package agzam.vyatsu.ui.schedule

import agzam.vyatsu.domain.model.Day
import agzam.vyatsu.domain.model.SchedulePeriod
import agzam.vyatsu.domain.model.TimeSlot
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.WindowInsets
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.only
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.systemBars
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.LazyRow
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.lazy.itemsIndexed
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Refresh
import androidx.compose.material3.CircularProgressIndicator
import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.FilterChip
import androidx.compose.material3.FilterChipDefaults
import androidx.compose.material3.HorizontalDivider
import androidx.compose.material3.Icon
import androidx.compose.material3.IconButton
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
import androidx.compose.material3.TextButton
import androidx.compose.material3.TopAppBar
import androidx.compose.runtime.Composable
import androidx.compose.runtime.collectAsState
import androidx.compose.runtime.getValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
import java.time.DayOfWeek
import java.time.LocalDate
import java.time.format.DateTimeFormatter

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun ScheduleScreen(viewModel: ScheduleViewModel, onSwitchGroup: () -> Unit) {
    val state by viewModel.uiState.collectAsState()

    Column(Modifier.fillMaxSize()) {
        TopAppBar(
            title = { Text("Расписание") },
            actions = {
                TextButton(onClick = { onSwitchGroup() }) {
                    Text("Сменить группу")
                }
                IconButton(onClick = { viewModel.refresh() }) {
                    Icon(Icons.Default.Refresh, contentDescription = "Обновить")
                }
            },
            windowInsets = WindowInsets.systemBars.only(androidx.compose.foundation.layout.WindowInsetsSides.Top)
        )
        Column(Modifier.fillMaxSize().padding(horizontal = 16.dp, vertical = 0.dp)) {
            when {
                state.isSyncing && state.schedule == null -> {
                    Row(
                        Modifier.fillMaxWidth(),
                        horizontalArrangement = Arrangement.Center
                    ) {
                        CircularProgressIndicator()
                    }
                }

                state.schedule == null -> {
                    Column(
                        Modifier.fillMaxWidth(),
                        horizontalAlignment = Alignment.CenterHorizontally
                    ) {
                        Text(
                            "Не удалось загрузить расписание",
                            style = MaterialTheme.typography.bodyLarge
                        )
                        TextButton(onClick = { viewModel.refresh() }) {
                            Text("Повторить")
                        }
                    }
                }

                else -> {
                    val schedule = state.schedule!!
                    val weekDays = state.weekStart
                        ?.let { ws -> schedule.periods.firstOrNull { it.weekStart == ws } }
                        ?.let { schedule.daysOf(it) }
                        .orEmpty()
                    val day = schedule.days.firstOrNull { it.date == state.dayDate }

                    if (day == null) {
                        Text("Занятий нет", style = MaterialTheme.typography.bodyLarge)
                    } else {
                        val isTodayDay = day.date == state.todayDate
                        val dayLabel = if (isTodayDay) "Сегодня " else ""

                        Text(
                            "$dayLabel ${dayName(day.date.dayOfWeek)} · ${day.date.format(FULL_DATE)}",
                            style = MaterialTheme.typography.titleMedium
                        )
                        Row(
                            Modifier.fillMaxWidth(),
                            horizontalArrangement = Arrangement.spacedBy(8.dp)
                        ) {
                            TextButton(onClick = { viewModel.clearSelectedPeriod() }) {
                                Text("Очистить эту неделю")
                            }
                            TextButton(onClick = { viewModel.clearAll() }) {
                                Text("Очистить всё")
                            }
                        }
                        HorizontalDivider(Modifier.padding(vertical = 8.dp))

                        WeekChips(
                            periods = schedule.periods,
                            selectedWeekStart = state.weekStart,
                            todayWeekStart = state.todayDate?.let { schedule.periodOf(it)?.weekStart },
                            onSelect = viewModel::selectWeek
                        )

                        HorizontalDivider(Modifier.padding(vertical = 8.dp))

                        DayChips(
                            days = weekDays,
                            selectedDate = state.dayDate,
                            todayDate = state.todayDate,
                            onSelect = viewModel::selectDay
                        )

                        HorizontalDivider(Modifier.padding(vertical = 8.dp))

                        if (day.intervals.all { it.lessons.isEmpty() }) {
                            Text("Занятий нет", style = MaterialTheme.typography.bodyLarge)
                        } else {
                            LazyColumn(
                                modifier = Modifier.weight(1f),
                                verticalArrangement = Arrangement.spacedBy(8.dp)
                            ) {
                                itemsIndexed(day.intervals) { slotIndex, slot ->
                                    LessonSlot(slotIndex = slotIndex, slot = slot)
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

