package plus.rua.project.ui

import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.offset
import androidx.compose.foundation.layout.padding
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clipToBounds
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 androidx.compose.ui.zIndex
import kotlinx.datetime.DatePeriod
import kotlinx.datetime.LocalDate
import kotlinx.datetime.minus
import kotlinx.datetime.number
import kotlinx.datetime.plus

/**
 * 月度日历网格页面，支持折叠动画。
 *
 * 折叠时非选中行高度按 (1-p) 缩放，选中行保持原始高度，
 * 所有行通过手动 y-offset 定位，形成向选中行收缩的视觉效果。
 *
 * @param year 年份
 * @param month 月份（1-12）
 * @param selectedDate 当前选中日期
 * @param today 今天的日期，用于高亮标记
 * @param onDateClick 日期点击回调
 * @param collapseProgress 折叠进度，0f=展开，1f=折叠
 * @param rowHeightPx 从外层传入的锁定行高（像素），折叠过程中不变
 * @param effectiveWeeks 当前有效行数（含翻页插值），用于计算总高度
 * @param onRowHeightMeasured 首次行高测量回调，外层据此锁定行高
 * @param modifier 外部布局修饰符
 */
@Composable
fun CalendarMonthPage(
    year: Int,
    month: Int,
    selectedDate: LocalDate,
    today: LocalDate,
    onDateClick: (LocalDate) -> Unit,
    collapseProgress: Float,
    rowHeightPx: Int,
    effectiveWeeks: Float,
    onRowHeightMeasured: ((Int) -> Unit)? = null,
    modifier: Modifier = Modifier
) {
    val days = remember(year, month) {
        generateMonthDays(year, month)
    }
    val density = LocalDensity.current

    val weeks = days.chunked(7)
    val selectedWeekIndex = remember(weeks, selectedDate) {
        weeks.indexOfFirst { week -> week.any { it.date == selectedDate } }
    }

    val hasSelectedWeek = selectedWeekIndex >= 0
    val h = rowHeightPx.toFloat()

    // 使用与 CalendarMonthView 一致的 effectiveWeeks 计算高度，避免滑动中高度不匹配
    val totalHeightDp = if (rowHeightPx > 0) {
        val totalPx = h * (1 + (effectiveWeeks - 1) * (1f - collapseProgress))
        with(density) { totalPx.toDp() }
    } else {
        null
    }

    Box(modifier = modifier.clipToBounds().then(
        if (totalHeightDp != null) Modifier.height(totalHeightDp)
        else Modifier
    )) {
        weeks.forEachIndexed { weekIndex, week ->
            val isSelected = hasSelectedWeek && weekIndex == selectedWeekIndex
            val isAbove = hasSelectedWeek && weekIndex < selectedWeekIndex
            val isBelow = hasSelectedWeek && weekIndex > selectedWeekIndex

            val rowScale = when {
                isAbove || isBelow -> 1f - collapseProgress
                else -> 1f
            }

            val rowHeightDp = if (rowHeightPx > 0 && rowScale > 0.01f) {
                with(density) { (h * rowScale).toDp() }
            } else if (rowHeightPx <= 0) {
                null
            } else {
                0.dp
            }

            val yOffsetDp = if (rowHeightPx > 0 && hasSelectedWeek) {
                val yPx = when {
                    isAbove -> weekIndex * h * (1f - collapseProgress)
                    isSelected -> selectedWeekIndex * h * (1f - collapseProgress)
                    isBelow -> selectedWeekIndex * h * (1f - collapseProgress) + h + (weekIndex - selectedWeekIndex - 1) * h * (1f - collapseProgress)
                    else -> weekIndex * h
                }
                with(density) { yPx.toDp() }
            } else if (rowHeightPx > 0) {
                val yPx = weekIndex * h
                with(density) { yPx.toDp() }
            } else {
                0.dp
            }

            val shouldShow = rowHeightDp == null || rowHeightDp > 0.dp

            val skipDayCells = (isAbove || isBelow) && rowScale < 0.1f && collapseProgress > 0.9f

            if (shouldShow) {
                Row(
                    modifier = Modifier
                        .fillMaxWidth()
                        .zIndex(if (isSelected) 1f else 0f)
                        .then(
                            if (rowHeightDp != null) Modifier.height(rowHeightDp)
                            else Modifier
                        )
                        .offset(y = yOffsetDp)
                        .then(
                            if (weekIndex == 0 && rowHeightPx == 0) {
                                Modifier.onSizeChanged { size ->
                                    if (size.height > 0) {
                                        onRowHeightMeasured?.invoke(size.height)
                                    }
                                }
                            } else Modifier
                        )
                        .padding(vertical = ROW_PADDING_DP.dp)
                        .then(
                            if (isAbove || isBelow) Modifier.graphicsLayer { alpha = 1f - collapseProgress }
                            else Modifier
                        )
                ) {
                    if (skipDayCells) {
                        Spacer(Modifier.weight(1f))
                    } else {
                        week.forEach { dayData ->
                            DayCell(
                                date = dayData.date,
                                isCurrentMonth = dayData.isCurrentMonth,
                                isSelected = dayData.date == selectedDate,
                                isToday = dayData.date == today,
                                onClick = { onDateClick(dayData.date) },
                                modifier = Modifier.weight(1f)
                            )
                        }
                    }
                }
            }
        }
    }
}

private data class DayData(
    val date: LocalDate,
    val isCurrentMonth: Boolean
)

@Suppress("DEPRECATION") // monthNumber 无替代 API，kotlinx-datetime 尚未提供新接口
private fun generateMonthDays(year: Int, month: Int): List<DayData> {
    val firstOfMonth = LocalDate(year, month, 1)
    val offset = firstOfMonth.dayOfWeek.ordinal
    val startDate = firstOfMonth.minus(DatePeriod(days = offset))
    val nextMonth = if (month == 12) LocalDate(year + 1, 1, 1) else LocalDate(year, month + 1, 1)
    val daysInMonth = nextMonth.minus(DatePeriod(days = 1)).day
    val rows = ((offset + daysInMonth - 1) / 7) + 1
    val totalDays = rows * 7

    return (0 until totalDays).map { i ->
        val date = startDate.plus(DatePeriod(days = i))
        DayData(
            date = date,
            isCurrentMonth = date.month.number == month && date.year == year
        )
    }
}