🚀 Accident scroll prevention

* Now every time you bring bars, a new checkpoint saves
* Checkpoint restores exact position
* Visual indication of checkpoint position on slider track
* Arrow in the direction of checkpoint when changed position

Resolves: #61

app/src/main/java/ua/acclorite/book_story/domain/util/Direction.kt

@@ -0,0 +1,8 @@
+package ua.acclorite.book_story.domain.util
+
+import androidx.compose.runtime.Immutable
+
+@Immutable
+enum class Direction {
+    START, NEUTRAL, END
+}

app/src/main/java/ua/acclorite/book_story/presentation/core/util/Functions.kt

@@ -34,3 +34,11 @@ fun Intent.launchActivity(
 
     success?.invoke()
 }
+
+fun Float.calculateProgress(digits: Int): String {
+    return (this * 100)
+        .toDouble()
+        .removeDigits(digits)
+        .removeTrailingZero()
+        .dropWhile { it == '-' }
+}

app/src/main/java/ua/acclorite/book_story/presentation/data/MainViewModel.kt

@@ -169,7 +169,10 @@ class MainViewModel @Inject constructor(
 
             is MainEvent.OnChangeParagraphIndentation -> {
                 viewModelScope.launch(Dispatchers.IO) {
-                    setDatastore.execute(DataStoreConstants.PARAGRAPH_INDENTATION, event.indentation)
+                    setDatastore.execute(
+                        DataStoreConstants.PARAGRAPH_INDENTATION,
+                        event.indentation
+                    )
                     updateStateWithSavedHandle {
                         it.copy(
                             paragraphIndentation = event.indentation

app/src/main/java/ua/acclorite/book_story/presentation/screens/book_info/components/BookInfoStatisticSection.kt

@@ -9,6 +9,8 @@ import androidx.compose.material3.LinearProgressIndicator
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
+import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.StrokeCap
@@ -17,8 +19,7 @@ import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
 import ua.acclorite.book_story.R
 import ua.acclorite.book_story.presentation.core.components.LocalBookInfoViewModel
-import ua.acclorite.book_story.presentation.core.util.removeDigits
+import ua.acclorite.book_story.presentation.core.util.calculateProgress
-import ua.acclorite.book_story.presentation.core.util.removeTrailingZero
 
 /**
  * Statistic section.
@@ -27,13 +28,10 @@ import ua.acclorite.book_story.presentation.core.util.removeTrailingZero
 fun BookInfoStatisticSection() {
     val state = LocalBookInfoViewModel.current.state
 
-    val progress = remember(state.value.book) {
+    val progress by remember {
-        "${
+        derivedStateOf {
-            (state.value.book.progress * 100)
+            "${state.value.book.progress.calculateProgress(1)}%"
-                .toDouble()
+        }
-                .removeDigits(1)
-                .removeTrailingZero()
-        }%"
     }
     val description = stringResource(
         if (state.value.book.progress == 1f) R.string.read_done

app/src/main/java/ua/acclorite/book_story/presentation/screens/library/components/LibraryBookItem.kt

@@ -35,8 +35,7 @@ import ua.acclorite.book_story.R
 import ua.acclorite.book_story.domain.model.Book
 import ua.acclorite.book_story.domain.util.Selected
 import ua.acclorite.book_story.presentation.core.components.CustomCoverImage
-import ua.acclorite.book_story.presentation.core.util.removeDigits
+import ua.acclorite.book_story.presentation.core.util.calculateProgress
-import ua.acclorite.book_story.presentation.core.util.removeTrailingZero
 
 /**
  * Library list element item.
@@ -69,13 +68,8 @@ fun LibraryBookItem(
         else onSurfaceColor
     }
 
-    val progress = rememberSaveable(book.first) {
+    val progress = rememberSaveable(book.first.progress) {
-        "${
+        "${book.first.progress.calculateProgress(1)}%"
-            (book.first.progress * 100)
-                .toDouble()
-                .removeDigits(1)
-                .removeTrailingZero()
-        }%"
     }
 
