Fix https://github.com/mozilla/thimble.webmaker.org/issues/956 - remember preview scroll position

src/extensions/default/bramble/lib/PostMessageTransport.js

@@ -21,6 +21,7 @@ define(function (require, exports, module) {
     // The script that will be injected into the previewed HTML to handle the other side of the post message connection.
     var PostMessageTransportRemote = require("text!lib/PostMessageTransportRemote.js");
     var Tutorial = require("lib/Tutorial");
+    var ScrollManager = require("lib/ScrollManager");
 
     // An XHR shim will be injected as well to allow XHR to the file system
     var XHRShim = require("text!lib/xhr/XHRShim.js");
@@ -164,9 +165,16 @@ define(function (require, exports, module) {
      * @return {string}
      */
     function getRemoteScript() {
+        var currentDoc = LiveDevMultiBrowser._getCurrentLiveDoc();
+        var currentPath;
+        if(currentDoc) {
+            currentPath = currentDoc.doc.file.fullPath;
+        }
+
         return '<base href="' + window.location.href + '">\n' +
             "<script>\n" + PostMessageTransportRemote + "</script>\n" +
-            "<script>\n" + XHRShim + "</script>\n";
+            "<script>\n" + XHRShim + "</script>\n" +
+            ScrollManager.getRemoteScript(currentPath);
     }
 
     // URL of document being rewritten/launched (if any)

src/extensions/default/bramble/lib/ScrollManager.js

@@ -0,0 +1,15 @@
+define(function (require, exports, module) {
+    "use strict";
+
+    var ScrollManagerRemote = require("text!lib/ScrollManagerRemote.js");
+
+    function getRemoteScript(filename) {
+        filename = filename || "unknown";
+
+        // Track scroll position per filename, so you can be at different points in each doc
+        return "<script>window.___brambleFilename = '" + filename + "';</script>\n" +
+               "<script>\n" + ScrollManagerRemote + "</script>\n";
+    }
+
+    exports.getRemoteScript = getRemoteScript;
+});

src/extensions/default/bramble/lib/ScrollManagerRemote.js

@@ -0,0 +1,17 @@
+/*jslint vars: true, plusplus: true, devel: true, nomen: true, indent: 4, forin: true, maxerr: 50, regexp: true, bitwise: true */
+/* global addEventListener, sessionStorage */
+(function() {
+    "use strict";
+
+    var SCROLL_KEY = "___bramble-preview-scrollTop::" + window.___brambleFilename;
+
+    // Retore last scroll position for this session (if any)
+    addEventListener("DOMContentLoaded", function() {
+        document.body.scrollTop = sessionStorage.getItem(SCROLL_KEY)|0;
+    }, false);
+
+    // Remember last scroll position for this document
+    addEventListener("scroll", function() {
+        sessionStorage.setItem(SCROLL_KEY, document.body.scrollTop);
+    }, false);
+}());

src/extensions/default/bramble/lib/Tutorial.js

@@ -39,7 +39,7 @@ define(function (require, exports, module) {
         return _tutorialOverride;
     }
 
-    function getUrl() {
+    function getPath() {
         return Path.join(StartupState.project("root"), "tutorial.html");
     }
 
@@ -47,7 +47,7 @@ define(function (require, exports, module) {
      * Callback returns `true` or `false`, like fs.exists().
      */
     function exists(callback) {
-        Filer.fs().stat(getUrl(), function(err, stats) {
+        Filer.fs().stat(getPath(), function(err, stats) {
             callback(stats && stats.type === "FILE");
         });
     }
@@ -61,7 +61,7 @@ define(function (require, exports, module) {
             return false;
         }
 
-        return getUrl() === editor.document.file.fullPath;
+        return getPath() === editor.document.file.fullPath;
     }
 
     /**
@@ -89,7 +89,7 @@ define(function (require, exports, module) {
 
     exports.setOverride = setOverride;
     exports.getOverride = getOverride;
-    exports.getUrl = getUrl;
+    exports.getPath = getPath;
     exports.exists = exists;
     exports.shouldReload = shouldReload;
     exports.shouldPostMessage = shouldPostMessage;

src/extensions/default/bramble/lib/launcher.js

@@ -68,7 +68,7 @@ define(function (require, exports, module) {
                 // Swap out the tutorial url and reload if necessary. We try hard
                 // not to reload unless we have to, so the tutorial doesn't flicker.
                 if(Tutorial.shouldReload()) {
-                    _launch(Tutorial.getUrl(), callback);
+                    _launch(Tutorial.getPath(), callback);
                 }
             }
         });

src/extensions/default/bramble/nohost/HTMLServer.js

@@ -10,8 +10,10 @@ define(function (require, exports, module) {
         Filer                   = brackets.getModule("filesystem/impls/filer/BracketsFiler"),
         Path                    = Filer.Path,
         HTMLRewriter            = brackets.getModule("filesystem/impls/filer/lib/HTMLRewriter"),
-        CSSRewriter             = brackets.getModule("filesystem/impls/filer/lib/CSSRewriter"),
-        Compatibility           = require("lib/compatibility");
+        CSSRewriter             = brackets.getModule("filesystem/impls/filer/lib/CSSRewriter");
+
+    var Compatibility           = require("lib/compatibility"),
+        ScrollManager           = require("lib/ScrollManager");
 
     var fs = Filer.fs(),
         _shouldUseBlobURL;
@@ -145,6 +147,9 @@ define(function (require, exports, module) {
                     return callback(err);
                 }
 
+                // Since we're not instrumenting this doc fully for some reason,
+                // at least inject the scroll manager so we can track scroll position.
+                body = body.replace(/<\/\s*head>/, ScrollManager.getRemoteScript(path) + "$&");
                 serve(body);
             });
         }