tachiyomi/app/src/main/java/eu/kanade/presentation/util/Scrollbar.kt

package eu.kanade.presentation.util

/*
 * MIT License
 *
 * Copyright (c) 2022 Albert Chang
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/**
 * Code taken from https://gist.github.com/mxalbert1996/33a360fcab2105a31e5355af98216f5a
 * with some modifications to handle contentPadding.
 *
 * Modifiers for regular scrollable list is omitted.
 */

import android.view.ViewConfiguration
import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.tween
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.foundation.lazy.LazyRow
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.draw.CacheDrawScope
import androidx.compose.ui.draw.DrawResult
import androidx.compose.ui.draw.drawWithCache
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.geometry.Size
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.drawscope.DrawScope
import androidx.compose.ui.input.nestedscroll.NestedScrollConnection
import androidx.compose.ui.input.nestedscroll.NestedScrollSource
import androidx.compose.ui.input.nestedscroll.nestedScroll
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.platform.LocalLayoutDirection
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.LayoutDirection
import androidx.compose.ui.unit.dp
import androidx.compose.ui.util.fastSumBy
import kotlinx.coroutines.channels.BufferOverflow
import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.flow.collectLatest

fun Modifier.drawHorizontalScrollbar(
    state: LazyListState,
    reverseScrolling: Boolean = false,
    // The amount of offset the scrollbar position towards the top of the layout
    positionOffsetPx: Float = 0f,
): Modifier = drawScrollbar(state, Orientation.Horizontal, reverseScrolling, positionOffsetPx)

fun Modifier.drawVerticalScrollbar(
    state: LazyListState,
    reverseScrolling: Boolean = false,
    // The amount of offset the scrollbar position towards the start of the layout
    positionOffsetPx: Float = 0f,
): Modifier = drawScrollbar(state, Orientation.Vertical, reverseScrolling, positionOffsetPx)

private fun Modifier.drawScrollbar(
    state: LazyListState,
    orientation: Orientation,
    reverseScrolling: Boolean,
    positionOffset: Float,
): Modifier = drawScrollbar(
    orientation,
    reverseScrolling,
) { reverseDirection, atEnd, thickness, color, alpha ->
    val layoutInfo = state.layoutInfo
    val viewportSize = if (orientation == Orientation.Horizontal) {
        layoutInfo.viewportSize.width
    } else {
        layoutInfo.viewportSize.height
    } - layoutInfo.beforeContentPadding - layoutInfo.afterContentPadding
    val items = layoutInfo.visibleItemsInfo
    val itemsSize = items.fastSumBy { it.size }
    val showScrollbar = items.size < layoutInfo.totalItemsCount || itemsSize > viewportSize
    val estimatedItemSize = if (items.isEmpty()) 0f else itemsSize.toFloat() / items.size
    val totalSize = estimatedItemSize * layoutInfo.totalItemsCount
    val thumbSize = viewportSize / totalSize * viewportSize
    val startOffset = if (items.isEmpty()) {
        0f
    } else {
        items
            .first()
            .run {
                val startPadding = if (reverseDirection) layoutInfo.afterContentPadding else layoutInfo.beforeContentPadding
                startPadding + ((estimatedItemSize * index - offset) / totalSize * viewportSize)
            }
    }
    val drawScrollbar = onDrawScrollbar(
        orientation, reverseDirection, atEnd, showScrollbar,
        thickness, color, alpha, thumbSize, startOffset, positionOffset,
    )
    onDrawWithContent {
        drawContent()
        drawScrollbar()
    }
}