     Column(

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/ReaderScreen.kt

@@ -128,6 +128,7 @@ fun ReaderScreenRoot(screen: Screen.Reader) {
             onEvent(
                 ReaderEvent.OnShowHideMenu(
                     fullscreenMode = mainState.value.fullscreen,
+                    saveCheckpoint = true,
                     activity = context
                 )
             )
@@ -138,6 +139,7 @@ fun ReaderScreenRoot(screen: Screen.Reader) {
             ReaderEvent.OnShowHideMenu(
                 show = state.value.showMenu,
                 fullscreenMode = mainState.value.fullscreen,
+                saveCheckpoint = false,
                 activity = context
             )
         )
@@ -201,6 +203,7 @@ private fun ReaderScreen(lazyListState: LazyListState) {
                         ReaderEvent.OnShowHideMenu(
                             show = false,
                             fullscreenMode = mainState.value.fullscreen,
+                            saveCheckpoint = false,
                             activity = context
                         )
                     )
@@ -414,6 +417,7 @@ private fun ReaderScreen(lazyListState: LazyListState) {
                                         onEvent(
                                             ReaderEvent.OnShowHideMenu(
                                                 fullscreenMode = mainState.value.fullscreen,
+                                                saveCheckpoint = true,
                                                 activity = context
                                             )
                                         )

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/components/ReaderTextParagraph.kt

@@ -110,6 +110,7 @@ fun LazyItemScope.ReaderTextParagraph(
                             onEvent(
                                 ReaderEvent.OnShowHideMenu(
                                     fullscreenMode = fullscreenMode,
+                                    saveCheckpoint = true,
                                     activity = context as ComponentActivity
                                 )
                             )

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/components/app_bar/ReaderBottomBar.kt

@@ -1,14 +1,28 @@
 package ua.acclorite.book_story.presentation.screens.reader.components.app_bar
 
+import androidx.compose.animation.expandHorizontally
+import androidx.compose.animation.fadeIn
+import androidx.compose.animation.fadeOut
+import androidx.compose.animation.shrinkHorizontally
+import androidx.compose.animation.slideInHorizontally
+import androidx.compose.animation.slideOutHorizontally
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.navigationBarsPadding
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.automirrored.filled.ArrowForward
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Slider
 import androidx.compose.material3.SliderDefaults
@@ -19,19 +33,24 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
 import androidx.compose.ui.unit.dp
+import ua.acclorite.book_story.R
+import ua.acclorite.book_story.domain.util.Direction
+import ua.acclorite.book_story.presentation.core.components.CustomAnimatedVisibility
+import ua.acclorite.book_story.presentation.core.components.CustomIconButton
 import ua.acclorite.book_story.presentation.core.components.LocalHistoryViewModel
 import ua.acclorite.book_story.presentation.core.components.LocalLibraryViewModel
 import ua.acclorite.book_story.presentation.core.components.LocalReaderViewModel
-import ua.acclorite.book_story.presentation.core.util.removeDigits
+import ua.acclorite.book_story.presentation.core.util.calculateProgress
-import ua.acclorite.book_story.presentation.core.util.removeTrailingZero
 import ua.acclorite.book_story.presentation.screens.history.data.HistoryEvent
 import ua.acclorite.book_story.presentation.screens.library.data.LibraryEvent
 import ua.acclorite.book_story.presentation.screens.reader.data.ReaderEvent
 import ua.acclorite.book_story.presentation.ui.Colors
 
 /**
- * Reader bottom bar. Has a slider to change progress.
+ * Reader bottom bar.
+ * Has a slider to change progress.
  */
 @Composable
 fun ReaderBottomBar() {
@@ -40,13 +59,26 @@ fun ReaderBottomBar() {
     val onLibraryEvent = LocalLibraryViewModel.current.onEvent
     val onHistoryEvent = LocalHistoryViewModel.current.onEvent
 
