AnimateContentSize.kt

/*
 * Copyright 2025 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
 *
 *      https://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 com.alexvanyo.composelife.ui.util

import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.AnimationEndReason
import androidx.compose.animation.core.AnimationSpec
import androidx.compose.animation.core.AnimationVector2D
import androidx.compose.animation.core.FiniteAnimationSpec
import androidx.compose.animation.core.SnapSpec
import androidx.compose.animation.core.VectorConverter
import androidx.compose.animation.core.spring
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clipToBounds
import androidx.compose.ui.layout.IntrinsicMeasurable
import androidx.compose.ui.layout.IntrinsicMeasureScope
import androidx.compose.ui.layout.LayoutModifier
import androidx.compose.ui.layout.Measurable
import androidx.compose.ui.layout.MeasureResult
import androidx.compose.ui.layout.MeasureScope
import androidx.compose.ui.node.LayoutModifierNode
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.platform.InspectorInfo
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.IntSize
import androidx.compose.ui.unit.constrain
import kotlinx.coroutines.launch

/**
 * A modified version of [androidx.compose.animation.animateContentSize] that takes an [alignment] to align
 * the content while resizing.
 */
fun Modifier.animateContentSize(
    animationSpec: FiniteAnimationSpec<IntSize> = spring(),
    alignment: Alignment = Alignment.TopStart,
    finishedListener: ((initialValue: IntSize, targetValue: IntSize) -> Unit)? = null,
): Modifier =
    this.clipToBounds() then SizeAnimationModifierElement(animationSpec, alignment, finishedListener)

private data class SizeAnimationModifierElement(
    val animationSpec: FiniteAnimationSpec<IntSize>,
    val alignment: Alignment,
    val finishedListener: ((initialValue: IntSize, targetValue: IntSize) -> Unit)?,
) : ModifierNodeElement<SizeAnimationModifierNode>() {
    override fun create(): SizeAnimationModifierNode =
        SizeAnimationModifierNode(animationSpec, alignment, finishedListener)

    override fun update(node: SizeAnimationModifierNode) {
        node.animationSpec = animationSpec
        node.listener = finishedListener
    }

    override fun InspectorInfo.inspectableProperties() {
        name = "animateContentSize"
        properties["animationSpec"] = animationSpec
        properties["finishedListener"] = finishedListener
    }
}

internal val InvalidSize = IntSize(Int.MIN_VALUE, Int.MIN_VALUE)
internal val IntSize.isValid: Boolean
    get() = this != InvalidSize

/**
 * This class creates a [LayoutModifier] that measures children, and responds to children's size
 * change by animating to that size. The size reported to parents will be the animated size.
 */
private class SizeAnimationModifierNode(
    var animationSpec: AnimationSpec<IntSize>,
    val alignment: Alignment,
    var listener: ((startSize: IntSize, endSize: IntSize) -> Unit)? = null,
) : LayoutModifierNodeWithPassThroughIntrinsics() {
    private var lookaheadSize: IntSize = InvalidSize
    private var lookaheadConstraints: Constraints = Constraints()
        set(value) {
            field = value
            lookaheadConstraintsAvailable = true
        }
    private var lookaheadConstraintsAvailable: Boolean = false

    private fun targetConstraints(default: Constraints) =
        if (lookaheadConstraintsAvailable) {
            lookaheadConstraints
        } else {
            default
        }

    data class AnimData(
        val anim: Animatable<IntSize, AnimationVector2D>,
        var startSize: IntSize,
    )

    var animData: AnimData? by mutableStateOf(null)

    override fun onAttach() {
        super.onAttach()
        // When re-attached, we may be attached to a tree without lookahead scope.
        lookaheadSize = InvalidSize
        lookaheadConstraintsAvailable = false
    }

    @OptIn(ExperimentalComposeUiApi::class)
    override fun MeasureScope.measure(
        measurable: Measurable,
        constraints: Constraints,
    ): MeasureResult {
        val placeable = if (isLookingAhead) {
            lookaheadConstraints = constraints
            measurable.measure(constraints)
        } else {
            // Measure with lookahead constraints when available, to avoid unnecessary relayout
            // in child during the lookahead animation.
            measurable.measure(targetConstraints(constraints))
        }
        val measuredSize = IntSize(placeable.width, placeable.height)
        val (width, height) = if (isLookingAhead) {
            lookaheadSize = measuredSize
            measuredSize
        } else {
            animateTo(if (lookaheadSize.isValid) lookaheadSize else measuredSize).let {
                // Constrain the measure result to incoming constraints, so that parent doesn't
                // force center this layout.
                constraints.constrain(it)
            }
        }
        return layout(width, height) {
            placeable.place(
                alignment.align(
                    size = placeable.size,
                    space = IntSize(width, height),
                    layoutDirection = layoutDirection,
                ),
            )
        }
    }

    fun animateTo(targetSize: IntSize): IntSize {
        val oldData = animData
        val animSpec = animationSpec

        /**
         * True if we should perform a synchronous snap, to replace the [AnimData] entirely.
         *
         * This is only necessary if we have an old animation data, that is running or targeting a
         * different size.
         */
        val performSynchronousSnap =
            oldData != null && animSpec is SnapSpec<*> && animSpec.delay == 0 &&
                (oldData.anim.isRunning || oldData.anim.targetValue != targetSize)

        val newData = if (oldData == null || performSynchronousSnap) {
            AnimData(
                Animatable(
                    targetSize,
                    IntSize.VectorConverter,
                    IntSize(1, 1),
                ),
                targetSize,
            )
        } else {
            oldData
        }

        /**
         * If the instance of data has changed, cancel the old data to ensure it is cleaned up
         * as soon as possible.
         */
        if (oldData !== newData) {
            coroutineScope.launch {
                oldData?.anim?.stop()
            }
        }

        /**
         * On the new data, run the animation (if necessary).
         */
        newData.run {
            if (targetSize != anim.targetValue) {
                startSize = anim.value
                coroutineScope.launch {
                    val result = anim.animateTo(targetSize, animSpec)
                    if (result.endReason == AnimationEndReason.Finished) {
                        listener?.invoke(startSize, result.endState.value)
                    }
                }
            }
        }

        animData = newData
        return newData.anim.value
    }
}

internal abstract class LayoutModifierNodeWithPassThroughIntrinsics :
    LayoutModifierNode, Modifier.Node() {
    override fun IntrinsicMeasureScope.minIntrinsicWidth(
        measurable: IntrinsicMeasurable,
        height: Int,
    ) = measurable.minIntrinsicWidth(height)

    override fun IntrinsicMeasureScope.minIntrinsicHeight(
        measurable: IntrinsicMeasurable,
        width: Int,
    ) = measurable.minIntrinsicHeight(width)

    override fun IntrinsicMeasureScope.maxIntrinsicWidth(
        measurable: IntrinsicMeasurable,
        height: Int,
    ) = measurable.maxIntrinsicWidth(height)

    override fun IntrinsicMeasureScope.maxIntrinsicHeight(
        measurable: IntrinsicMeasurable,
        width: Int,
    ) = measurable.maxIntrinsicHeight(width)
}