feat: HIIT countdown timer with auto set/rest cycling

app/src/main/java/org/librefit/db/AppDatabase.kt

@@ -27,7 +27,7 @@ import org.librefit.db.entity.Workout
 
 @Database(
     entities = [Workout::class, Exercise::class, Set::class, Measurement::class, ExerciseDC::class],
-    version = 3,
+    version = 4,
     exportSchema = true,
     autoMigrations = [
         AutoMigration(from = 1, to = 2)
@@ -38,6 +38,31 @@ abstract class AppDatabase : RoomDatabase() {
     companion object {
         const val NAME = "librefit_database"
 
+        val MIGRATION_3_4 = object : Migration(3, 4) {
+            override fun migrate(db: SupportSQLiteDatabase) {
+                // Add HIIT countdown fields to exercises table
+                db.execSQL(
+                    """
+                    ALTER TABLE exercises
+                    ADD COLUMN targetDuration INTEGER NOT NULL DEFAULT 0
+                    """.trimIndent()
+                )
+                db.execSQL(
+                    """
+                    ALTER TABLE exercises
+                    ADD COLUMN autoAdvanceSets INTEGER NOT NULL DEFAULT 0
+                    """.trimIndent()
+                )
+                // Add cautions field to dataset (ExerciseDC) table
+                db.execSQL(
+                    """
+                    ALTER TABLE dataset
+                    ADD COLUMN cautions TEXT NOT NULL DEFAULT ''
+                    """.trimIndent()
+                )
+            }
+        }
+
         val MIGRATION_2_3 = object : Migration(2, 3) {
             override fun migrate(db: SupportSQLiteDatabase) {
                 db.execSQL(

app/src/main/java/org/librefit/db/entity/Exercise.kt

@@ -67,5 +67,9 @@ data class Exercise(
     val setMode: SetMode = SetMode.LOAD,
     val restTime: Int = 0,
     val position: Int = 0,
-    val workoutId: Long = 0// Foreign key reference to Workout
+    val workoutId: Long = 0,// Foreign key reference to Workout
+    /** Target duration in seconds for DURATION sets used in countdown mode (HIIT). 0 = use stopwatch instead. */
+    val targetDuration: Int = 0,
+    /** When true, sets auto-advance: countdown → rest → next set countdown, without user input. */
+    val autoAdvanceSets: Boolean = false
 )

app/src/main/java/org/librefit/db/entity/ExerciseDC.kt

@@ -199,5 +199,7 @@ data class ExerciseDC(
     val instructions: List<String> = listOf(),
     val category: Category = Category.POWERLIFTING,
     val images: List<String> = listOf(),
-    val isCustomExercise: Boolean = false
+    val isCustomExercise: Boolean = false,
+    /** Common mistakes and cautions for the exercise (user-facing text). */
+    val cautions: String = ""
 )

app/src/main/java/org/librefit/di/DatabaseModule.kt

@@ -35,7 +35,7 @@ object DatabaseModule {
             AppDatabase::class.java,
             AppDatabase.NAME
         )
-            .addMigrations(AppDatabase.MIGRATION_2_3)
+            .addMigrations(AppDatabase.MIGRATION_2_3, AppDatabase.MIGRATION_3_4)
             .build()
     }
 

app/src/main/java/org/librefit/enums/WorkoutServiceActions.kt

@@ -15,5 +15,9 @@ enum class WorkoutServiceActions(val string: String) {
     MODIFY_REST_TIMER("PAUSE_REST_TIMER"),
     WORKOUT_FOCUS("WORKOUT_FOCUS"),
     STOP_SERVICE("STOP_SERVICE"),
-    SET_ELAPSED_TIME("SET_ELAPSED_TIME")
+    SET_ELAPSED_TIME("SET_ELAPSED_TIME"),
+    /** Start a HIIT countdown timer (counts down from targetDuration to 0). */
+    START_COUNTDOWN("START_COUNTDOWN"),
+    /** Cancel an active countdown without advancing to rest. */
+    CANCEL_COUNTDOWN("CANCEL_COUNTDOWN")
 }

app/src/main/java/org/librefit/services/WorkoutService.kt

@@ -86,14 +86,39 @@ class WorkoutService : Service() {
         private val _restTime = MutableStateFlow(0)
         val restTime: StateFlow<Int> = _restTime
 
+        /** Countdown timer for HIIT sets (counts down to 0). */
+        private val _countdownTime = MutableStateFlow(0)
+        val countdownTime: StateFlow<Int> = _countdownTime
+
+        /** Whether a HIIT countdown is actively running. */
+        private val _isCountdownActive = MutableStateFlow(false)
+        val isCountdownActive: StateFlow<Boolean> = _isCountdownActive
+
+        /** Total duration for the current countdown (used for progress calculation). */
+        private val _countdownTotal = MutableStateFlow(0)
+        val countdownTotal: StateFlow<Int> = _countdownTotal
+
+        /** Emits true once when a countdown finishes — consumed by the ViewModel to auto-start rest. */
+        private val _countdownFinished = MutableStateFlow(false)
+        val countdownFinished: StateFlow<Boolean> = _countdownFinished
+
         const val EXTRA_INITIAL_REST_TIME = "EXTRA_INITIAL_REST_TIME"
         const val EXTRA_ADD_TEN_SECONDS = "EXTRA_ADD_TEN_SECONDS"
         const val EXTRA_IS_FOCUSED = "EXTRA_IS_FOCUSED"
         const val EXTRA_SET_ELAPSED_TIME = "EXTRA_SET_ELAPSED_TIME"
+        const val EXTRA_COUNTDOWN_DURATION = "EXTRA_COUNTDOWN_DURATION"
+        /** Rest duration to auto-start after countdown finishes (0 = skip rest). */
+        const val EXTRA_COUNTDOWN_REST_DURATION = "EXTRA_COUNTDOWN_REST_DURATION"
+
+        /** Acknowledge the [countdownFinished] signal (call from ViewModel after reading it). */
+        fun clearCountdownFinished() {
+            _countdownFinished.update { false }
+        }
     }
 
     private var initialRestTime = 0
     private var isFocused = true
+    private var countdownRestDuration = 0
 
