2 files changed, 77 insertions, 0 deletions
diff --git a/devtools/shared/commands/target/reducers/moz.build b/devtools/shared/commands/target/reducers/moz.build
new file mode 100644
index 0000000000..e9429c1200
--- /dev/null
+++ b/devtools/shared/commands/target/reducers/moz.build
@@ -0,0 +1,7 @@
+# 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/.
+
+DevToolsModules(
+    "targets.js",
+)
diff --git a/devtools/shared/commands/target/reducers/targets.js b/devtools/shared/commands/target/reducers/targets.js
new file mode 100644
index 0000000000..2e93ddd7f0
--- /dev/null
+++ b/devtools/shared/commands/target/reducers/targets.js
@@ -0,0 +1,70 @@
+/* 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 initialReducerState = {
+  // Array of targetFront
+  targets: [],
+  // The selected targetFront instance
+  selected: null,
+  // timestamp of the last time a target was updated (i.e. url/title was updated).
+  // This is used by the EvaluationContextSelector component to re-render the list of
+  // targets when the list itself did not change (no addition/removal)
+  lastTargetRefresh: Date.now(),
+};
+
+function update(state = initialReducerState, action) {
+  switch (action.type) {
+    case "SELECT_TARGET": {
+      const { targetActorID } = action;
+
+      if (state.selected?.actorID === targetActorID) {
+        return state;
+      }
+
+      const selectedTarget = state.targets.find(
+        target => target.actorID === targetActorID
+      );
+
+      // It's possible that the target reducer is missing a target
+      // e.g. workers, remote iframes, etc. (Bug 1594754)
+      if (!selectedTarget) {
+        return state;
+      }
+
+      return { ...state, selected: selectedTarget };
+    }
+
+    case "REGISTER_TARGET": {
+      return {
+        ...state,
+        targets: [...state.targets, action.targetFront],
+      };
+    }
+
+    case "REFRESH_TARGETS": {
+      // The data _in_ targetFront was updated, so we only need to mutate the state,
+      // while keeping the same values.
+      return {
+        ...state,
+        lastTargetRefresh: Date.now(),
+      };
+    }
+
+    case "UNREGISTER_TARGET": {
+      const targets = state.targets.filter(
+        target => target !== action.targetFront
+      );
+
+      let { selected } = state;
+      if (selected === action.targetFront) {
+        selected = null;
+      }
+
+      return { ...state, targets, selected };
+    }
+  }
+  return state;
+}
+module.exports = update;