package plus.rua.project.ui

import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.statusBarsPadding
import androidx.compose.foundation.pager.rememberPagerState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableIntStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clipToBounds
import androidx.compose.ui.graphics.TransformOrigin
import androidx.compose.ui.graphics.graphicsLayer
import androidx.compose.ui.layout.onSizeChanged
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.unit.dp
import kotlinx.datetime.DatePeriod
import kotlinx.datetime.LocalDate
import kotlinx.datetime.TimeZone
import kotlinx.datetime.number
import kotlinx.datetime.plus
import kotlinx.datetime.todayIn
import kotlinx.coroutines.launch
import plus.rua.project.CalendarViewModel
import kotlin.math.abs
import kotlin.time.Clock

/**
 * 日历主界面，包含月/周视图切换、折叠动画和年视图缩放转场。
 *
 * 折叠时日历从月视图收缩为周视图（1行），BottomCard 同步上移填充空间。
 * 点击月份标题切换年视图，以当前月为锚点缩放转场。
 *
 * @param modifier 外部布局修饰符
 */
@Composable
fun CalendarMonthView(
    modifier: Modifier = Modifier
) {
    val coroutineScope = rememberCoroutineScope()
    val viewModel = remember { CalendarViewModel(coroutineScope) }
    val today = remember { Clock.System.todayIn(TimeZone.currentSystemDefault()) }
    val currentYear by remember { derivedStateOf { viewModel.selectedDate.year } }

    @Suppress("DEPRECATION") // monthNumber 无替代 API，kotlinx-datetime 尚未提供新接口
    val currentMonth by remember { derivedStateOf { viewModel.selectedDate.month.number } }
    val density = LocalDensity.current

    var monthHeaderHeightPx by remember { mutableIntStateOf(0) }
    var weekdayHeaderHeightPx by remember { mutableIntStateOf(0) }
    var rowHeightPx by remember { mutableIntStateOf(0) }
    var screenWidthPx by remember { mutableIntStateOf(0) }
    var screenHeightPx by remember { mutableIntStateOf(0) }
    var calendarContentHeightPx by remember { mutableIntStateOf(0) }

    val pagerState = rememberPagerState(initialPage = START_PAGE, pageCount = { Int.MAX_VALUE })

    // 折叠态 WeekPager 切月时，持续同步 CalendarPager 的 pagerState
    LaunchedEffect(viewModel.selectedDate) {
        @Suppress("DEPRECATION") // monthNumber 无替代 API
        val targetPage = yearMonthToPage(
            viewModel.selectedDate.year, viewModel.selectedDate.month.number,
            today.year, today.month.number
        )
        if (targetPage != pagerState.currentPage) {
            pagerState.scrollToPage(targetPage)
        }
    }

    val collapseProgress = viewModel.collapseProgress
    val yearProgress = viewModel.yearViewProgress
    val headerHeightPx = monthHeaderHeightPx + weekdayHeaderHeightPx
    val rowPaddingPx = with(density) { ROW_PADDING_DP.dp.toPx() }.toInt()
    val cardGapPx = with(density) {
        lerp(
            CARD_GAP_EXPANDED_DP.toFloat(),
            CARD_GAP_COLLAPSED_DP.toFloat(),
            collapseProgress
        ).dp.toPx()
    }.toInt()

    val interpolatedWeeks by remember {
        derivedStateOf {
            val fraction = pagerState.currentPageOffsetFraction
            if (abs(fraction) > OFFSET_FRACTION_THRESHOLD) {
                val cp = pagerState.currentPage
                val baseWeeks = calculateWeeksCountForPage(cp, today)
                val targetPage = cp + if (fraction > 0) 1 else -1
                val targetWeeks = calculateWeeksCountForPage(targetPage, today)
                lerp(baseWeeks.toFloat(), targetWeeks.toFloat(), abs(fraction))
            } else {
                calculateWeeksCountForPage(pagerState.currentPage, today).toFloat()
            }
        }
    }

    val estimatedRowHeightPx = if (screenWidthPx > 0) {
        val cellWidth =
            (screenWidthPx - with(density) { (HORIZONTAL_PADDING_DP * 2).dp.toPx() }) / 7
        val rowPadding = with(density) { (ROW_PADDING_DP * 2).dp.toPx() }
        (cellWidth + rowPadding).toInt()
    } else 0

    val effectiveRowHeightPx = if (rowHeightPx > 0) rowHeightPx else estimatedRowHeightPx
    val effectiveWeeks = interpolatedWeeks

    val gridHeightPx = if (effectiveRowHeightPx > 0) {
        val rowH = effectiveRowHeightPx.toFloat()
        if (collapseProgress > OFFSET_FRACTION_THRESHOLD) {
            (rowH * (1 + (effectiveWeeks - 1) * (1f - collapseProgress))).toInt()
        } else {
            (rowH * effectiveWeeks).toInt()
        }
    } else 0

    val calendarAreaHeightPx = headerHeightPx + gridHeightPx + rowPaddingPx + cardGapPx
    val cardHeightPx =
        if (screenHeightPx > 0 && calendarAreaHeightPx > 0) screenHeightPx - calendarAreaHeightPx else 0

    val pagerModifier = if (rowHeightPx > 0 && gridHeightPx > 0) {
        Modifier
            .height(with(density) { gridHeightPx.toDp() })
            .clipToBounds()
    } else {
        Modifier
    }

    // 年视图锚点缩放：当前月在 4×3 网格中的归一化位置
    val anchorPivotX = ((currentMonth - 1) % 3 + 0.5f) / 3f
    val anchorPivotY = ((currentMonth - 1) / 3 + 0.5f) / 4f