     @Inject
     lateinit var notificationHelper: NotificationHelper
@@ -145,6 +170,24 @@ class WorkoutService : Service() {
                     it + (intent?.getIntExtra(EXTRA_SET_ELAPSED_TIME, 0) ?: 0)
                 }
             }
+
+            WorkoutServiceActions.START_COUNTDOWN -> {
+                val duration = intent?.getIntExtra(EXTRA_COUNTDOWN_DURATION, 0) ?: 0
+                countdownRestDuration =
+                    intent?.getIntExtra(EXTRA_COUNTDOWN_REST_DURATION, 0) ?: 0
+                countdownJob?.cancel()
+                _countdownTotal.update { duration }
+                _countdownTime.update { duration }
+                _isCountdownActive.update { true }
+                _countdownFinished.update { false }
+                startCountdown()
+            }
+
+            WorkoutServiceActions.CANCEL_COUNTDOWN -> {
+                countdownJob?.cancel()
+                _isCountdownActive.update { false }
+                _countdownTime.update { 0 }
+            }
         }
 
         return START_STICKY
@@ -153,9 +196,15 @@ class WorkoutService : Service() {
     fun stopService() {
         stopwatchJob?.cancel()
         restTimerJob?.cancel()
+        countdownJob?.cancel()
         _timeElapsed.update { 0 }
         _restTime.update { 0 }
+        _countdownTime.update { 0 }
+        _isCountdownActive.update { false }
+        _countdownFinished.update { false }
+        _countdownTotal.update { 0 }
         initialRestTime = 0
+        countdownRestDuration = 0
         stopForeground(STOP_FOREGROUND_REMOVE)
         stopSelf()
     }
@@ -200,6 +249,34 @@ class WorkoutService : Service() {
     }
 
 
+    private var countdownJob: Job? = null
+
+    /**
+     * HIIT countdown: counts from [countdownTime] down to 0, then:
+     * 1. Signals [countdownFinished] for the ViewModel
+     * 2. Auto-starts the rest timer if [countdownRestDuration] > 0
+     */
+    private fun startCountdown() {
+        countdownJob = serviceScope.launch {
+            while (countdownTime.value > 0) {
+                delay(1000)
+                _countdownTime.update { (it - 1).coerceAtLeast(0) }
+            }
+            _isCountdownActive.update { false }
+            _countdownFinished.update { true }
+
+            // Auto-start rest if configured
+            if (countdownRestDuration > 0) {
+                restTimerJob?.cancel()
+                initialRestTime = countdownRestDuration
+                _restTime.update { countdownRestDuration }
+                startRestTimer()
+            }
+        }
+    }
+
+
+
     private var restTimerJob: Job? = null
 
     private fun startRestTimer() {

app/src/main/java/org/librefit/services/WorkoutServiceManager.kt

@@ -13,6 +13,8 @@ import android.content.Intent
 import dagger.hilt.android.qualifiers.ApplicationContext
 import org.librefit.enums.WorkoutServiceActions
 import org.librefit.services.WorkoutService.Companion.EXTRA_ADD_TEN_SECONDS
+import org.librefit.services.WorkoutService.Companion.EXTRA_COUNTDOWN_DURATION
+import org.librefit.services.WorkoutService.Companion.EXTRA_COUNTDOWN_REST_DURATION
 import org.librefit.services.WorkoutService.Companion.EXTRA_INITIAL_REST_TIME
 import org.librefit.services.WorkoutService.Companion.EXTRA_IS_FOCUSED
 import org.librefit.services.WorkoutService.Companion.EXTRA_SET_ELAPSED_TIME
@@ -73,6 +75,26 @@ class WorkoutServiceManager @Inject constructor(
         context.startForegroundService(serviceIntent)
     }
 
+    /**
+     * Start a HIIT countdown timer that counts down from [durationSeconds] to 0,
+     * then auto-starts rest timer for [restDurationSeconds] if > 0.
+     */
+    fun startCountdown(durationSeconds: Int, restDurationSeconds: Int) {
+        val serviceIntent = workoutServiceIntent.apply {
+            action = WorkoutServiceActions.START_COUNTDOWN.string
+            putExtra(EXTRA_COUNTDOWN_DURATION, durationSeconds)
+            putExtra(EXTRA_COUNTDOWN_REST_DURATION, restDurationSeconds)
+        }
+        context.startForegroundService(serviceIntent)
+    }
+
+    fun cancelCountdown() {
+        val serviceIntent = workoutServiceIntent.apply {
+            action = WorkoutServiceActions.CANCEL_COUNTDOWN.string
+        }
+        context.startForegroundService(serviceIntent)
+    }
+
     fun stopService() {
         val serviceIntent = workoutServiceIntent.apply {
             action = WorkoutServiceActions.STOP_SERVICE.string