1 files changed, 89 insertions, 0 deletions
diff --git a/devtools/client/debugger/src/selectors/tabs.js b/devtools/client/debugger/src/selectors/tabs.js
new file mode 100644
index 0000000000..822bb7f49a
--- /dev/null
+++ b/devtools/client/debugger/src/selectors/tabs.js
@@ -0,0 +1,89 @@
+/* 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/>. */
+
+import { createSelector } from "devtools/client/shared/vendor/reselect";
+import { getPrettySourceURL } from "../utils/source";
+
+import { getSpecificSourceByURL } from "./sources";
+import { isSimilarTab } from "../utils/tabs";
+
+export const getTabs = state => state.tabs.tabs;
+
+// Return the list of tabs which relates to an active source
+export const getSourceTabs = createSelector(getTabs, tabs =>
+  tabs.filter(tab => tab.source)
+);
+
+export const getSourcesForTabs = createSelector(getSourceTabs, sourceTabs => {
+  return sourceTabs.map(tab => tab.source);
+});
+
+export function tabExists(state, sourceId) {
+  return !!getSourceTabs(state).find(tab => tab.source.id == sourceId);
+}
+
+export function hasPrettyTab(state, source) {
+  const prettyUrl = getPrettySourceURL(source.url);
+  return getTabs(state).some(tab => tab.url === prettyUrl);
+}
+
+/**
+ * Gets the next tab to select when a tab closes. Heuristics:
+ * 1. if the selected tab is available, it remains selected
+ * 2. if it is gone, the next available tab to the left should be active
+ * 3. if the first tab is active and closed, select the second tab
+ */
+export function getNewSelectedSource(state, tabList) {
+  const { selectedLocation } = state.sources;
+  const availableTabs = getTabs(state);
+  if (!selectedLocation) {
+    return null;
+  }
+
+  const selectedSource = selectedLocation.source;
+  if (!selectedSource) {
+    return null;
+  }
+
+  const matchingTab = availableTabs.find(tab =>
+    isSimilarTab(tab, selectedSource.url, selectedSource.isOriginal)
+  );
+
+  if (matchingTab) {
+    const specificSelectedSource = getSpecificSourceByURL(
+      state,
+      selectedSource.url,
+      selectedSource.isOriginal
+    );
+
+    if (specificSelectedSource) {
+      return specificSelectedSource;
+    }
+
+    return null;
+  }
+
+  const tabUrls = tabList.map(tab => tab.url);
+  const leftNeighborIndex = Math.max(
+    tabUrls.indexOf(selectedSource.url) - 1,
+    0
+  );
+  const lastAvailbleTabIndex = availableTabs.length - 1;
+  const newSelectedTabIndex = Math.min(leftNeighborIndex, lastAvailbleTabIndex);
+  const availableTab = availableTabs[newSelectedTabIndex];
+
+  if (availableTab) {
+    const tabSource = getSpecificSourceByURL(
+      state,
+      availableTab.url,
+      availableTab.isOriginal
+    );
+
+    if (tabSource) {
+      return tabSource;
+    }
+  }
+
+  return null;
+}