@OptIn(ExperimentalPagerApi::class)
@Composable
fun HomeScreenToolbarContainer(
  insets: Insets,
  chanTheme: ChanTheme,
  pagerState: PagerState,
  childScreens: List<ComposeScreenWithToolbar>,
  homeScreenViewModel: HomeScreenViewModel
) {
  require(childScreens.isNotEmpty()) { "childScreens is empty!" }

  val currentPage = pagerState.currentPage.coerceIn(0, childScreens.lastIndex)
  val targetPage = pagerState.targetPage.coerceIn(0, childScreens.lastIndex)
  val animationProgress = pagerState.currentPageOffset

  val toolbarHeight = dimensionResource(id = R.dimen.toolbar_height)
  val toolbarTranslationDistancePx = with(LocalDensity.current) { toolbarHeight.toPx() / 3f }
  val toolbarTotalHeight = remember(key1 = insets.topDp) { insets.topDp + toolbarHeight }
  val transitionIsProgress = currentPage != targetPage

  val postListScrollState = homeScreenViewModel.toolbarVisibilityInfo.postListScrollState.collectAsState()
  val touchingTopOrBottomOfList by homeScreenViewModel.toolbarVisibilityInfo.postListTouchingTopOrBottomState.collectAsState()
  val isDraggingPostList by homeScreenViewModel.toolbarVisibilityInfo.postListDragState.collectAsState()
  val isDraggingFastScroller by homeScreenViewModel.toolbarVisibilityInfo.fastScrollerDragState.collectAsState()

  val toolbarAlpha by when {
    isDraggingFastScroller -> animateFloatAsState(targetValue = 0f)
    touchingTopOrBottomOfList -> animateFloatAsState(targetValue = 1f)
    isDraggingPostList -> postListScrollState
    else -> {
      val targetValue = if (postListScrollState.value > 0.5f) 1f else 0f
      animateFloatAsState(targetValue = targetValue)
    }
  }

  Column(
    modifier = Modifier
      .fillMaxWidth()
      .height(toolbarTotalHeight)
      .alpha(toolbarAlpha)
      .background(chanTheme.primaryColorCompose)
      .consumeClicks()
  ) {
    Spacer(modifier = Modifier.height(insets.topDp))

    Box(
      modifier = Modifier
        .fillMaxWidth()
        .height(toolbarHeight)
    ) {
      val zOrders = remember(key1 = childScreens.size) { IntArray(childScreens.size) { 0 } }

      for ((pageIndex, _) in childScreens.withIndex()) {
        when (pageIndex) {
          // (Currently animated) Always behind the target and above everything else
          currentPage -> zOrders[pageIndex] = 999
          // (Currently animated) Always at the top
          targetPage -> zOrders[pageIndex] = 1000
          else -> zOrders[pageIndex] = pageIndex
        }
      }

      for ((pageIndex, currentScreen) in childScreens.withIndex()) {
        val zOrder = zOrders[pageIndex]
        val screenToolbarMovable = remember(currentScreen.screenKey) {
          movableContentOf { currentScreen.Toolbar(this) }
        }

        when (pageIndex) {
          currentPage -> {
            val currentToolbarAlpha = lerpFloat(1f, 0f, Math.abs(animationProgress))
            val currentToolbarTranslation = if (animationProgress >= 0f) {
              lerpFloat(0f, toolbarTranslationDistancePx, Math.abs(animationProgress))
            } else {
              lerpFloat(0f, -toolbarTranslationDistancePx, Math.abs(animationProgress))
            }

            BuildChildToolbar(
              composeScreenWithToolbar = currentScreen,
              zOrder = zOrder,
              targetToolbarAlpha = currentToolbarAlpha,
              targetToolbarTranslation = currentToolbarTranslation,
              transitionIsProgress = transitionIsProgress,
              toolbarContent = { screenToolbarMovable() }
            )
          }
          targetPage -> {
            val targetToolbarAlpha = lerpFloat(0f, 1f, Math.abs(animationProgress))
            val targetToolbarTranslation = if (animationProgress >= 0f) {
              lerpFloat(-toolbarTranslationDistancePx, 0f, Math.abs(animationProgress))
            } else {
              lerpFloat(toolbarTranslationDistancePx, 0f, Math.abs(animationProgress))
            }

            BuildChildToolbar(
              composeScreenWithToolbar = currentScreen,
              zOrder = zOrder,
              targetToolbarAlpha = targetToolbarAlpha,
              targetToolbarTranslation = targetToolbarTranslation,
              transitionIsProgress = transitionIsProgress,
              toolbarContent = { screenToolbarMovable() }
            )
          }
          else -> {
            BuildChildToolbar(
              composeScreenWithToolbar = currentScreen,
              zOrder = zOrder,
              targetToolbarAlpha = 0f,
              targetToolbarTranslation = 0f,
              transitionIsProgress = transitionIsProgress,
              toolbarContent = { screenToolbarMovable() }
            )
          }
        }
      }
    }
  }
}

@Composable
private fun BuildChildToolbar(
  composeScreenWithToolbar: ComposeScreenWithToolbar,
  zOrder: Int,
  targetToolbarAlpha: Float,
  targetToolbarTranslation: Float,
  transitionIsProgress: Boolean,
  toolbarContent: @Composable () -> Unit
) {
  key(composeScreenWithToolbar.screenKey) {
    Box(
      modifier = Modifier
        .zIndex(zOrder.toFloat())
        .graphicsLayer {
          alpha = targetToolbarAlpha
          translationY = targetToolbarTranslation
        }
        .consumeClicks(consume = transitionIsProgress)
    ) {
      toolbarContent()
    }
  }
}