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.clickable
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
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.layout.widthIn
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.ArrowDropDown
import androidx.compose.material.icons.filled.Refresh
import androidx.compose.material3.CircularProgressIndicator
import androidx.compose.material3.DropdownMenu
import androidx.compose.material3.DropdownMenuItem
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.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
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(state.groupName ?: "Расписание", style = MaterialTheme.typography.titleMedium) },
            actions = {
                TextButton(onClick = { onSwitchGroup() }) {
                    Text("Сменить группу")
                }
                IconButton(onClick = { viewModel.refresh() }) {
                    Icon(Icons.Default.Refresh, contentDescription = "Обновить")
                }
            },
            windowInsets = WindowInsets(0.dp)
        )
        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 ""

                        Row(
                            Modifier.fillMaxWidth(),
                            verticalAlignment = Alignment.CenterVertically
                        ) {
                            Text(
                                "$dayLabel${dayName(day.date.dayOfWeek)} · ${day.date.format(FULL_DATE)}",
                                style = MaterialTheme.typography.titleMedium,
                                modifier = Modifier.weight(1f)
                            )
                            WeekSelector(
                                periods = schedule.periods,
                                selectedWeekStart = state.weekStart,
                                todayWeekStart = state.todayDate?.let { schedule.periodOf(it)?.weekStart },
                                onSelect = viewModel::selectWeek
                            )
                        }
                        HorizontalDivider(Modifier.padding(top = 8.dp, bottom = 0.dp))

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

                        HorizontalDivider(Modifier.padding(top=0.dp, bottom = 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)
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

@OptIn(ExperimentalMaterial3Api::class)
@Composable
private fun WeekSelector(
    periods: List<SchedulePeriod>,
    selectedWeekStart: LocalDate?,
    todayWeekStart: LocalDate?,
    onSelect: (LocalDate) -> Unit
) {
    val selected = periods.firstOrNull { it.weekStart == selectedWeekStart }
    var expanded by remember { mutableStateOf(false) }

    Box {
        Row(
            modifier = Modifier
                .clip(MaterialTheme.shapes.small)
                .clickable(enabled = true, onClick = { expanded = true })
                .padding(horizontal = 10.dp, vertical = 8.dp),
            verticalAlignment = Alignment.CenterVertically
        ) {
            Text(
                selected?.let(::weekLabel) ?: "Период",
                style = MaterialTheme.typography.labelLarge,
                color = MaterialTheme.colorScheme.primary
            )
            Icon(
                imageVector = Icons.Default.ArrowDropDown,
                contentDescription = null,
                tint = MaterialTheme.colorScheme.primary
            )
        }
        DropdownMenu(
            expanded = expanded,
            onDismissRequest = { expanded = false },
            modifier = Modifier.widthIn(min = 220.dp)
        ) {
            periods.forEach { period ->
                val isTodayWeek = todayWeekStart == period.weekStart
                DropdownMenuItem(
                    text = {
                        Text(
                            weekLabel(period),
                            style = MaterialTheme.typography.bodyLarge
                        )
                    },
                    trailingIcon = if (isTodayWeek) {
                        {
                            Text(
                                "сегодня",
                                style = MaterialTheme.typography.labelMedium,
                                color = MaterialTheme.colorScheme.primary
                            )
                        }
                    } else {
                        null
                    },
                    onClick = {
                        expanded = false
                        onSelect(period.weekStart)
                    }
                )
            }
        }
    }
}

@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.type.label,
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant
                    )

                    Text(
                        lesson.subject?.takeIf { it.isNotBlank() } ?: lesson.raw,
                        style = MaterialTheme.typography.bodyLarge
                    )
                    Text(
                        listOfNotNull(
                            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")