Issue #3557: Add TabListAction.RestoreAction for restoring a list of tabs and the selection.

components/browser/state/src/main/java/mozilla/components/browser/state/action/BrowserAction.kt

@@ -16,7 +16,6 @@ import mozilla.components.lib.state.Action
  * [Action] implementation related to [BrowserState].
  */
 sealed class BrowserAction : Action
-
 /**
  * [BrowserAction] implementations related to updating the list of [TabSessionState] inside [BrowserState].
  */
@@ -35,6 +34,11 @@ sealed class TabListAction : BrowserAction() {
      * Removes the [TabSessionState] with the given [tabId] from the list of sessions.
      */
     data class RemoveTabAction(val tabId: String) : TabListAction()
+
+    /**
+     * Restores state from a (partial) previous state.
+     */
+    data class RestoreAction(val tabs: List<TabSessionState>, val selectedTabId: String? = null) : TabListAction()
 }
 
 /**

components/browser/state/src/main/java/mozilla/components/browser/state/reducer/TabListReducer.kt

@@ -51,6 +51,23 @@ internal object TabListReducer {
                     )
                 }
             }
+
+            is TabListAction.RestoreAction -> {
+                // We are adding the restored tabs first and then the already existing tabs. Since restore can or should
+                // happen asynchronously we may already have a tab at this point (e.g. from an `Intent` and so we
+                // pretend we restored the list of tabs before any tab was added.
+                state.copy(
+                    tabs = action.tabs + state.tabs,
+                    selectedTabId = if (action.selectedTabId != null && state.selectedTabId == null) {
+                        // We only want to update the selected tab if none has been already selected. Otherwise we may
+                        // switch to a restored tab even though the user is already looking at an existing tab (e.g.
+                        // a tab that came from an intent).
+                        action.selectedTabId
+                    } else {
+                        state.selectedTabId
+                    }
+                )
+            }
         }
     }
 }

components/browser/state/src/test/java/mozilla/components/browser/state/action/TabListActionTest.kt

@@ -258,4 +258,110 @@ class TabListActionTest {
         store.dispatch(TabListAction.RemoveTabAction("a")).joinBlocking()
         assertNull(store.state.selectedTabId)
     }
+
+    @Test
+    fun `RestoreAction - Adds restored tabs and updates selected tab`() {
+        val store = BrowserStore(BrowserState())
+
+        assertEquals(0, store.state.tabs.size)
+
+        store.dispatch(TabListAction.RestoreAction(
+            tabs = listOf(
+                createTab(id = "a", url = "https://www.mozilla.org", private = false),
+                createTab(id = "b", url = "https://www.firefox.com", private = true),
+                createTab(id = "c", url = "https://www.example.org", private = true),
+                createTab(id = "d", url = "https://getpocket.com", private = false)
+            ),
+            selectedTabId = "d"
+        )).joinBlocking()
+
+        assertEquals(4, store.state.tabs.size)
+        assertEquals("a", store.state.tabs[0].id)
+        assertEquals("b", store.state.tabs[1].id)
+        assertEquals("c", store.state.tabs[2].id)
+        assertEquals("d", store.state.tabs[3].id)
+        assertEquals("d", store.state.selectedTabId)
+    }
+
+    @Test
+    fun `RestoreAction - Adds restored tabs to existing tabs without updating selection`() {
+        val store = BrowserStore(BrowserState(
+            tabs = listOf(
+                createTab(id = "a", url = "https://www.mozilla.org", private = false),
+                createTab(id = "b", url = "https://www.firefox.com", private = true)
+            ),
+            selectedTabId = "a"
+        ))
+
+        assertEquals(2, store.state.tabs.size)
+
+        store.dispatch(TabListAction.RestoreAction(
+            tabs = listOf(
+                createTab(id = "c", url = "https://www.example.org", private = true),
+                createTab(id = "d", url = "https://getpocket.com", private = false)
+            ),
+            selectedTabId = "d"
+        )).joinBlocking()
+
+        assertEquals(4, store.state.tabs.size)
+        assertEquals("c", store.state.tabs[0].id)
+        assertEquals("d", store.state.tabs[1].id)
+        assertEquals("a", store.state.tabs[2].id)
+        assertEquals("b", store.state.tabs[3].id)
+        assertEquals("a", store.state.selectedTabId)
+    }
+
+    @Test
+    fun `RestoreAction - Adds restored tabs to existing tabs with updating selection`() {
+        val store = BrowserStore(BrowserState(
+            tabs = listOf(
+                createTab(id = "a", url = "https://www.mozilla.org", private = false),
+                createTab(id = "b", url = "https://www.firefox.com", private = true)
+            )
+        ))
+
+        assertEquals(2, store.state.tabs.size)
+
+        store.dispatch(TabListAction.RestoreAction(
+            tabs = listOf(
+                createTab(id = "c", url = "https://www.example.org", private = true),
+                createTab(id = "d", url = "https://getpocket.com", private = false)
+            ),
+            selectedTabId = "d"
+        )).joinBlocking()
+
+        assertEquals(4, store.state.tabs.size)
+        assertEquals("c", store.state.tabs[0].id)
+        assertEquals("d", store.state.tabs[1].id)
+        assertEquals("a", store.state.tabs[2].id)
+        assertEquals("b", store.state.tabs[3].id)
+        assertEquals("d", store.state.selectedTabId)
+    }
+
+    @Test
+    fun `RestoreAction - Does not update selection if none was provided`() {
+        val store = BrowserStore(BrowserState(
+            tabs = listOf(
+                createTab(id = "a", url = "https://www.mozilla.org", private = false),
+                createTab(id = "b", url = "https://www.firefox.com", private = true)
+            )
+        ))
+
+        assertEquals(2, store.state.tabs.size)
+
+        store.dispatch(TabListAction.RestoreAction(
+            tabs = listOf(
+                createTab(id = "c", url = "https://www.example.org", private = true),
+                createTab(id = "d", url = "https://getpocket.com", private = false)
+            ),
+            selectedTabId = null
+        )).joinBlocking()
+
+        assertEquals(4, store.state.tabs.size)
+        assertEquals("c", store.state.tabs[0].id)
+        assertEquals("d", store.state.tabs[1].id)
+        assertEquals("a", store.state.tabs[2].id)
+        assertEquals("b", store.state.tabs[3].id)
+        assertNull(store.state.selectedTabId)
+    }
 }