package plus.rua.project.ui

import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableIntStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
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.minus
import kotlinx.datetime.plus

/**
 * 月度日历网格页，6×7 布局，支持折叠动画。
 *
 * 折叠时选中行保持原高，上方行向上收缩、下方行向下收缩，模拟"挤压"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（6行），1f=折叠（仅选中行可见）
 * @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,
    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 } }
    }

    var rowHeightPx by remember { mutableIntStateOf(0) }

    Column(modifier = modifier) {
        weeks.forEachIndexed { weekIndex, week ->
            val isAboveSelected = weekIndex < selectedWeekIndex
            val isBelowSelected = weekIndex > selectedWeekIndex

            val rowScale = when {
                isAboveSelected || isBelowSelected -> 1f - collapseProgress
                else -> 1f
            }

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

            if (rowHeightDp > 0.dp) {
                Row(
                    modifier = Modifier
                        .fillMaxWidth()
                        .height(rowHeightDp)
                        .onSizeChanged { size ->
                            if (weekIndex == 0 && size.height > 0) {
                                rowHeightPx = size.height
                            }
                        }
                        .padding(vertical = 2.dp)
                ) {
                    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))

    // 6行×7列=42格，覆盖跨月首尾周，保证网格完整
    return (0 until 42).map { i ->
        val date = startDate.plus(DatePeriod(days = i))
        DayData(
            date = date,
            isCurrentMonth = date.monthNumber == month && date.year == year
        )
    }
}