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+// Copyright 2010 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/**
+ * A class to hold information about the Codewalk Viewer.
+ * @param {jQuery} context The top element in whose context the viewer should
+ *     operate.  It will not touch any elements above this one.
+ * @constructor
+ */
+ var CodewalkViewer = function(context) {
+  this.context = context;
+
+  /**
+   * The div that contains all of the comments and their controls.
+   */
+  this.commentColumn = this.context.find('#comment-column');
+
+  /**
+   * The div that contains the comments proper.
+   */
+  this.commentArea = this.context.find('#comment-area');
+
+  /**
+   * The div that wraps the iframe with the code, as well as the drop down menu
+   * listing the different files.
+   * @type {jQuery}
+   */
+  this.codeColumn = this.context.find('#code-column');
+
+  /**
+   * The div that contains the code but excludes the options strip.
+   * @type {jQuery}
+   */
+  this.codeArea = this.context.find('#code-area');
+
+  /**
+   * The iframe that holds the code (from Sourcerer).
+   * @type {jQuery}
+   */
+  this.codeDisplay = this.context.find('#code-display');
+
+  /**
+   * The overlaid div used as a grab handle for sizing the code/comment panes.
+   * @type {jQuery}
+   */
+  this.sizer = this.context.find('#sizer');
+
+  /**
+   * The full-screen overlay that ensures we don't lose track of the mouse
+   * while dragging.
+   * @type {jQuery}
+   */
+  this.overlay = this.context.find('#overlay');
+
+  /**
+   * The hidden input field that we use to hold the focus so that we can detect
+   * shortcut keypresses.
+   * @type {jQuery}
+   */
+  this.shortcutInput = this.context.find('#shortcut-input');
+
+  /**
+   * The last comment that was selected.
+   * @type {jQuery}
+   */
+  this.lastSelected = null;
+};
+
+/**
+ * Minimum width of the comments or code pane, in pixels.
+ * @type {number}
+ */
+CodewalkViewer.MIN_PANE_WIDTH = 200;
+
+/**
+ * Navigate the code iframe to the given url and update the code popout link.
+ * @param {string} url The target URL.
+ * @param {Object} opt_window Window dependency injection for testing only.
+ */
+CodewalkViewer.prototype.navigateToCode = function(url, opt_window) {
+  if (!opt_window) opt_window = window;
+  // Each iframe is represented by two distinct objects in the DOM:  an iframe
+  // object and a window object.  These do not expose the same capabilities.
+  // Here we need to get the window representation to get the location member,
+  // so we access it directly through window[] since jQuery returns the iframe
+  // representation.
+  // We replace location rather than set so as not to create a history for code
+  // navigation.
+  opt_window['code-display'].location.replace(url);
+  var k = url.indexOf('&');
+  if (k != -1) url = url.slice(0, k);
+  k = url.indexOf('fileprint=');
+  if (k != -1) url = url.slice(k+10, url.length);
+  this.context.find('#code-popout-link').attr('href', url);
+};
+
+/**
+ * Selects the first comment from the list and forces a refresh of the code
+ * view.
+ */
+CodewalkViewer.prototype.selectFirstComment = function() {
+  // TODO(rsc): handle case where there are no comments
+  var firstSourcererLink = this.context.find('.comment:first');
+  this.changeSelectedComment(firstSourcererLink);
+};
+
+/**
+ * Sets the target on all links nested inside comments to be _blank.
+ */
+CodewalkViewer.prototype.targetCommentLinksAtBlank = function() {
+  this.context.find('.comment a[href], #description a[href]').each(function() {
+    if (!this.target) this.target = '_blank';
+  });
+};
+
+/**
+ * Installs event handlers for all the events we care about.
+ */
+CodewalkViewer.prototype.installEventHandlers = function() {
+  var self = this;
+
+  this.context.find('.comment')
+      .click(function(event) {
+        if (jQuery(event.target).is('a[href]')) return true;
+        self.changeSelectedComment(jQuery(this));
+        return false;
+      });
+
+  this.context.find('#code-selector')
+      .change(function() {self.navigateToCode(jQuery(this).val());});
+
+  this.context.find('#description-table .quote-feet.setting')
+      .click(function() {self.toggleDescription(jQuery(this)); return false;});
+
+  this.sizer
+      .mousedown(function(ev) {self.startSizerDrag(ev); return false;});
+  this.overlay
+      .mouseup(function(ev) {self.endSizerDrag(ev); return false;})
+      .mousemove(function(ev) {self.handleSizerDrag(ev); return false;});
+
+  this.context.find('#prev-comment')
+      .click(function() {
+          self.changeSelectedComment(self.lastSelected.prev()); return false;
+      });
+
+  this.context.find('#next-comment')
+      .click(function() {
+          self.changeSelectedComment(self.lastSelected.next()); return false;
+      });
+
+  // Workaround for Firefox 2 and 3, which steal focus from the main document
+  // whenever the iframe content is (re)loaded.  The input field is not shown,
+  // but is a way for us to bring focus back to a place where we can detect
+  // keypresses.
+  this.context.find('#code-display')
+      .load(function(ev) {self.shortcutInput.focus();});
+
+  jQuery(document).keypress(function(ev) {
+    switch(ev.which) {
+      case 110:  // 'n'
+          self.changeSelectedComment(self.lastSelected.next());
+          return false;
+      case 112:  // 'p'
+          self.changeSelectedComment(self.lastSelected.prev());
+          return false;
+      default:  // ignore
+    }
+  });
+
+  window.onresize = function() {self.updateHeight();};
+};
+
+/**
+ * Starts dragging the pane sizer.
+ * @param {Object} ev The mousedown event that started us dragging.
