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@@ -0,0 +1,182 @@
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+package eu.kanade.presentation.components
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+
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+import androidx.compose.foundation.gestures.snapping.rememberSnapFlingBehavior
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+import androidx.compose.foundation.layout.Arrangement
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+import androidx.compose.foundation.layout.Box
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+import androidx.compose.foundation.layout.BoxScope
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+import androidx.compose.foundation.layout.PaddingValues
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+import androidx.compose.foundation.layout.wrapContentSize
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+import androidx.compose.foundation.lazy.LazyListItemInfo
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+import androidx.compose.foundation.lazy.LazyListState
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+import androidx.compose.foundation.lazy.LazyRow
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+import androidx.compose.runtime.Composable
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+import androidx.compose.runtime.LaunchedEffect
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+import androidx.compose.runtime.Stable
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+import androidx.compose.runtime.getValue
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+import androidx.compose.runtime.mutableStateOf
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+import androidx.compose.runtime.saveable.Saver
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+import androidx.compose.runtime.saveable.listSaver
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+import androidx.compose.runtime.saveable.rememberSaveable
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+import androidx.compose.runtime.setValue
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+import androidx.compose.runtime.snapshotFlow
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+import androidx.compose.ui.Alignment
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+import androidx.compose.ui.Modifier
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+import androidx.compose.ui.util.fastMaxBy
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+import kotlinx.coroutines.flow.distinctUntilChanged
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+
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+@Composable
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+fun HorizontalPager(
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+ count: Int,
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+ modifier: Modifier = Modifier,
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+ state: PagerState = rememberPagerState(),
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+ key: ((page: Int) -> Any)? = null,
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+ contentPadding: PaddingValues = PaddingValues(),
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+ verticalAlignment: Alignment.Vertical = Alignment.CenterVertically,
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+ userScrollEnabled: Boolean = true,
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+ content: @Composable BoxScope.(page: Int) -> Unit,
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+) {
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+ Pager(
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+ count = count,
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+ modifier = modifier,
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+ state = state,
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+ isVertical = false,
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+ key = key,
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+ contentPadding = contentPadding,
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+ verticalAlignment = verticalAlignment,
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+ userScrollEnabled = userScrollEnabled,
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+ content = content,
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+ )
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+}
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+
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+@Composable
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+private fun Pager(
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+ count: Int,
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+ modifier: Modifier,
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+ state: PagerState,
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+ isVertical: Boolean,
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+ key: ((page: Int) -> Any)?,
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+ contentPadding: PaddingValues,
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+ userScrollEnabled: Boolean,
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+ verticalAlignment: Alignment.Vertical = Alignment.CenterVertically,
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+ horizontalAlignment: Alignment.Horizontal = Alignment.CenterHorizontally,
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+ content: @Composable BoxScope.(page: Int) -> Unit,
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+) {
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+ LaunchedEffect(count) {
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+ state.currentPage = minOf(count - 1, state.currentPage).coerceAtLeast(0)
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+ }
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+
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+ LaunchedEffect(state) {
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+ snapshotFlow { state.mostVisiblePageLayoutInfo?.index }
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+ .distinctUntilChanged()
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+ .collect { state.updateCurrentPageBasedOnLazyListState() }
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+ }
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+
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+ if (isVertical) {
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+ LazyColumn(
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+ modifier = modifier,
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+ state = state.lazyListState,
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+ contentPadding = contentPadding,
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+ horizontalAlignment = horizontalAlignment,
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+ verticalArrangement = Arrangement.aligned(verticalAlignment),
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+ userScrollEnabled = userScrollEnabled,
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+ flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
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+ ) {
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+ items(
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+ count = count,
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+ key = key,
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+ ) { page ->
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+ Box(
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+ modifier = Modifier
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+ .fillParentMaxHeight()
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+ .wrapContentSize(),
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+ ) {
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+ content(this, page)
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+ }
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+ }
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+ }
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+ } else {
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+ LazyRow(
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+ modifier = modifier,
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+ state = state.lazyListState,
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+ contentPadding = contentPadding,
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+ verticalAlignment = verticalAlignment,
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+ horizontalArrangement = Arrangement.aligned(horizontalAlignment),
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+ userScrollEnabled = userScrollEnabled,
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+ flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
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+ ) {
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+ items(
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+ count = count,
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+ key = key,
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+ ) { page ->
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+ Box(
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+ modifier = Modifier
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+ .fillParentMaxWidth()
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+ .wrapContentSize(),
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+ ) {
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+ content(this, page)
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+ }
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+ }
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+ }
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+ }
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+}
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+
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+@Composable
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+fun rememberPagerState(
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+ initialPage: Int = 0,
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+) = rememberSaveable(saver = PagerState.Saver) {
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+ PagerState(currentPage = initialPage)
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+}
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+
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+@Stable
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+class PagerState(
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+ currentPage: Int = 0,
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+) {
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+ init { check(currentPage >= 0) { "currentPage cannot be less than zero" } }
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+
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+ val lazyListState = LazyListState(firstVisibleItemIndex = currentPage)
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+
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+ private var _currentPage by mutableStateOf(currentPage)
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+
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+ var currentPage: Int
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+ get() = _currentPage
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+ set(value) {
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+ if (value != _currentPage) {
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+ _currentPage = value
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+ }
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+ }
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+
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+ val mostVisiblePageLayoutInfo: LazyListItemInfo?
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+ get() {
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+ val layoutInfo = lazyListState.layoutInfo
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+ return layoutInfo.visibleItemsInfo.fastMaxBy {
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+ val start = maxOf(it.offset, 0)
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+ val end = minOf(
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+ it.offset + it.size,
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+ layoutInfo.viewportEndOffset - layoutInfo.afterContentPadding,
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+ )
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+ end - start
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+ }
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+ }
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+
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+ fun updateCurrentPageBasedOnLazyListState() {
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+ mostVisiblePageLayoutInfo?.let {
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+ currentPage = it.index
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+ }
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+ }
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+
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+ suspend fun animateScrollToPage(page: Int) {
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+ lazyListState.animateScrollToItem(index = page)
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+ }
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+
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+ suspend fun scrollToPage(page: Int) {
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+ lazyListState.scrollToItem(index = page)
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+ updateCurrentPageBasedOnLazyListState()
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+ }
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+
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+ companion object {
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+ val Saver: Saver<PagerState, *> = listSaver(
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+ save = { listOf(it.currentPage) },
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+ restore = { PagerState(it[0]) },
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+ )
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+ }
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+}
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Ivan Iskandar