val visible = remember { mutableStateOf(true) }
AnimatedVisibility(visible = visible.value,) {
    Text(text = "天青色等煙雨，而我在等你，炊煙裊裊升起，隔江千萬(wàn)里")
}

@Composable
fun AnimatedVisibility(
    visible: Boolean,
    modifier: Modifier = Modifier,
    enter: EnterTransition = fadeIn() + expandIn(),
    exit: ExitTransition = shrinkOut() + fadeOut(),
    label: String = "AnimatedVisibility",
    content: @Composable() AnimatedVisibilityScope.() -> Unit
) {
    val transition = updateTransition(visible, label)
    AnimatedEnterExitImpl(transition, { it }, modifier, enter, exit, content)
}

@Immutable
sealed class EnterTransition {
    internal abstract val data: TransitionData
    // 組合不同的進(jìn)入轉(zhuǎn)換。組合的順序并不重要，因?yàn)檫@些將同時(shí)啟動(dòng)
    @Stable
    operator fun plus(enter: EnterTransition): EnterTransition {
        return EnterTransitionImpl(
            TransitionData(
                fade = data.fade ?: enter.data.fade,
                slide = data.slide ?: enter.data.slide,
                changeSize = data.changeSize ?: enter.data.changeSize,
                scale = data.scale ?: enter.data.scale
            )
        )
    }
    companion object {
        // 當(dāng)不需要輸入轉(zhuǎn)換時(shí)，可以使用此函數(shù)。
        val None: EnterTransition = EnterTransitionImpl(TransitionData())
    }
}

@Immutable
private class EnterTransitionImpl(override val data: TransitionData) : EnterTransition()

@Immutable
internal data class TransitionData(
    val fade: Fade? = null,
    val slide: Slide? = null,
    val changeSize: ChangeSize? = null,
    val scale: Scale? = null
)

@Immutable
internal data class Fade(val alpha: Float, val animationSpec: FiniteAnimationSpec<Float>)
@Immutable
internal data class Slide(
    val slideOffset: (fullSize: IntSize) -> IntOffset,
    val animationSpec: FiniteAnimationSpec<IntOffset>
)
@Immutable
internal data class ChangeSize(
    val alignment: Alignment,
    val size: (fullSize: IntSize) -> IntSize = { IntSize(0, 0) },
    val animationSpec: FiniteAnimationSpec<IntSize>,
    val clip: Boolean = true
)
@Immutable
internal data class Scale(
    val scale: Float,
    val transformOrigin: TransformOrigin,
    val animationSpec: FiniteAnimationSpec<Float>
)

interface FiniteAnimationSpec<T> : AnimationSpec<T> {
    override fun <V : AnimationVector> vectorize(
        converter: TwoWayConverter<T, V>
    ): VectorizedFiniteAnimationSpec<V>
}

@Immutable
sealed class ExitTransition {
    internal abstract val data: TransitionData
    // 結(jié)合不同的退出轉(zhuǎn)換，組合順序并不重要
    @Stable
    operator fun plus(exit: ExitTransition): ExitTransition {
        return ExitTransitionImpl(
            TransitionData(
                fade = data.fade ?: exit.data.fade,
                slide = data.slide ?: exit.data.slide,
                changeSize = data.changeSize ?: exit.data.changeSize,
                scale = data.scale ?: exit.data.scale
            )
        )
    }
    companion object {
        // 當(dāng)不需要內(nèi)置動(dòng)畫(huà)時(shí)使用
        val None: ExitTransition = ExitTransitionImpl(TransitionData())
    }
}

@Immutable
private class ExitTransitionImpl(override val data: TransitionData) : ExitTransition()

val transition = updateTransition(visible, label)
AnimatedEnterExitImpl(transition, { it }, modifier, enter, exit, content)

@Composable
fun <T> updateTransition(
    targetState: T,
    label: String? = null
): Transition<T> {
    val transition = remember { Transition(targetState, label = label) }
    transition.animateTo(targetState)
    DisposableEffect(transition) {
        onDispose {
            // 出去的時(shí)候清理干凈，確保觀察者不會(huì)被困在中間狀態(tài)
            transition.onTransitionEnd()
        }
    }
    return transition
}

