								-magnifierCenterY + "px";
}

function ControllerSizeButtonClick(event)
{
	if (!event) event = window.event;
	
	var button = event.currentTarget || event.srcElement;
	
	button.parentNode.magnifier.resize(button.magnifierSize);
}

function MagnifierResize(size)
{
	this.size = kMagnifierSizes[size];
	
	for (var i=0; i < this.controller.sizeButtons.length; i++)
	{
		if (i == size)
			this.controller.sizeButtons[i].className = "magnifierControllerButtonSelected";
	else
		this.controller.sizeButtons[i].className = "magnifierControllerButton";
}

if (this.size == 0)
{
	this.shadow.style.display = "none";
	this.style.display = "none";
}
else
{
	var shadow = this.shadow;
	var shadowSize = this.size + 2 * kShadowPadding;
	
	// MSIE 5.x/6.x must be treated specially in order to make them use the PNG alpha channel
	var shadowImageSrc = "assets/shadow" + size + ".png";
	if (shadow.runtimeStyle)
		shadow.runtimeStyle.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='" +
								     shadowImageSrc +
									 "', sizingMethod='scale')";
	else
		shadow.style.backgroundImage = "url(" + shadowImageSrc + ")";
	shadow.style.width = shadowSize + "px";
	shadow.style.height = shadowSize + "px";
	shadow.style.display = "block";
	
	if (this.runtimeStyle) // msie counts the border as being part of the width
		this.size += 2; // must compensate
	
	this.style.width = this.size + "px";
	this.style.height = this.size + "px";
	this.style.display = "block";
		this.position();
	}
}

function MagnifierMouseDown(event)
{
	if (!event) event = window.event;
	
	document.body.magnifier = this;
	this.inDrag = true;
	if (event.pageX)
	{
		this.startX = event.pageX;
		this.startY = event.pageY;
	}
	else if (event.clientX)
	{
		this.startX = event.clientX;
		this.startY = event.clientY;
	}
	else
	{
		alert("don't know how to get position out of event");
	return;
}
this.savedCursor = this.style.cursor;
this.style.cursor = "grab";
}

function MagnifierMouseUp()
{
	if (this.inDrag)
	{
		this.inDrag = false;
		this.style.cursor = this.savedCursor;
		document.body.magnifier = null;
	}
}

function MagnifierDrag(event)
{
	if (!event) event = window.event;
	var magnifier = this.magnifier; // we're actually in the body's onmousemove handler
	
	if (magnifier && magnifier.inDrag)
	{
		var eventX;
		var eventY;
		
		if (event.pageX)
		{
			eventX = event.pageX;
			eventY = event.pageY;
		}
		else if (event.clientX)
		{
			eventX = event.clientX;
			eventY = event.clientY;
		}
		else
		{
			return;
		}
		
		magnifier.xPosition += eventX - magnifier.startX;
		magnifier.yPosition += eventY - magnifier.startY;
		
		magnifier.startX = eventX;
		magnifier.startY = eventY;
		
		magnifier.position();
	}
}

function loadMagnifier(baseID, zoomedURL, zoomedWidth, zoomedHeight)
{
	this.document = document;
	// get the zoomed image (load as early as possible)
var zoomedImage = document.createElement("img");
zoomedImage.src = zoomedURL;

// get the div's
var base = document.getElementById(baseID);
var magnifier = document.createElement("div");

// get the regular image
var normalImage = null;
for (var i=0; i < base.childNodes.length; i++)
{
	if (base.childNodes[i].tagName &&
		base.childNodes[i].tagName.toLowerCase() == "img")
	{
		normalImage = base.childNodes[i];
		break;
	}
}

if (normalImage == null)
{
	alert("couldn't find normal image for magnifier " + baseID);
	return;
}

magnifier.xMultiplier = zoomedWidth/normalImage.width;
magnifier.yMultiplier = zoomedHeight/normalImage.height;

magnifier.size = kMagnifierSizes[kDefaultMagnifierSize];
magnifier.xPosition = normalImage.width - magnifier.size/2 - 20;
magnifier.yPosition = normalImage.height - magnifier.size/2 + 30;

magnifier.id = baseID + "Magnifier";
magnifier.className = "magnifier";

// styles (only dynamic ones, rest are part of the class)
magnifier.style.backgroundImage = "url(" + zoomedURL + ")";

// functions
magnifier.onmousedown = MagnifierMouseDown;
magnifier.onmouseup = MagnifierMouseUp;
document.body.onmousemove = MagnifierDrag; // we attach this handler to the body because if the user moves
										   // the mouse fast enough, it'll go outside the boundaries of the
										   // magnifier, and then the magnifier's mousemove handler won't fire

magnifier.position = MagnifierPosition;
magnifier.resize = MagnifierResize;

// controller
var controller = document.createElement("span");

controller.id = baseID + "MagnifierController";
controller.className = "magnifierController";

var controllerPrefix = document.createElement("span");
controllerPrefix.innerHTML = kControllerPrefix;

controllerPrefix.className = "magnifierControllerPrefix";
controller.appendChild(controllerPrefix);

controller.sizeButtons = new Array(kMagnifierSizes.length);



for (var i=0; i < kMagnifierSizes.length; i++)
{
	var button = document.createElement("span");
	button.innerHTML = kMagnifierSizeNames[i];
	button.className = "magnifierControllerButton";
	button.onclick = ControllerSizeButtonClick;
	button.magnifierSize = i;
	
	controller.sizeButtons[i] = button;
	controller.appendChild(button);
}

// shadow
var shadow = document.createElement("div");

shadow.id = baseID + "MagnifierShadow";
shadow.className = "magnifierShadow";

// point objects at each other
magnifier.controller = controller;
controller.magnifier = magnifier;
magnifier.shadow = shadow;

// add to document and lay out

var controllerContainer = document.createElement("div");

controllerContainer.className = "magnifierControllerContainer";

controllerContainer.appendChild(controller);

base.insertBefore(controllerContainer, document.getElementById("message"));
base.appendChild(shadow);
base.appendChild(magnifier);
magnifier.resize(kDefaultMagnifierSize); // also positions
}