private fun CacheDrawScope.onDrawScrollbar(
    orientation: Orientation,
    reverseDirection: Boolean,
    atEnd: Boolean,
    showScrollbar: Boolean,
    thickness: Float,
    color: Color,
    alpha: () -> Float,
    thumbSize: Float,
    scrollOffset: Float,
    positionOffset: Float,
): DrawScope.() -> Unit {
    val topLeft = if (orientation == Orientation.Horizontal) {
        Offset(
            if (reverseDirection) size.width - scrollOffset - thumbSize else scrollOffset,
            if (atEnd) size.height - positionOffset - thickness else positionOffset,
        )
    } else {
        Offset(
            if (atEnd) size.width - positionOffset - thickness else positionOffset,
            if (reverseDirection) size.height - scrollOffset - thumbSize else scrollOffset,
        )
    }
    val size = if (orientation == Orientation.Horizontal) {
        Size(thumbSize, thickness)
    } else {
        Size(thickness, thumbSize)
    }

    return {
        if (showScrollbar) {
            drawRect(
                color = color,
                topLeft = topLeft,
                size = size,
                alpha = alpha(),
            )
        }
    }
}

private fun Modifier.drawScrollbar(
    orientation: Orientation,
    reverseScrolling: Boolean,
    onBuildDrawCache: CacheDrawScope.(
        reverseDirection: Boolean,
        atEnd: Boolean,
        thickness: Float,
        color: Color,
        alpha: () -> Float,
    ) -> DrawResult,
): Modifier = composed {
    val scrolled = remember {
        MutableSharedFlow<Unit>(
            extraBufferCapacity = 1,
            onBufferOverflow = BufferOverflow.DROP_OLDEST,
        )
    }
    val nestedScrollConnection = remember(orientation, scrolled) {
        object : NestedScrollConnection {
            override fun onPostScroll(
                consumed: Offset,
                available: Offset,
                source: NestedScrollSource,
            ): Offset {
                val delta = if (orientation == Orientation.Horizontal) consumed.x else consumed.y
                if (delta != 0f) scrolled.tryEmit(Unit)
                return Offset.Zero
            }
        }
    }

    val alpha = remember { Animatable(0f) }
    LaunchedEffect(scrolled, alpha) {
        scrolled.collectLatest {
            alpha.snapTo(1f)
            alpha.animateTo(0f, animationSpec = FadeOutAnimationSpec)
        }
    }

    val isLtr = LocalLayoutDirection.current == LayoutDirection.Ltr
    val reverseDirection = if (orientation == Orientation.Horizontal) {
        if (isLtr) reverseScrolling else !reverseScrolling
    } else {
        reverseScrolling
    }
    val atEnd = if (orientation == Orientation.Vertical) isLtr else true

    val context = LocalContext.current
    val thickness = remember { ViewConfiguration.get(context).scaledScrollBarSize.toFloat() }
    val color = MaterialTheme.colorScheme.onSurface.copy(alpha = 0.364f)
    Modifier
        .nestedScroll(nestedScrollConnection)
        .drawWithCache {
            onBuildDrawCache(reverseDirection, atEnd, thickness, color, alpha::value)
        }
}

private val FadeOutAnimationSpec = tween<Float>(
    durationMillis = ViewConfiguration.getScrollBarFadeDuration(),
    delayMillis = ViewConfiguration.getScrollDefaultDelay(),
)

@Preview(widthDp = 400, heightDp = 400, showBackground = true)
@Composable
fun LazyListScrollbarPreview() {
    val state = rememberLazyListState()
    LazyColumn(
        modifier = Modifier.drawVerticalScrollbar(state),
        state = state,
    ) {
        items(50) {
            Text(
                text = "Item ${it + 1}",
                modifier = Modifier
                    .fillMaxWidth()
                    .padding(16.dp),
            )
        }
    }
}

@Preview(widthDp = 400, showBackground = true)
@Composable
fun LazyListHorizontalScrollbarPreview() {
    val state = rememberLazyListState()
    LazyRow(
        modifier = Modifier.drawHorizontalScrollbar(state),
        state = state,
    ) {
        items(50) {
            Text(
                text = (it + 1).toString(),
                modifier = Modifier
                    .padding(horizontal = 8.dp, vertical = 16.dp),
            )
        }
    }
}