@Stable
class Transition<S> @PublishedApi internal constructor(
    private val transitionState: MutableTransitionState<S>,
    val label: String? = null
)

internal constructor(
    initialState: S,
    label: String?
) : this(MutableTransitionState(initialState), label)

class MutableTransitionState<S>(initialState: S) {
    // 當(dāng)前的狀態(tài)
    var currentState: S by mutableStateOf(initialState)
        internal set
    // 過(guò)渡的目標(biāo)狀態(tài)
    var targetState: S by mutableStateOf(initialState)
    // 是否空閑
    val isIdle: Boolean
        get() = (currentState == targetState) && !isRunning
    // 是否運(yùn)行
    internal var isRunning: Boolean by mutableStateOf(false)
}

AnimatedEnterExitImpl(transition, { it }, modifier, enter, exit, content)

@Composable
private fun <T> AnimatedEnterExitImpl(
    transition: Transition<T>,visible: (T) -> Boolean,
    modifier: Modifier,enter: EnterTransition,
    exit: ExitTransition,content: @Composable() AnimatedVisibilityScope.() -> Unit
) {
    val isAnimationVisible = remember(transition) {
        mutableStateOf(visible(transition.currentState))
    }
    if (visible(transition.targetState) || isAnimationVisible.value || transition.isSeeking) {
        val childTransition = transition.createChildTransition(label = "EnterExitTransition") {
            transition.targetEnterExit(visible, it)
        }
        LaunchedEffect(childTransition) {
            snapshotFlow {
                childTransition.currentState == EnterExitState.Visible ||
                    childTransition.targetState == EnterExitState.Visible
            }.collect {
                isAnimationVisible.value = it
            }
        }
        AnimatedEnterExitImpl(childTransition,modifier,
            enter = enter,exit = exit,content = content
        )
    }
}

@Composable
inline fun <S, T> Transition<S>.createChildTransition(
    label: String = "ChildTransition",
    transformToChildState: @Composable (parentState: S) -> T,
): Transition<T> {
    val initialParentState = remember(this) { this.currentState }
    val initialState = transformToChildState(if (isSeeking) currentState else initialParentState)
    val targetState = transformToChildState(this.targetState)
    return createChildTransitionInternal(initialState, targetState, label)
}

@Composable
internal fun <S, T> Transition<S>.createChildTransitionInternal(
    initialState: T,
    targetState: T,
    childLabel: String,
): Transition<T> {
    val transition = remember(this) {
        Transition(MutableTransitionState(initialState), "${this.label} > $childLabel")
    }
    DisposableEffect(transition) {
        addTransition(transition)
        onDispose {
            removeTransition(transition)
        }
    }
    if (isSeeking) {
        transition.setPlaytimeAfterInitialAndTargetStateEstablished(
            initialState,
            targetState,
            this.lastSeekedTimeNanos
        )
    } else {
        transition.updateTarget(targetState)
        transition.isSeeking = false
    }
    return transition
}

@Composable
private fun <T> Transition<T>.targetEnterExit(
    visible: (T) -> Boolean,
    targetState: T
): EnterExitState = key(this) {
    if (this.isSeeking) {
        if (visible(targetState)) {
            Visible
        } else {
            if (visible(this.currentState)) {
                PostExit
            } else {
                PreEnter
            }
        }
    } else {
        val hasBeenVisible = remember { mutableStateOf(false) }
        if (visible(currentState)) {
            hasBeenVisible.value = true
        }
        if (visible(targetState)) {
            EnterExitState.Visible
        } else {
            // If never been visible, visible = false means PreEnter, otherwise PostExit
            if (hasBeenVisible.value) {
                EnterExitState.PostExit
            } else {
                EnterExitState.PreEnter
            }
        }
    }
}

enum class EnterExitState {
    // 自定義進(jìn)入動(dòng)畫(huà)的初始狀態(tài)。
    PreEnter,
    // 自定義進(jìn)入動(dòng)畫(huà)的目標(biāo)狀態(tài)，也是動(dòng)畫(huà)過(guò)程中自定義退出動(dòng)畫(huà)的初始狀態(tài)。
    Visible,
    // 自定義退出動(dòng)畫(huà)的目標(biāo)狀態(tài)。
    PostExit
}

