source: Dev/trunk/src/client/dojo/back.js

define(["./_base/config", "./_base/lang", "./sniff", "./dom", "./dom-construct", "./_base/window", "require"],
        function(config, lang, has, dom, domConstruct, baseWindow, require){
        // module:
        //              dojo/back

        var back = {
                // summary:
                //              Browser history management resources
        };
        has("extend-dojo") && lang.setObject("dojo.back", back);

        // everyone deals with encoding the hash slightly differently

        var getHash = back.getHash = function(){
                var h = window.location.hash;
                if(h.charAt(0) == "#"){ h = h.substring(1); }
                return has("mozilla") ? h : decodeURIComponent(h);
        },

        setHash = back.setHash = function(h){
                if(!h){ h = ""; }
                window.location.hash = encodeURIComponent(h);
                historyCounter = history.length;
        };

        var initialHref = (typeof(window) !== "undefined") ? window.location.href : "";
        var initialHash = (typeof(window) !== "undefined") ? getHash() : "";
        var initialState = null;

        var locationTimer = null;
        var bookmarkAnchor = null;
        var historyIframe = null;
        var forwardStack = [];
        var historyStack = [];
        var moveForward = false;
        var changingUrl = false;
        var historyCounter;

        function handleBackButton(){
                // summary:
                //              private method. Do not call this directly.

                //The "current" page is always at the top of the history stack.
                var current = historyStack.pop();
                if(!current){ return; }
                var last = historyStack[historyStack.length-1];
                if(!last && historyStack.length == 0){
                        last = 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");
                        }
                }
                forwardStack.push(current);
        }

        back.goBack = handleBackButton;

        function handleForwardButton(){
                // summary:
                //              private method. Do not call this directly.
                var last = 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");
                }
                historyStack.push(last);
        }

        back.goForward = handleForwardButton;

        function createState(url, args, hash){
                // summary:
                //              private method. Do not call this directly.
                return {"url": url, "kwArgs": args, "urlHash": hash};   //Object
        }

        function getUrlQuery(url){
                // summary:
                //              private method. Do not call this directly.
                var segments = url.split("?");
                if(segments.length < 2){
                        return null; //null
                }
                else{
                        return segments[1]; //String
                }
        }

        function loadIframeHistory(){
                // summary:
                //              private method. Do not call this directly.
                var url = (config["dojoIframeHistoryUrl"] || require.toUrl("./resources/iframe_history.html")) + "?" + (new Date()).getTime();
                moveForward = true;
                if(historyIframe){
                        has("webkit") ? historyIframe.location = url : window.frames[historyIframe.name].location = url;
                }else{
                        //console.warn("dojo/back: Not initialised. You need to call back.init() from a <script> block that lives inside the <body> tag.");
                }
                return url; //String
        }

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

                        var hash = getHash();

                        if((hash === initialHash||window.location.href == 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);
                                handleBackButton();
                                return;
                        }

                        // first check to see if we could have gone forward. We always halt on
                        // a no-hash item.
                        if(forwardStack.length > 0){
                                if(forwardStack[forwardStack.length-1].urlHash === hash){
                                        handleForwardButton();
                                        return;
                                }
                        }

                        // ok, that didn't work, try someplace back in the history stack
                        if((hsl >= 2)&&(historyStack[hsl-2])){
                                if(historyStack[hsl-2].urlHash === hash){
                                        handleBackButton();
                                }
                        }
                }
        }

        back.init = function(){
                // summary:
                //              Initializes the undo stack. This must be called from a <script>
                //              block that lives inside the `<body>` tag to prevent bugs on IE.
                //
                //              Only call this method before the page's DOM is finished loading. Otherwise
                //              it will not work. Be careful with xdomain loading or djConfig.debugAtAllCosts scenarios,
                //              in order for this method to work, dojo/back will need to be part of a build layer.

                // prevent reinit
                if(dom.byId("dj_history")){ return; } 

                var src = config["dojoIframeHistoryUrl"] || require.toUrl("./resources/iframe_history.html");
                if (config.afterOnLoad){
                        console.error("dojo/back::init() must be called before the DOM has loaded. "
                                                + "Include dojo/back in a build layer.");
                }else{
                        document.write('<iframe style="border:0;width:1px;height:1px;position:absolute;visibility:hidden;bottom:0;right:0;" name="dj_history" id="dj_history" src="' + src + '"></iframe>');
                }
        };

        back.setInitialState = function(/*Object*/args){
                // summary:
                //              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/ready.
                // args: Object
                //              See the addToHistory() function for the list of valid args properties.
                initialState = createState(initialHref, args, initialHash);
        };

        //FIXME: Make these doc comments not be awful. At least they're not wrong.
        //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.


