add back button

Author: rsny430

src/system/CycleComputer.cpp

@@ -35,12 +35,14 @@ void CycleComputer::handleInput() {
             modeManager.nextMode();
             forceUpdate = true;
             break;
+        case InputEvent::BTN_B:
+            modeManager.prevMode();
+            forceUpdate = true;
+            break;
         case InputEvent::BTN_BOTH:
             tripComputer.reset();
             forceUpdate = true;
             break;
-        case InputEvent::BTN_B:
-            break;
         default:
             break;
     }

src/system/ModeManager.cpp

@@ -4,6 +4,10 @@ void ModeManager::nextMode() {
     currentMode = static_cast<Mode>((static_cast<int>(currentMode) + 1) % static_cast<int>(Mode::TOTAL_MODES));
 }
 
+void ModeManager::prevMode() {
+    currentMode = static_cast<Mode>((static_cast<int>(currentMode) - 1 + static_cast<int>(Mode::TOTAL_MODES)) % static_cast<int>(Mode::TOTAL_MODES));
+}
+
 Mode ModeManager::getMode() {
     return currentMode;
 }

src/system/ModeManager.h

@@ -8,5 +8,6 @@ class ModeManager {
 
    public:
     void nextMode();
+    void prevMode();
     Mode getMode();
 };

tests/host/ModeManagerTest.cpp

@@ -42,3 +42,35 @@ TEST_F(ModeManagerTest, CycleThroughModes) {
     mm.nextMode();
     EXPECT_EQ(mm.getMode(), Mode::SPEED);
 }
+
+TEST_F(ModeManagerTest, ReverseCycleThroughModes) {
+    ModeManager mm;
+
+    // SPEED -> AVG_SPEED (Wrap around backward)
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::AVG_SPEED);
+
+    // AVG_SPEED -> ELAPSED_TIME
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::ELAPSED_TIME);
+
+    // ELAPSED_TIME -> MOVING_TIME
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::MOVING_TIME);
+
+    // MOVING_TIME -> DISTANCE
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::DISTANCE);
+
+    // DISTANCE -> MAX_SPEED
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::MAX_SPEED);
+
+    // MAX_SPEED -> TIME
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::TIME);
+
+    // TIME -> SPEED
+    mm.prevMode();
+    EXPECT_EQ(mm.getMode(), Mode::SPEED);
+}