LaunchedEffect(childTransition) {
            snapshotFlow {
                childTransition.currentState == EnterExitState.Visible ||
                    childTransition.targetState == EnterExitState.Visible
            }.collect {
                isAnimationVisible.value = it
            }
        }
AnimatedEnterExitImpl(childTransition,modifier,
            enter = enter,exit = exit,content = content
        )

@Composable
private inline fun AnimatedEnterExitImpl(
    transition: Transition<EnterExitState>,
    modifier: Modifier,
    enter: EnterTransition,
    exit: ExitTransition,
    content: @Composable AnimatedVisibilityScope.() -> Unit
) {
    if (transition.currentState == EnterExitState.Visible ||
        transition.targetState == EnterExitState.Visible
    ) {
        val scope = remember(transition) { AnimatedVisibilityScopeImpl(transition) }
        Layout(
            content = { scope.content() },
            modifier = modifier.then(transition.createModifier(enter, exit, "Built-in")),
            measurePolicy = remember { AnimatedEnterExitMeasurePolicy(scope) }
        )
    }
}

@Composable
internal fun Transition<EnterExitState>.createModifier(
    enter: EnterTransition,
    exit: ExitTransition,
    label: String
): Modifier

var modifier: Modifier = Modifier
modifier = modifier.slideInOut(
    this,
    rememberUpdatedState(enter.data.slide),
    rememberUpdatedState(exit.data.slide),
    label
).shrinkExpand(
    this,
    rememberUpdatedState(enter.data.changeSize),
    rememberUpdatedState(exit.data.changeSize),
    label
)

var shouldAnimateAlpha by remember(this) { mutableStateOf(false) }
var shouldAnimateScale by remember(this) { mutableStateOf(false) }
if (currentState == targetState && !isSeeking) {
    shouldAnimateAlpha = false
    shouldAnimateScale = false
} else {
    if (enter.data.fade != null || exit.data.fade != null) {
        shouldAnimateAlpha = true
    }
    if (enter.data.scale != null || exit.data.scale != null) {
        shouldAnimateScale = true
    }
}

if (shouldAnimateScale) {
    ......
    modifier = modifier.graphicsLayer {
        this.alpha = alpha
        this.scaleX = scale
        this.scaleY = scale
        this.transformOrigin = transformOrigin
    }
} else if (shouldAnimateAlpha) {
    modifier = modifier.graphicsLayer {
        this.alpha = alpha
    }
}

@Composable
fun RowScope.AnimatedVisibility(
    visible: Boolean,
    modifier: Modifier = Modifier,
    enter: EnterTransition = fadeIn() + expandHorizontally(),
    exit: ExitTransition = fadeOut() + shrinkHorizontally(),
    label: String = "AnimatedVisibility",
    content: @Composable() AnimatedVisibilityScope.() -> Unit
) {
    val transition = updateTransition(visible, label)
    AnimatedEnterExitImpl(transition, { it }, modifier, enter, exit, content)
}
@Composable
fun ColumnScope.AnimatedVisibility(
    visible: Boolean,
    modifier: Modifier = Modifier,
    enter: EnterTransition = fadeIn() + expandVertically(),
    exit: ExitTransition = fadeOut() + shrinkVertically(),
    label: String = "AnimatedVisibility",
    content: @Composable AnimatedVisibilityScope.() -> Unit
) {
    val transition = updateTransition(visible, label)
    AnimatedEnterExitImpl(transition, { it }, modifier, enter, exit, content)
}

@Composable
fun AnimatedVisibility(
    visibleState: MutableTransitionState<Boolean>,
    modifier: Modifier = Modifier,
    enter: EnterTransition = fadeIn() + expandIn(),
    exit: ExitTransition = fadeOut() + shrinkOut(),
    label: String = "AnimatedVisibility",
    content: @Composable() AnimatedVisibilityScope.() -> Unit
) {
    val transition = updateTransition(visibleState, label)
    AnimatedEnterExitImpl(transition, { it }, modifier, enter, exit, content)
}