/*
	Copyright (c) 2004-2006, The Dojo Foundation
	All Rights Reserved.

	Licensed under the Academic Free License version 2.1 or above OR the
	modified BSD license. For more information on Dojo licensing, see:

		http://dojotoolkit.org/community/licensing.shtml
*/

dojo.provide("dojo.undo.browser");
dojo.require("dojo.io");

try{
	if((!djConfig["preventBackButtonFix"])&&(!dojo.hostenv.post_load_)){
		document.write("<iframe style='border: 0px; width: 1px; height: 1px; position: absolute; bottom: 0px; right: 0px; visibility: visible;' name='djhistory' id='djhistory' src='"+(dojo.hostenv.getBaseScriptUri()+'iframe_history.html')+"'></iframe>");
	}
}catch(e){/* squelch */}

if(dojo.render.html.opera){
	dojo.debug("Opera is not supported with dojo.undo.browser, so back/forward detection will not work.");
}

/* NOTES:
 *  Safari 1.2: 
 *	back button "works" fine, however it's not possible to actually
 *	DETECT that you've moved backwards by inspecting window.location.
 *	Unless there is some other means of locating.
 *	FIXME: perhaps we can poll on history.length?
 *  Safari 2.0.3+ (and probably 1.3.2+):
 *	works fine, except when changeUrl is used. When changeUrl is used,
 *	Safari jumps all the way back to whatever page was shown before
 *	the page that uses dojo.undo.browser support.
 *  IE 5.5 SP2:
 *	back button behavior is macro. It does not move back to the
 *	previous hash value, but to the last full page load. This suggests
 *	that the iframe is the correct way to capture the back button in
 *	these cases.
 *	Don't test this page using local disk for MSIE. MSIE will not create 
 *	a history list for iframe_history.html if served from a file: URL. 
 *	The XML served back from the XHR tests will also not be properly 
 *	created if served from local disk. Serve the test pages from a web 
 *	server to test in that browser.
 *  IE 6.0:
 *	same behavior as IE 5.5 SP2
 * Firefox 1.0:
 *	the back button will return us to the previous hash on the same
 *	page, thereby not requiring an iframe hack, although we do then
 *	need to run a timer to detect inter-page movement.
 */
dojo.undo.browser = {
	initialHref: window.location.href,
	initialHash: window.location.hash,

	moveForward: false,
	historyStack: [],
	forwardStack: [],
	historyIframe: null,
	bookmarkAnchor: null,
	locationTimer: null,

	/**
	 * setInitialState sets the state object and back callback for the very first page that is loaded.
	 * It is recommended that you call this method as part of an event listener that is registered via
	 * dojo.addOnLoad().
	 */
	setInitialState: function(args){
		this.initialState = {"url": this.initialHref, "kwArgs": args, "urlHash": this.initialHash};
	},

	//FIXME: Would like to support arbitrary back/forward jumps. Have to rework iframeLoaded among other things.
	//FIXME: is there a slight race condition in moz using change URL with the timer check and when
	//       the hash gets set? I think I have seen a back/forward call in quick succession, but not consistent.
	/**
	 * addToHistory takes one argument, and it is an object that defines the following functions:
	 * - To support getting back button notifications, the object argument should implement a
	 *   function called either "back", "backButton", or "handle". The string "back" will be
	 *   passed as the first and only argument to this callback.
	 * - To support getting forward button notifications, the object argument should implement a
	 *   function called either "forward", "forwardButton", or "handle". The string "forward" will be
	 *   passed as the first and only argument to this callback.
	 * - If you want the browser location string to change, define "changeUrl" on the object. If the
	 *   value of "changeUrl" is true, then a unique number will be appended to the URL as a fragment
	 *   identifier (http://some.domain.com/path#uniquenumber). If it is any other value that does
	 *   not evaluate to false, that value will be used as the fragment identifier. For example,
	 *   if changeUrl: 'page1', then the URL will look like: http://some.domain.com/path#page1
	 *   
	 * Full example:
	 * 
	 * dojo.undo.browser.addToHistory({
	 *   back: function() { alert('back pressed'); },
	 *   forward: function() { alert('forward pressed'); },
	 *   changeUrl: true
	 * });
	 */
	addToHistory: function(args){
		var hash = null;
		if(!this.historyIframe){
			this.historyIframe = window.frames["djhistory"];
		}
		if(!this.bookmarkAnchor){
			this.bookmarkAnchor = document.createElement("a");
			(document.body||document.getElementsByTagName("body")[0]).appendChild(this.bookmarkAnchor);
			this.bookmarkAnchor.style.display = "none";
		}
		if((!args["changeUrl"])||(dojo.render.html.ie)){
			var url = dojo.hostenv.getBaseScriptUri()+"iframe_history.html?"+(new Date()).getTime();
			this.moveForward = true;
			dojo.io.setIFrameSrc(this.historyIframe, url, false);
		}
		if(args["changeUrl"]){
			this.changingUrl = true;
			hash = "#"+ ((args["changeUrl"]!==true) ? args["changeUrl"] : (new Date()).getTime());
			setTimeout("window.location.href = '"+hash+"'; dojo.undo.browser.changingUrl = false;", 1);
			this.bookmarkAnchor.href = hash;
			
			if(dojo.render.html.ie){
				var oldCB = args["back"]||args["backButton"]||args["handle"];