@Composable
private fun WeekChips(
    periods: List<SchedulePeriod>,
    selectedWeekStart: LocalDate?,
    todayWeekStart: LocalDate?,
    onSelect: (LocalDate) -> Unit
) {
    LazyRow(horizontalArrangement = Arrangement.spacedBy(6.dp)) {
        items(periods, key = { it.weekStart.toEpochDay() }) { period ->
            val selected = selectedWeekStart == period.weekStart
            val isTodayWeek = todayWeekStart == period.weekStart
            FilterChip(
                selected = selected,
                onClick = { onSelect(period.weekStart) },
                label = {
                    Text(
                        weekLabel(period),
                        style = MaterialTheme.typography.labelLarge
                    )
                },
                modifier = Modifier.padding(vertical = 2.dp),
                border = if (isTodayWeek && !selected) {
                    FilterChipDefaults.filterChipBorder(
                        borderColor = MaterialTheme.colorScheme.primary,
                        borderWidth = 1.dp,
                        enabled = true,
                        selected = false
                    )
                } else {
                    FilterChipDefaults.filterChipBorder(enabled = true, selected = selected)
                },
                shape = RoundedCornerShape(8.dp)
            )
        }
    }
}

@Composable
private fun DayChips(
    days: List<Day>,
    selectedDate: LocalDate?,
    todayDate: LocalDate?,
    onSelect: (LocalDate) -> Unit
) {
    LazyRow(horizontalArrangement = Arrangement.spacedBy(6.dp)) {
        items(days, key = { it.date.toEpochDay() }) { day ->
            val selected = selectedDate == day.date
            val isTodayChip = todayDate == day.date
            FilterChip(
                selected = selected,
                onClick = { onSelect(day.date) },
                label = {
                    Column(horizontalAlignment = Alignment.CenterHorizontally) {
                        Text(
                            dayName(day.date.dayOfWeek),
                            style = MaterialTheme.typography.labelMedium
                        )
                        Text(
                            day.date.format(CHIP_DATE),
                            style = MaterialTheme.typography.labelSmall,
                            color = if (selected) {
                                MaterialTheme.colorScheme.onSecondaryContainer
                            } else {
                                MaterialTheme.colorScheme.onSurfaceVariant
                            }
                        )
                    }
                },
                modifier = Modifier.padding(vertical = 2.dp),
                border = if (isTodayChip && !selected) {
                    FilterChipDefaults.filterChipBorder(
                        borderColor = MaterialTheme.colorScheme.primary,
                        borderWidth = 1.dp,
                        enabled = true,
                        selected = false
                    )
                } else {
                    FilterChipDefaults.filterChipBorder(enabled = true, selected = selected)
                },
                shape = RoundedCornerShape(8.dp)
            )
        }
    }
}

private fun weekLabel(period: SchedulePeriod): String {
    val first = period.weekStart
    return "с ${first.format(CHIP_DATE)}"
}

@Composable
private fun LessonSlot(slotIndex: Int, slot: TimeSlot) {
    Column(Modifier.fillMaxWidth()) {
        Text(
            "${slotIndex + 1} пара · ${slot.start.format(TIME)}–${slot.end.format(TIME)}",
            style = MaterialTheme.typography.labelMedium,
            color = MaterialTheme.colorScheme.primary
        )
        if (slot.lessons.isEmpty()) {
            Text("—", style = MaterialTheme.typography.bodyMedium)
        } else {
            slot.lessons.forEach { lesson ->
                Column(Modifier.fillMaxWidth().padding(vertical = 2.dp)) {
                    Text(
                        lesson.subject?.takeIf { it.isNotBlank() } ?: lesson.raw,
                        style = MaterialTheme.typography.bodyLarge
                    )
                    Text(
                        listOfNotNull(
                            lesson.type.label,
                            lesson.subgroup,
                            lesson.teacher,
                            lesson.room
                        )
                            .filter { it.isNotBlank() }
                            .joinToString(" · "),
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant
                    )
                }
            }
        }
    }
}

private fun dayName(dayOfWeek: DayOfWeek): String = when (dayOfWeek) {
    DayOfWeek.MONDAY -> "Пн"
    DayOfWeek.TUESDAY -> "Вт"
    DayOfWeek.WEDNESDAY -> "Ср"
    DayOfWeek.THURSDAY -> "Чт"
    DayOfWeek.FRIDAY -> "Пт"
    DayOfWeek.SATURDAY -> "Сб"
    DayOfWeek.SUNDAY -> "Вс"
}

private val FULL_DATE: DateTimeFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy")
private val CHIP_DATE: DateTimeFormatter = DateTimeFormatter.ofPattern("dd.MM")
private val TIME: DateTimeFormatter = DateTimeFormatter.ofPattern("HH:mm")