refactor: implements QuickBarStateMachine to drive UI update of QuickBar

Author: WhiredPlanck

app/src/main/java/com/osfans/trime/ime/bar/QuickBar.kt

@@ -93,21 +93,17 @@ class QuickBar(
         TabUi(context)
     }
 
-    override fun onInputContextUpdate(ctx: RimeProto.Context) {
-        if (ctx.composition.length > 0) {
-            switchUiByState(State.Candidate)
-        } else {
-            switchUiByState(State.Always)
-        }
+    private val barStateMachine = QuickBarStateMachine.new {
+        switchUiByState(it)
     }
 
-    enum class State {
-        Always,
-        Candidate,
-        Tab,
+    override fun onInputContextUpdate(ctx: RimeProto.Context) {
+        barStateMachine.push(
+            QuickBarStateMachine.TransitionEvent.CandidatesUpdated,
+            QuickBarStateMachine.BooleanKey.CandidateEmpty to ctx.menu.candidates.isEmpty())
     }
 
-    private fun switchUiByState(state: State) {
+    private fun switchUiByState(state: QuickBarStateMachine.State) {
         val index = state.ordinal
         if (view.displayedChild == index) return
         val new = view.getChildAt(index)
@@ -176,13 +172,11 @@ class QuickBar(
     override fun onWindowAttached(window: BoardWindow) {
         if (window is BoardWindow.BarBoardWindow) {
             window.onCreateBarView()?.let { tabUi.addExternal(it) }
-            switchUiByState(State.Tab)
-        } else {
-            switchUiByState(State.Always)
+            barStateMachine.push(QuickBarStateMachine.TransitionEvent.BarBoardWindowAttached)
         }
     }
 
     override fun onWindowDetached(window: BoardWindow) {
-        switchUiByState(State.Candidate)
+        barStateMachine.push(QuickBarStateMachine.TransitionEvent.WindowDetached)
     }
 }

app/src/main/java/com/osfans/trime/ime/bar/QuickBarStateMachine.kt

@@ -0,0 +1,53 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ * SPDX-FileCopyrightText: Copyright 2021-2023 Fcitx5 for Android Contributors
+ */
+package com.osfans.trime.ime.bar
+
+import com.osfans.trime.ime.bar.QuickBarStateMachine.BooleanKey.CandidateEmpty
+import com.osfans.trime.ime.bar.QuickBarStateMachine.State.Always
+import com.osfans.trime.ime.bar.QuickBarStateMachine.State.Candidate
+import com.osfans.trime.ime.bar.QuickBarStateMachine.State.Tab
+import com.osfans.trime.util.BuildTransitionEvent
+import com.osfans.trime.util.EventStateMachine
+import com.osfans.trime.util.TransitionBuildBlock
+
+object QuickBarStateMachine {
+    enum class State {
+        Always,
+        Candidate,
+        Tab,
+    }
+
+    enum class BooleanKey : EventStateMachine.BooleanStateKey {
+        CandidateEmpty,
+    }
+
+    enum class TransitionEvent(val builder: TransitionBuildBlock<State, BooleanKey>) :
+        EventStateMachine.TransitionEvent<State, BooleanKey> by BuildTransitionEvent(builder) {
+        CandidatesUpdated({
+            from(Always) transitTo Candidate on (CandidateEmpty to false)
+            from(Candidate) transitTo Always on (CandidateEmpty to true)
+        }),
+        BarBoardWindowAttached({
+            from(Always) transitTo Tab
+            from(Candidate) transitTo Tab
+        }),
+        WindowDetached({
+            // candidate state has higher priority so here it goes first
+            from(Tab) transitTo Candidate on (CandidateEmpty to false)
+            from(Tab) transitTo Always
+        }),
+    }
+
+    fun new(block: (State) -> Unit) =
+        EventStateMachine<State, TransitionEvent, BooleanKey>(
+            initialState = Always,
+            externalBooleanStates =
+                mutableMapOf(
+                    CandidateEmpty to true,
+                ),
+        ).apply {
+            onNewStateListener = block
+        }
+}