Bug 1309194: Implement summary info in Net Panel Toolbar; Bug 1317205: CSS improvement for summary button

Required for: https://github.com/MoonchildProductions/moebius/pull/93

devtools/client/netmonitor/selectors/index.js

@@ -1,8 +1,63 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
 "use strict";
 
+const { createSelector } = require("devtools/client/shared/vendor/reselect");
+
+/**
+ * Gets the total number of bytes representing the cumulated content size of
+ * a set of requests. Returns 0 for an empty set.
+ *
+ * @param {array} items - an array of request items
+ * @return {number} total bytes of requests
+ */
+function getTotalBytesOfRequests(items) {
+  if (!items.length) {
+    return 0;
+  }
+
+  let result = 0;
+  items.forEach((item) => {
+    let size = item.attachment.contentSize;
+    result += (typeof size == "number") ? size : 0;
+  });
+
+  return result;
+}
+
+/**
+ * Gets the total milliseconds for all requests. Returns null for an
+ * empty set.
+ *
+ * @param {array} items - an array of request items
+ * @return {object} total milliseconds for all requests
+ */
+function getTotalMillisOfRequests(items) {
+  if (!items.length) {
+    return null;
+  }
+
+  const oldest = items.reduce((prev, curr) =>
+    prev.attachment.startedMillis < curr.attachment.startedMillis ?
+      prev : curr);
+  const newest = items.reduce((prev, curr) =>
+    prev.attachment.startedMillis > curr.attachment.startedMillis ?
+      prev : curr);
+
+  return newest.attachment.endedMillis - oldest.attachment.startedMillis;
+}
+
+const getSummary = createSelector(
+  (state) => state.requests.items,
+  (requests) => ({
+    count: requests.length,
+    totalBytes: getTotalBytesOfRequests(requests),
+    totalMillis: getTotalMillisOfRequests(requests),
+  })
+);
+
 module.exports = {
-  // selectors...
+  getSummary,
 };