Issue 7450 - Implement hide-if-contains-visible-text snippet

lib/content/snippets.js

Index: lib/content/snippets.js
===================================================================
--- a/lib/content/snippets.js
+++ b/lib/content/snippets.js
@@ -900,8 +900,85 @@
     }
 
     return fetch_.apply(this, args);
   };
 }
 
 exports["strip-fetch-query-parameter"] = makeInjector(stripFetchQueryParameter,
                                                       toRegExp, regexEscape);
+
+function hideIfContainsVisibleText(search, hideSelector, innerSelector = null)
+{
+  /**
+   * Determine if the text inside the element is visible.
+   * @param {Element} element the leaf element we are checking.
+   * @param {?CSSStyle} style the computed style of element.
+   * @returns {bool} whether the text is visible.
+   */
+  function isTextVisible(element, style)
+  {
+    if (!style)
+      style = window.getComputedStyle(element);
+
+    if (style.getPropertyValue("opacity") == "0")
+      return false;
+    if (style.getPropertyValue("font-size") == "0px")
+      return false;
+    if (style.getPropertyValue("color") ==
+        style.getPropertyValue("background-color"))
+      return false;
+
+    return true;
+  }
+
+  /**
+   * Returns the visible text content from an element and its children.
+   * @param {Element} element the element whose visible text we want.
+   * @returns {String} the text that is visible.
+   */
+  function getVisibleContent(element)
+  {
+    let style = window.getComputedStyle(element);
+    if (style.getPropertyValue("display") == "none")
+      return "";
+    let visibility = style.getPropertyValue("visibility");
+    if (visibility == "hidden" || visibility == "collapse")
+      return "";
+
+    let text = "";
+    for (let node of element.childNodes)
+    {
+      switch (node.nodeType)
+      {
+        case Node.ELEMENT_NODE:
+          text += getVisibleContent(node);
+          break;
+        case Node.TEXT_NODE:
+          if (isTextVisible(element, style))
+            text += node.nodeValue;
+          break;
+      }
+    }
+    return text;
+  }
+
+  let re = toRegExp(search);
+
+  new MutationObserver(() =>
+  {
+    for (let element of document.querySelectorAll(hideSelector))
+    {
+      let inners =
+          innerSelector ? element.querySelectorAll(innerSelector) : [element];
+      for (let inner of inners)
+      {
+        let content = getVisibleContent(inner);
+        if (re.test(content))
+          hideElement(element);
+      }
+    }
+  })
+  .observe(document, {childList: true, characterData: true, subtree: true});
+}
+
+exports["hide-if-contains-visible-text"] =
+  makeInjector(hideIfContainsVisibleText, hideElement);