    // 月视图层缩放：从 1f 缩小到 ~0.3f（年网格单格 vs 月视图大小比）
    val monthScale = 1f - yearProgress * 0.7f
    val monthAlpha = (1f - yearProgress * 1.4f).coerceIn(0f, 1f)

    // 年视图层缩放：从 ~3.3f 放大到 1f
    val yearScale = lerp(3.3f, 1f, yearProgress)
    val yearAlpha = ((yearProgress - 0.2f) / 0.8f).coerceIn(0f, 1f)

    Box(
        modifier = modifier
            .fillMaxSize()
            .statusBarsPadding()
            .onSizeChanged { size ->
                screenWidthPx = size.width
                screenHeightPx = size.height
            }
    ) {
        // 月视图层
        Column(
            modifier = Modifier
                .fillMaxSize()
                .graphicsLayer {
                    scaleX = monthScale
                    scaleY = monthScale
                    alpha = monthAlpha
                    transformOrigin = TransformOrigin(anchorPivotX, anchorPivotY)
                }
                .padding(horizontal = HORIZONTAL_PADDING_DP.dp)
        ) {
            MonthHeader(
                year = currentYear,
                month = currentMonth,
                weekNumber = viewModel.getIsoWeekNumber(viewModel.selectedDate),
                showToday = viewModel.selectedDate != today,
                onToggleYearView = { viewModel.toggleYearView() },
                onToday = {
                    viewModel.selectDate(today)
                    @Suppress("DEPRECATION") // monthNumber 无替代 API
                    val targetPage = yearMonthToPage(
                        today.year, today.month.number,
                        today.year, today.month.number
                    )
                    if (targetPage != pagerState.currentPage) {
                        coroutineScope.launch { pagerState.animateScrollToPage(targetPage) }
                    }
                },
                modifier = Modifier.onSizeChanged { size ->
                    monthHeaderHeightPx = size.height
                }
            )
            WeekdayHeader(
                modifier = Modifier.fillMaxWidth().padding(bottom = ROW_PADDING_DP.dp)
                    .onSizeChanged { size ->
                        weekdayHeaderHeightPx = size.height
                    }
            )
            if (viewModel.isCollapsed && viewModel.collapseProgress >= 1f) {
                WeekPager(
                    selectedDate = viewModel.selectedDate,
                    today = today,
                    onDateClick = { date -> viewModel.selectDate(date) },
                    onWeekChanged = { weekMonday ->
                        val weekSunday = weekMonday.plus(DatePeriod(days = 6))
                        val date = when {
                            today in weekMonday..weekSunday -> today
                            weekMonday.month != weekSunday.month -> {
                                if (weekMonday < viewModel.selectedDate) {
                                    @Suppress("DEPRECATION") // monthNumber 无替代 API
                                    LocalDate(weekSunday.year, weekSunday.month.number, 1)
                                } else {
                                    weekMonday
                                }
                            }
                            else -> weekMonday
                        }
                        viewModel.selectDate(date)
                    },
                    modifier = pagerModifier
                )
            } else {
                CalendarPager(
                    selectedDate = viewModel.selectedDate,
                    today = today,
                    onDateClick = { date -> viewModel.selectDate(date) },
                    onMonthChanged = { year, month ->
                        @Suppress("DEPRECATION") // monthNumber 无替代 API
                        val date = if (year == today.year && today.month.number == month) today
                        else LocalDate(year, month, 1)
                        viewModel.selectDate(date)
                    },
                    collapseProgress = viewModel.collapseProgress,
                    rowHeightPx = rowHeightPx,
                    effectiveWeeks = effectiveWeeks,
                    onRowHeightMeasured = { h ->
                        if (h > 0) rowHeightPx = h
                    },
                    pagerState = pagerState,
                    modifier = pagerModifier
                )
            }
        }

        // 年视图层
        if (viewModel.isYearView || yearProgress > 0.01f) {
            YearGridView(
                year = viewModel.yearViewYear,
                selectedMonth = if (viewModel.yearViewYear == currentYear) currentMonth else 0,
                today = today,
                onMonthClick = { month ->
                    viewModel.selectMonthFromYearView(month)
                    // 同步 CalendarPager 到目标月份
                    @Suppress("DEPRECATION") // monthNumber 无替代 API
                    val targetPage = yearMonthToPage(
                        viewModel.yearViewYear, month,
                        today.year, today.month.number
                    )
                    if (targetPage != pagerState.currentPage) {
                        coroutineScope.launch { pagerState.scrollToPage(targetPage) }
                    }
                },
                onYearChange = { newYear ->
                    if (newYear > viewModel.yearViewYear) viewModel.incrementYear()
                    else viewModel.decrementYear()
                },
                modifier = Modifier
                    .fillMaxSize()
                    .graphicsLayer {
                        scaleX = yearScale
                        scaleY = yearScale
                        alpha = yearAlpha
                        transformOrigin = TransformOrigin(anchorPivotX, anchorPivotY)
                    }
                    .padding(horizontal = HORIZONTAL_PADDING_DP.dp)
            )
        }

        // BottomCard：年视图时隐藏
        if (yearProgress < 0.01f) {
            val dragRangeMinPx = with(density) { DRAG_RANGE_MIN_DP.dp.toPx() }
            val dragRangePx = if (effectiveRowHeightPx > 0) {
                maxOf((effectiveWeeks - 1) * effectiveRowHeightPx.toFloat(), dragRangeMinPx)
            } else {
                dragRangeMinPx
            }

            if (cardHeightPx > 0) {
                BottomCard(
                    viewModel = viewModel,
                    dragRangePx = dragRangePx,
                    modifier = Modifier
                        .fillMaxWidth()
                        .height(with(density) { cardHeightPx.toDp() })
                        .align(Alignment.BottomCenter)
                )
            }
        }
    }
}