        /*=====
        var __backArgs = {
                // back: Function?
                //              A function to be called when this state is reached via the user
                //              clicking the back button.
                // forward: Function?
                //              Upon return to this state from the "back, forward" combination
                //              of navigation steps, this function will be called. Somewhat
                //              analogous to the semantic of an "onRedo" event handler.
                // changeUrl: Boolean|String?
                //              Boolean indicating whether or not to create a unique hash for
                //              this state. If a string is passed instead, it is used as the
                //              hash.
        };
        =====*/

        back.addToHistory = function(args){
                // summary:
                //              adds a state object (args) to the history list.
                // args: __backArgs
                //              The state object that will be added to the history list.
                // description:
                //              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
                //
                //              There are problems with using dojo/back with semantically-named fragment identifiers
                //              ("hash values" on an URL). In most browsers it will be hard for dojo/back to know
                //              distinguish a back from a forward event in those cases. For back/forward support to
                //              work best, the fragment ID should always be a unique value (something using new Date().getTime()
                //              for example). If you want to detect hash changes using semantic fragment IDs, then
                //              consider using dojo/hash instead (in Dojo 1.4+).
                //
                // example:
                //              |       back.addToHistory({
                //              |               back: function(){ console.log('back pressed'); },
                //              |               forward: function(){ console.log('forward pressed'); },
                //              |               changeUrl: true
                //              |       });

                //      BROWSER 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.

                //If addToHistory is called, then that means we prune the
                //forward stack -- the user went back, then wanted to
                //start a new forward path.
                forwardStack = [];

                var hash = null;
                var url = null;
                if(!historyIframe){
                        if(config["useXDomain"] && !config["dojoIframeHistoryUrl"]){
                                console.warn("dojo/back: When using cross-domain Dojo builds,"
                                        + " please save iframe_history.html to your domain and set djConfig.dojoIframeHistoryUrl"
                                        + " to the path on your domain to iframe_history.html");
                        }
                        historyIframe = window.frames["dj_history"];
                }
                if(!bookmarkAnchor){
                        bookmarkAnchor = domConstruct.create("a", {style: {display: "none"}}, baseWindow.body());
                }
                if(args["changeUrl"]){
                        hash = ""+ ((args["changeUrl"]!==true) ? args["changeUrl"] : (new Date()).getTime());

                        //If the current hash matches the new one, just replace the history object with
                        //this new one. It doesn't make sense to track different state objects for the same
                        //logical URL. This matches the browser behavior of only putting in one history
                        //item no matter how many times you click on the same #hash link, at least in Firefox
                        //and Safari, and there is no reliable way in those browsers to know if a #hash link
                        //has been clicked on multiple times. So making this the standard behavior in all browsers
                        //so that dojo/back's behavior is the same in all browsers.
                        if(historyStack.length == 0 && initialState.urlHash == hash){
                                initialState = createState(url, args, hash);
                                return;
                        }else if(historyStack.length > 0 && historyStack[historyStack.length - 1].urlHash == hash){
                                historyStack[historyStack.length - 1] = createState(url, args, hash);
                                return;
                        }

                        changingUrl = true;
                        setTimeout(function(){
                                        setHash(hash);
                                        changingUrl = false;
                                }, 1);
                        bookmarkAnchor.href = hash;

                        if(has("ie")){
                                url = loadIframeHistory();

                                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(getHash() != ""){
                                                setTimeout(function(){ setHash(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;
                                }

                                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(getHash() != ""){
                                                setHash(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(!has("ie")){
                                // start the timer
                                if(!locationTimer){
                                        locationTimer = setInterval(checkLocation, 200);
                                }

                        }
                }else{
                        url = loadIframeHistory();
                }

                historyStack.push(createState(url, args, hash));
        };

        back._iframeLoaded = function(evt, ifrLoc){
                // summary:
                //              private method. Do not call this directly.
                var query = getUrlQuery(ifrLoc.href);
                if(query == null){
                        // alert("iframeLoaded");
                        // we hit the end of the history, so we should go back
                        if(historyStack.length == 1){
                                handleBackButton();
                        }
                        return;
                }
                if(moveForward){
                        // we were expecting it, so it's not either a forward or backward movement
                        moveForward = false;
                        return;
                }

                //Check the back stack first, since it is more likely.
                //Note that only one step back or forward is supported.
                if(historyStack.length >= 2 && query == getUrlQuery(historyStack[historyStack.length-2].url)){
                        handleBackButton();
                }else if(forwardStack.length > 0 && query == getUrlQuery(forwardStack[forwardStack.length-1].url)){
                        handleForwardButton();
                }
        };

        return back;
        
});