+ */
+CodewalkViewer.prototype.startSizerDrag = function(ev) {
+  this.initialCodeWidth = this.codeColumn.width();
+  this.initialCommentsWidth = this.commentColumn.width();
+  this.initialMouseX = ev.pageX;
+  this.overlay.show();
+};
+
+/**
+ * Handles dragging the pane sizer.
+ * @param {Object} ev The mousemove event updating dragging position.
+ */
+CodewalkViewer.prototype.handleSizerDrag = function(ev) {
+  var delta = ev.pageX - this.initialMouseX;
+  if (this.codeColumn.is('.right')) delta = -delta;
+  var proposedCodeWidth = this.initialCodeWidth + delta;
+  var proposedCommentWidth = this.initialCommentsWidth - delta;
+  var mw = CodewalkViewer.MIN_PANE_WIDTH;
+  if (proposedCodeWidth < mw) delta = mw - this.initialCodeWidth;
+  if (proposedCommentWidth < mw) delta = this.initialCommentsWidth - mw;
+  proposedCodeWidth = this.initialCodeWidth + delta;
+  proposedCommentWidth = this.initialCommentsWidth - delta;
+  // If window is too small, don't even try to resize.
+  if (proposedCodeWidth < mw || proposedCommentWidth < mw) return;
+  this.codeColumn.width(proposedCodeWidth);
+  this.commentColumn.width(proposedCommentWidth);
+  this.options.codeWidth = parseInt(
+      this.codeColumn.width() /
+      (this.codeColumn.width() + this.commentColumn.width()) * 100);
+  this.context.find('#code-column-width').text(this.options.codeWidth + '%');
+};
+
+/**
+ * Ends dragging the pane sizer.
+ * @param {Object} ev The mouseup event that caused us to stop dragging.
+ */
+CodewalkViewer.prototype.endSizerDrag = function(ev) {
+  this.overlay.hide();
+  this.updateHeight();
+};
+
+/**
+ * Toggles the Codewalk description between being shown and hidden.
+ * @param {jQuery} target The target that was clicked to trigger this function.
+ */
+CodewalkViewer.prototype.toggleDescription = function(target) {
+  var description = this.context.find('#description');
+  description.toggle();
+  target.find('span').text(description.is(':hidden') ? 'show' : 'hide');
+  this.updateHeight();
+};
+
+/**
+ * Changes the side of the window on which the code is shown and saves the
+ * setting in a cookie.
+ * @param {string?} codeSide The side on which the code should be, either
+ *     'left' or 'right'.
+ */
+CodewalkViewer.prototype.changeCodeSide = function(codeSide) {
+  var commentSide = codeSide == 'left' ? 'right' : 'left';
+  this.context.find('#set-code-' + codeSide).addClass('selected');
+  this.context.find('#set-code-' + commentSide).removeClass('selected');
+  // Remove previous side class and add new one.
+  this.codeColumn.addClass(codeSide).removeClass(commentSide);
+  this.commentColumn.addClass(commentSide).removeClass(codeSide);
+  this.sizer.css(codeSide, 'auto').css(commentSide, 0);
+  this.options.codeSide = codeSide;
+};
+
+/**
+ * Adds selected class to newly selected comment, removes selected style from
+ * previously selected comment, changes drop down options so that the correct
+ * file is selected, and updates the code popout link.
+ * @param {jQuery} target The target that was clicked to trigger this function.
+ */
+CodewalkViewer.prototype.changeSelectedComment = function(target) {
+  var currentFile = target.find('.comment-link').attr('href');
+  if (!currentFile) return;
+
+  if (!(this.lastSelected && this.lastSelected.get(0) === target.get(0))) {
+    if (this.lastSelected) this.lastSelected.removeClass('selected');
+    target.addClass('selected');
+    this.lastSelected = target;
+    var targetTop = target.position().top;
+    var parentTop = target.parent().position().top;
+    if (targetTop + target.height() > parentTop + target.parent().height() ||
+        targetTop < parentTop) {
+      var delta = targetTop - parentTop;
+      target.parent().animate(
+          {'scrollTop': target.parent().scrollTop() + delta},
+          Math.max(delta / 2, 200), 'swing');
+    }
+    var fname = currentFile.match(/(?:select=|fileprint=)\/[^&]+/)[0];
+    fname = fname.slice(fname.indexOf('=')+2, fname.length);
+    this.context.find('#code-selector').val(fname);
+    this.context.find('#prev-comment').toggleClass(
+        'disabled', !target.prev().length);
+    this.context.find('#next-comment').toggleClass(
+        'disabled', !target.next().length);
+  }
+
+  // Force original file even if user hasn't changed comments since they may
+  // have nagivated away from it within the iframe without us knowing.
+  this.navigateToCode(currentFile);
+};
+
+/**
+ * Updates the viewer by changing the height of the comments and code so that
+ * they fit within the height of the window.  The function is typically called
+ * after the user changes the window size.
+ */
+CodewalkViewer.prototype.updateHeight = function() {
+  var windowHeight = jQuery(window).height() - 5  // GOK
+  var areaHeight = windowHeight - this.codeArea.offset().top
+  var footerHeight = this.context.find('#footer').outerHeight(true)
+  this.commentArea.height(areaHeight - footerHeight - this.context.find('#comment-options').outerHeight(true))
+  var codeHeight = areaHeight - footerHeight - 15  // GOK
+  this.codeArea.height(codeHeight)
+  this.codeDisplay.height(codeHeight - this.codeDisplay.offset().top + this.codeArea.offset().top);
+  this.sizer.height(codeHeight);
+};
+
+jQuery(document).ready(function() {
+  var viewer = new CodewalkViewer(jQuery());
+  viewer.selectFirstComment();
+  viewer.targetCommentLinksAtBlank();
+  viewer.installEventHandlers();
+  viewer.updateHeight();
+});