compose/foundation/foundation/integration-tests/foundation-demos/src/main/java/androidx/compose/foundation/demos/snapping/RowSnappingDemos.kt

/*
 * Copyright 2022 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package androidx.compose.foundation.demos.snapping

import androidx.compose.animation.core.DecayAnimationSpec
import androidx.compose.animation.rememberSplineBasedDecay
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.ScrollState
import androidx.compose.foundation.background
import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.snapping.SnapLayoutInfoProvider
import androidx.compose.foundation.gestures.snapping.rememberSnapFlingBehavior
import androidx.compose.foundation.horizontalScroll
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxHeight
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.width
import androidx.compose.foundation.rememberScrollState
import androidx.compose.integration.demos.common.ComposableDemo
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.drawWithContent
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.layout.onSizeChanged
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.unit.IntSize
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp

val RowSnappingDemos = listOf(
    ComposableDemo("Single Item - Same Size Items") { SinglePageSnapping() },
    ComposableDemo("Multi Item - Decayed Snapping") { DecayedSnappingDemo() },
    ComposableDemo("Multi Item - View Port Based Offset") { ViewPortBasedSnappingDemo() },
)

/**
 * Snapping happens to the next item and items have the same size
 */
@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun SinglePageSnapping() {
    val scrollState = rememberScrollState()
    val layoutSizeState = remember { mutableStateOf(IntSize.Zero) }
    val layoutInfoProvider = rememberNextItemSnappingLayoutInfoProvider(scrollState) {
        layoutSizeState.value.width.toFloat()
    }
    val snapFlingBehavior = rememberSnapFlingBehavior(snapLayoutInfoProvider = layoutInfoProvider)
    RowSnappingMainLayout(snapFlingBehavior, scrollState) { layoutSizeState.value = it }
}

/**
 * Snapping happens after a decay animation. Items have the same size.
 */
@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun DecayedSnappingDemo() {
    val scrollState = rememberScrollState()
    val layoutSizeState = remember { mutableStateOf(IntSize.Zero) }
    val layoutInfoProvider = rememberRowSnapLayoutInfoProvider(scrollState) {
        layoutSizeState.value.width.toFloat()
    }
    val snapFlingBehavior = rememberSnapFlingBehavior(snapLayoutInfoProvider = layoutInfoProvider)
    RowSnappingMainLayout(snapFlingBehavior, scrollState) { layoutSizeState.value = it }
}

/**
 * Snapping happens to at max one view port item's worth distance.
 */
@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun ViewPortBasedSnappingDemo() {
    val scrollState = rememberScrollState()
    val layoutSizeState = remember { mutableStateOf(IntSize.Zero) }
    val layoutInfoProvider = rememberViewPortSnapLayoutInfoProvider(scrollState) {
        layoutSizeState.value.width.toFloat()
    }
    val snapFlingBehavior = rememberSnapFlingBehavior(snapLayoutInfoProvider = layoutInfoProvider)
    RowSnappingMainLayout(snapFlingBehavior, scrollState) { layoutSizeState.value = it }
}

@Composable
private fun RowSnappingMainLayout(
    snapFlingBehavior: FlingBehavior,
    scrollState: ScrollState,
    onLayoutSizeChanged: (IntSize) -> Unit
) {
    Box(
        modifier = Modifier
            .fillMaxSize()
            .drawWithContent {
                drawContent()
                drawAnchor(CenterAnchor)
            }, contentAlignment = Alignment.Center
    ) {
        Row(
            modifier = Modifier
                .fillMaxWidth()
                .onSizeChanged(onLayoutSizeChanged)
                .fillMaxHeight(0.7f)
                .horizontalScroll(scrollState, flingBehavior = snapFlingBehavior)
        ) {
            repeat(100) {
                RowSnappingItem(position = it)
            }
        }
    }
}

@Composable
private fun RowSnappingItem(position: Int) {
    Box(
        modifier = Modifier
            .fillMaxHeight()
            .width(RowItemSize)
            .padding(4.dp)
            .background(Color.Gray)
            .drawWithContent {
                drawContent()
                drawAnchor(CenterAnchor)
            },
        contentAlignment = Alignment.Center
    ) {
        Text(text = position.toString(), fontSize = 40.sp)
    }
}

@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun rememberRowSnapLayoutInfoProvider(
    scrollState: ScrollState,
    layoutSize: () -> Float
): SnapLayoutInfoProvider {
    val density = LocalDensity.current
    return remember(scrollState, layoutSize) {
        SnapLayoutInfoProvider(
            scrollState = scrollState,
            itemSize = { with(density) { RowItemSize.toPx() } },
            layoutSize = layoutSize
        )
    }
}

@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun rememberNextItemSnappingLayoutInfoProvider(
    scrollState: ScrollState,
    layoutSize: () -> Float
): SnapLayoutInfoProvider {
    val density = LocalDensity.current
    val basedSnappingLayoutInfoProvider = SnapLayoutInfoProvider(
        scrollState = scrollState,
        itemSize = { with(density) { RowItemSize.toPx() } },
        layoutSize = layoutSize
    )
    return remember(scrollState, layoutSize) {
        object : SnapLayoutInfoProvider by basedSnappingLayoutInfoProvider {
            override fun calculateApproachOffset(initialVelocity: Float): Float {
                return 0f
            }
        }
    }
}

@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun rememberViewPortSnapLayoutInfoProvider(
    scrollState: ScrollState,
    layoutSize: () -> Float
): SnapLayoutInfoProvider {
    val density = LocalDensity.current
    val decayAnimationSpec: DecayAnimationSpec<Float> = rememberSplineBasedDecay()
    val baseSnapLayoutInfoProvider = rememberScrollStateLayoutInfoProvider(
        scrollState = scrollState,
        layoutSize = layoutSize
    )

    return remember(baseSnapLayoutInfoProvider, density, layoutSize) {
        ViewPortBasedSnappingLayoutInfoProvider(
            baseSnapLayoutInfoProvider,
            decayAnimationSpec,
            viewPortStep = layoutSize,
            itemSize = { with(density) { RowItemSize.toPx() } }
        )
    }
}

@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun rememberScrollStateLayoutInfoProvider(
    scrollState: ScrollState,
    layoutSize: () -> Float
): SnapLayoutInfoProvider {
    val density = LocalDensity.current
    return remember(scrollState, layoutSize, density) {
        SnapLayoutInfoProvider(
            scrollState = scrollState,
            itemSize = { with(density) { RowItemSize.toPx() } },
            layoutSize = layoutSize
        )
    }
}

private val RowItemSize = 250.dp