fix(timer): significantly reduce recomposition count (by ~90%)

This improves the performance and perceived smoothness of the timer screen by a lot

app/src/main/java/org/nsh07/pomodoro/ui/AppScreen.kt

@@ -45,7 +45,6 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
-import androidx.compose.runtime.rememberUpdatedState
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
@@ -79,9 +78,7 @@ fun AppScreen(
     val context = LocalContext.current
 
     val uiState by timerViewModel.timerState.collectAsStateWithLifecycle()
-    val remainingTime by timerViewModel.time.collectAsStateWithLifecycle()
-
-    val progress by rememberUpdatedState((uiState.totalTime.toFloat() - remainingTime) / uiState.totalTime)
+    val progress by timerViewModel.progress.collectAsStateWithLifecycle()
 
     val layoutDirection = LocalLayoutDirection.current
     val motionScheme = motionScheme

app/src/main/java/org/nsh07/pomodoro/ui/timerScreen/viewModel/TimerViewModel.kt

@@ -30,8 +30,11 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.FlowPreview
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import org.nsh07.pomodoro.TomatoApplication
@@ -55,6 +58,12 @@ class TimerViewModel(
     val timerState: StateFlow<TimerState> = _timerState.asStateFlow()
 
     val time: StateFlow<Long> = _time.asStateFlow()
+
+    val progress = _time.map {
+        val uiState = timerState.value
+        (uiState.totalTime.toFloat() - it) / uiState.totalTime
+    }.stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), 0f)
+
     private var cycles = 0
 
     private var startTime = 0L