-    val progress by remember(state.value.book.progress) {
+    val progress by remember {
         derivedStateOf {
-            (state.value.book.progress * 100)
+            "${state.value.book.progress.calculateProgress(4)}%"
-                .toDouble()
+        }
-                .removeDigits(4)
+    }
-                .removeTrailingZero()
+    val arrowDirection by remember {
-                .dropWhile { it == '-' } + "%"
+        derivedStateOf {
+            val checkpoint = state.value.checkpoint.first
+            val index = state.value.listState.firstVisibleItemIndex
+
+            when {
+                checkpoint > index -> Direction.END
+                checkpoint < index -> Direction.START
+                else -> Direction.NEUTRAL
+            }
+        }
+    }
+    val checkpointProgress by remember {
+        derivedStateOf {
+            (state.value.checkpoint.first / state.value.text.lastIndex.toFloat()) * 0.987f
         }
     }
 
@@ -60,7 +92,7 @@ fun ReaderBottomBar() {
                 onClick = {}
             )
             .navigationBarsPadding()
-            .padding(horizontal = 24.dp)
+            .padding(horizontal = 18.dp)
             .padding(top = 16.dp),
         horizontalAlignment = Alignment.CenterHorizontally,
         verticalArrangement = Arrangement.Center
@@ -70,7 +102,35 @@ fun ReaderBottomBar() {
             color = MaterialTheme.colorScheme.onSurface,
             style = MaterialTheme.typography.titleLarge
         )
-        Spacer(modifier = Modifier.height(3.dp))
+        Row(
+            modifier = Modifier.padding(top = 3.dp, bottom = 5.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            CustomAnimatedVisibility(
+                visible = arrowDirection == Direction.START,
+                enter = expandHorizontally(expandFrom = Alignment.Start) + fadeIn() + slideInHorizontally { -it },
+                exit = shrinkHorizontally(shrinkTowards = Alignment.Start) + fadeOut() + slideOutHorizontally { -it }
+            ) {
+                CustomIconButton(
+                    icon = Icons.AutoMirrored.Default.ArrowBack,
+                    contentDescription = R.string.checkpoint_back_content_desc,
+                    modifier = Modifier.size(24.dp),
+                    color = MaterialTheme.colorScheme.primary,
+                    disableOnClick = false
+                ) {
+                    onEvent(
+                        ReaderEvent.OnRestoreCheckpoint { book ->
+                            onLibraryEvent(LibraryEvent.OnUpdateBook(book))
+                            onHistoryEvent(HistoryEvent.OnUpdateBook(book))
+                        }
+                    )
+                }
+            }
+
+            Box(
+                modifier = Modifier.weight(1f),
+                contentAlignment = Alignment.CenterStart
+            ) {
                 Slider(
                     value = state.value.book.progress,
                     enabled = !state.value.lockMenu,
@@ -97,6 +157,44 @@ fun ReaderBottomBar() {
                         disabledInactiveTrackColor = MaterialTheme.colorScheme.secondary.copy(0.15f),
                     )
                 )
-        Spacer(modifier = Modifier.height(5.dp))
+                if (arrowDirection != Direction.NEUTRAL) {
+                    Row(Modifier.fillMaxWidth()) {
+                        Spacer(
+                            modifier = Modifier.fillMaxWidth(checkpointProgress)
+                        )
+                        Box(
+                            Modifier
+                                .width(4.dp)
+                                .height(16.dp)
+                                .clip(RoundedCornerShape(0.5.dp))
+                                .background(
+                                    MaterialTheme.colorScheme.onPrimary.copy(0.6f)
+                                )
+                        )
+                    }
+                }
+            }
+
+            CustomAnimatedVisibility(
+                visible = arrowDirection == Direction.END,
+                enter = expandHorizontally() + fadeIn() + slideInHorizontally { it },
+                exit = shrinkHorizontally() + fadeOut() + slideOutHorizontally { it }
+            ) {
+                CustomIconButton(
+                    icon = Icons.AutoMirrored.Default.ArrowForward,
+                    contentDescription = R.string.checkpoint_forward_content_desc,
+                    modifier = Modifier.size(24.dp),
+                    color = MaterialTheme.colorScheme.primary,
+                    disableOnClick = false
+                ) {
+                    onEvent(
+                        ReaderEvent.OnRestoreCheckpoint { book ->
+                            onLibraryEvent(LibraryEvent.OnUpdateBook(book))
+                            onHistoryEvent(HistoryEvent.OnUpdateBook(book))
+                        }
+                    )
+                }
+            }
+        }
     }
 }

