Issue 2879 - Move element selection into the content process

lib/child/utils.js

Index: lib/child/utils.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/child/utils.js
@@ -0,0 +1,119 @@
+/*
+ * This Source Code is subject to the terms of the Mozilla Public License
+ * version 2.0 (the "License"). You can obtain a copy of the License at
+ * http://mozilla.org/MPL/2.0/.
+ */
+
+"use strict";
+
+/**
+ * Element creation helper, allows defining attributes and child elements in one
+ * go.
+ * @param {Document} doc
+ *   Document to create the element in
+ * @param {string} tagName
+ *   Tag name of the new element
+ * @param {Object.<string, string>} [attrs]
+ *   Attributes to set on the element
+ * @param {Array.<Node>} [children]
+ *   Child nodes to add to the element
+ * @return {Element}
+ *   Element that was created
+ */
+function createElement(doc, tagName, attrs, children)
+{
+  let el = doc.createElement(tagName);
+  if (attrs)
+    for (let key in attrs)
+      el.setAttribute(key, attrs[key]);
+  if (children)
+    for (let child of children)
+      el.appendChild(child)
+  return el;
+}
+exports.createElement = createElement;
+
+/**
+ * Calculates the document size for a window.
+ * @return {Array.<number>}
+ *   Width and height of the document loaded into the window
+ */
+function getWindowSize(/**Window*/ wnd)
+{
+  return [wnd.innerWidth, wnd.document.documentElement.clientHeight];
+}
+exports.getWindowSize = getWindowSize;
+
+/**
+ * Determines the parent element for a document node, if any. Will ascend into
+ * parent frames if necessary.
+ */
+function getParentElement(/**Node*/ elem) /**Element*/
+{
+  let result = elem.parentNode;
+  if (result && result.nodeType == result.DOCUMENT_NODE && result.defaultView && result.defaultView.frameElement)
+    result = result.defaultView.frameElement;
+
+  if (result && result.nodeType != result.ELEMENT_NODE)
+    return null;
+
+  return result;
+}
+exports.getParentElement = getParentElement;
+
+/**
+ * Modifies a rectangle with coordinates relative to a window's client area
+ * to make sure it doesn't exceed that client area.
+ * @param {Object} rect
+ *   Rectangle with properties left, top, right, bottom.
+ * @param {Window} wnd
+ *   Window to restrict the rectangle to.
+ */
+function intersectRect(rect, wnd)
+{
+  let [wndWidth, wndHeight] = getWindowSize(wnd);
+  rect.left = Math.max(rect.left, 0);
+  rect.top = Math.max(rect.top, 0);
+  rect.right = Math.min(rect.right, wndWidth);
+  rect.bottom = Math.min(rect.bottom, wndHeight);
+}
+
+/**
+ * Calculates the element's position within the top frame. This will consider
+ * the element being clipped by frame boundaries.
+ * @return {Object}
+ *   Object with properties left, top, width, height denoting the element's
+ *   position and size within the top frame.
+ */
+function getElementPosition(/**Element*/ element)
+{
+  let rect = element.getBoundingClientRect();
+  let wnd = element.ownerDocument.defaultView;
+
+  rect = {left: rect.left, top: rect.top,
+          right: rect.right, bottom: rect.bottom};
+  while (true)
+  {
+    intersectRect(rect, wnd);
+
+    if (!wnd.frameElement)
+      break;
+
+    // Recalculate coordinates to be relative to frame's parent window
+    let frameElement = wnd.frameElement;
+    wnd = frameElement.ownerDocument.defaultView;
+
+    let frameRect = frameElement.getBoundingClientRect();
+    let frameStyle = wnd.getComputedStyle(frameElement, null);
+    let relLeft = frameRect.left + parseFloat(frameStyle.borderLeftWidth) + parseFloat(frameStyle.paddingLeft);
+    let relTop = frameRect.top + parseFloat(frameStyle.borderTopWidth) + parseFloat(frameStyle.paddingTop);
+
+    rect.left += relLeft;
+    rect.right += relLeft;
+    rect.top += relTop;
+    rect.bottom += relTop;
+  }
+
+  return rect;
+}
+exports.getElementPosition = getElementPosition;