				//The function takes handleName as a parameter, in case the
				//callback we are overriding was "handle". In that case,
				//we will need to pass the handle name to handle.
				var tcb = function(handleName){
					if(window.location.hash != ""){
						setTimeout("window.location.href = '"+hash+"';", 1);
					}
					//Use apply to set "this" to args, and to try to avoid memory leaks.
					oldCB.apply(this, [handleName]);
				}
		
				//Set interceptor function in the right place.
				if(args["back"]){
					args.back = tcb;
				}else if(args["backButton"]){
					args.backButton = tcb;
				}else if(args["handle"]){
					args.handle = tcb;
				}
		
				//If addToHistory is called, then that means we prune the
				//forward stack -- the user went back, then wanted to
				//start a new forward path.
				this.forwardStack = []; 
				var oldFW = args["forward"]||args["forwardButton"]||args["handle"];
		
				//The function takes handleName as a parameter, in case the
				//callback we are overriding was "handle". In that case,
				//we will need to pass the handle name to handle.
				var tfw = function(handleName){
					if(window.location.hash != ""){
						window.location.href = hash;
					}
					if(oldFW){ // we might not actually have one
						//Use apply to set "this" to args, and to try to avoid memory leaks.
						oldFW.apply(this, [handleName]);
					}
				}

				//Set interceptor function in the right place.
				if(args["forward"]){
					args.forward = tfw;
				}else if(args["forwardButton"]){
					args.forwardButton = tfw;
				}else if(args["handle"]){
					args.handle = tfw;
				}

			}else if(dojo.render.html.moz){
				// start the timer
				if(!this.locationTimer){
					this.locationTimer = setInterval("dojo.undo.browser.checkLocation();", 200);
				}
			}
		}

		this.historyStack.push({"url": url, "kwArgs": args, "urlHash": hash});
	},

	checkLocation: function(){
		if (!this.changingUrl){
			var hsl = this.historyStack.length;

			if((window.location.hash == this.initialHash||window.location.href == this.initialHref)&&(hsl == 1)){
				// FIXME: could this ever be a forward button?
				// we can't clear it because we still need to check for forwards. Ugg.
				// clearInterval(this.locationTimer);
				this.handleBackButton();
				return;
			}
			// first check to see if we could have gone forward. We always halt on
			// a no-hash item.
			if(this.forwardStack.length > 0){
				if(this.forwardStack[this.forwardStack.length-1].urlHash == window.location.hash){
					this.handleForwardButton();
					return;
				}
			}
	
			// ok, that didn't work, try someplace back in the history stack
			if((hsl >= 2)&&(this.historyStack[hsl-2])){
				if(this.historyStack[hsl-2].urlHash==window.location.hash){
					this.handleBackButton();
					return;
				}
			}
		}
	},

	iframeLoaded: function(evt, ifrLoc){
		if(!dojo.render.html.opera){
			var query = this._getUrlQuery(ifrLoc.href);
			if(query == null){ 
				// alert("iframeLoaded");
				// we hit the end of the history, so we should go back
				if(this.historyStack.length == 1){
					this.handleBackButton();
				}
				return;
			}
			if(this.moveForward){
				// we were expecting it, so it's not either a forward or backward movement
				this.moveForward = false;
				return;
			}
	
			//Check the back stack first, since it is more likely.
			//Note that only one step back or forward is supported.
			if(this.historyStack.length >= 2 && query == this._getUrlQuery(this.historyStack[this.historyStack.length-2].url)){
				this.handleBackButton();
			}
			else if(this.forwardStack.length > 0 && query == this._getUrlQuery(this.forwardStack[this.forwardStack.length-1].url)){
				this.handleForwardButton();
			}
		}
	},

	handleBackButton: function(){
		//The "current" page is always at the top of the history stack.
		var current = this.historyStack.pop();
		if(!current){ return; }
		var last = this.historyStack[this.historyStack.length-1];
		if(!last && this.historyStack.length == 0){
			last = this.initialState;
		}
		if (last){
			if(last.kwArgs["back"]){
				last.kwArgs["back"]();
			}else if(last.kwArgs["backButton"]){
				last.kwArgs["backButton"]();
			}else if(last.kwArgs["handle"]){
				last.kwArgs.handle("back");
			}
		}
		this.forwardStack.push(current);
	},

	handleForwardButton: function(){
		var last = this.forwardStack.pop();
		if(!last){ return; }
		if(last.kwArgs["forward"]){
			last.kwArgs.forward();
		}else if(last.kwArgs["forwardButton"]){
			last.kwArgs.forwardButton();
		}else if(last.kwArgs["handle"]){
			last.kwArgs.handle("forward");
		}
		this.historyStack.push(last);
	},

	_getUrlQuery: function(url){
		var segments = url.split("?");
		if (segments.length < 2){
			return null;
		}
		else{
			return segments[1];
		}
	}
}