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/components/settings_bottom_sheet/ReaderSettingsBottomSheet.kt

@@ -63,9 +63,10 @@ fun ReaderSettingsBottomSheet() {
         )
         onEvent(
             ReaderEvent.OnShowHideMenu(
-                pagerState.currentPage != 2,
+                show = pagerState.currentPage != 2,
                 fullscreenMode = mainState.value.fullscreen,
-                context as ComponentActivity
+                saveCheckpoint = false,
+                activity = context as ComponentActivity
             )
         )
     }

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/data/ReaderEvent.kt

@@ -18,9 +18,14 @@ sealed class ReaderEvent {
     data class OnShowHideMenu(
         val show: Boolean? = null,
         val fullscreenMode: Boolean,
+        val saveCheckpoint: Boolean,
         val activity: ComponentActivity
     ) : ReaderEvent()
 
+    data class OnRestoreCheckpoint(
+        val refreshList: (Book) -> Unit
+    ) : ReaderEvent()
+
     data class OnGoBack(
         val context: ComponentActivity,
         val navigate: () -> Unit,

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/data/ReaderState.kt

@@ -16,6 +16,7 @@ data class ReaderState(
     val loading: Boolean = true,
 
     val showMenu: Boolean = false,
+    val checkpoint: Pair<Int, Int> = 0 to 0,
     val lockMenu: Boolean = false,
 
     val showSettingsBottomSheet: Boolean = false,

app/src/main/java/ua/acclorite/book_story/presentation/screens/reader/data/ReaderViewModel.kt

@@ -159,12 +159,37 @@ class ReaderViewModel @Inject constructor(
                         )
                         _state.update {
                             it.copy(
-                                showMenu = shouldShow
+                                showMenu = shouldShow,
+                                checkpoint = _state.value.listState.run {
+                                    if (!shouldShow || !event.saveCheckpoint) return@run it.checkpoint
+
+                                    firstVisibleItemIndex to firstVisibleItemScrollOffset
+                                }
                             )
                         }
                     }
                 }
 
+                is ReaderEvent.OnRestoreCheckpoint -> {
+                    launch(Dispatchers.Main) {
+                        _state.value.listState.requestScrollToItem(
+                            _state.value.checkpoint.first,
+                            _state.value.checkpoint.second
+                        )
+
+                        onEvent(
+                            ReaderEvent.OnChangeProgress(
+                                progress = calculateProgress(_state.value.checkpoint.first),
+                                firstVisibleItemIndex = _state.value.checkpoint.first,
+                                firstVisibleItemOffset = _state.value.checkpoint.second,
+                                refreshList = { book ->
+                                    event.refreshList(book)
+                                }
+                            )
+                        )
+                    }
+                }
+
                 is ReaderEvent.OnGoBack -> {
                     launch {
                         yield()
@@ -419,6 +444,7 @@ class ReaderViewModel @Inject constructor(
                     ReaderEvent.OnShowHideMenu(
                         show = false,
                         fullscreenMode = fullscreenMode,
+                        saveCheckpoint = false,
                         activity = activity
                     )
                 )

app/src/main/res/values-uk/strings.xml

@@ -594,5 +594,7 @@
     <string name="github_profile_content_desc">GitHub Профіль</string>
     <string name="drag_content_desc">Тягнути</string>
     <string name="filter_content_desc">Фільтр</string>
+    <string name="checkpoint_back_content_desc">Чекпоінт назад</string>
+    <string name="checkpoint_forward_content_desc">Чекпоінт вперед</string>
 
 </resources>

app/src/main/res/values/strings.xml

@@ -613,5 +613,7 @@
     <string name="github_profile_content_desc">GitHub Profile</string>
     <string name="drag_content_desc">Drag</string>
     <string name="filter_content_desc">Filter</string>
+    <string name="checkpoint_back_content_desc">Checkpoint back</string>
+    <string name="checkpoint_forward_content_desc">Checkpoint forward</string>
 
 </resources>