package agzam.vyatsu.ui.schedule

import agzam.vyatsu.domain.ScheduleDates
import agzam.vyatsu.domain.model.Schedule
import agzam.vyatsu.domain.repository.PreferencesRepository
import agzam.vyatsu.domain.repository.ScheduleRepository
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch
import java.time.LocalDate

class ScheduleViewModel(
    private val scheduleRepository: ScheduleRepository,
    private val preferencesRepository: PreferencesRepository
) : ViewModel() {

    private val _uiState = MutableStateFlow(ScheduleUiState())
    val uiState: StateFlow<ScheduleUiState> = _uiState.asStateFlow()

    private var currentGroupId: String? = null

    init {
        viewModelScope.launch {
            val groupId = preferencesRepository.selectedGroupId()
            if (groupId != null) {
                selectGroup(groupId)
            } else {
                _uiState.value = _uiState.value.copy(noGroup = true)
            }
        }
    }

    fun selectGroup(groupId: String) {
        currentGroupId = groupId
        viewModelScope.launch {
            preferencesRepository.setSelectedGroup(groupId)

            val savedWeekStart = runCatching {
                preferencesRepository.selectedWeekStart()?.let(LocalDate::parse)
            }.getOrNull()
            val savedDayDate = runCatching {
                preferencesRepository.selectedDayDate()?.let(LocalDate::parse)
            }.getOrNull()
            _uiState.value = _uiState.value.copy(
                noGroup = false,
                weekStart = savedWeekStart,
                dayDate = savedDayDate
            )

            launch {
                scheduleRepository.observeSchedule(groupId).collect { schedule ->
                    currentGroupId?.let { applySchedule(schedule) }
                }
            }

            launch {
                syncIfMissingToday(groupId)
            }
        }
    }

    private suspend fun applySchedule(schedule: Schedule?) {
        val current = _uiState.value
        if (schedule == null || schedule.periods.isEmpty()) {
            _uiState.value = current.copy(schedule = schedule, todayDate = null)
            return
        }
        val today = ScheduleDates.moscowToday()
        val todayDate = if (schedule.periodOf(today) != null) today else null

        val weekStart = when {
            schedule.periods.any { it.weekStart == current.weekStart } -> current.weekStart!!
            todayDate != null -> schedule.periodOf(todayDate)!!.weekStart
            else -> schedule.periods.first().weekStart
        }
        val period = schedule.periods.first { it.weekStart == weekStart }
        val weekDays = schedule.daysOf(period)

        val dayDate = when {
            weekDays.any { it.date == current.dayDate } -> current.dayDate
            weekDays.any { it.date == todayDate && todayDate != null } -> todayDate
            else -> weekDays.firstOrNull()?.date
        }

        preferencesRepository.setSelectedWeekStart(weekStart.toString())
        dayDate?.let { preferencesRepository.setSelectedDayDate(it.toString()) }

        _uiState.value = current.copy(
            schedule = schedule,
            weekStart = weekStart,
            dayDate = dayDate,
            todayDate = todayDate
        )
    }

    fun selectWeek(weekStart: LocalDate) {
        val state = _uiState.value
        val schedule = state.schedule ?: return
        val period = schedule.periods.firstOrNull { it.weekStart == weekStart } ?: return
        viewModelScope.launch {
            val today = ScheduleDates.moscowToday()
            val weekDays = schedule.daysOf(period)
            val dayDate = when {
                weekDays.any { it.date == today } -> today
                else -> weekDays.firstOrNull()?.date
            }
            preferencesRepository.setSelectedWeekStart(weekStart.toString())
            dayDate?.let { preferencesRepository.setSelectedDayDate(it.toString()) }
            _uiState.value = _uiState.value.copy(weekStart = weekStart, dayDate = dayDate)
        }
    }

    fun selectDay(date: LocalDate) {
        val state = _uiState.value
        val schedule = state.schedule ?: return
        val period = schedule.periodOf(date) ?: return
        viewModelScope.launch {
            preferencesRepository.setSelectedWeekStart(period.weekStart.toString())
            preferencesRepository.setSelectedDayDate(date.toString())
            _uiState.value = _uiState.value.copy(weekStart = period.weekStart, dayDate = date)
        }
    }

    private suspend fun syncIfMissingToday(groupId: String) {
        val schedule = scheduleRepository.getSchedule(groupId)
        val today = ScheduleDates.moscowToday()
        val hasTodayPeriod = schedule?.periodOf(today) != null
        if (hasTodayPeriod) return
        _uiState.value = _uiState.value.copy(isSyncing = true)
        scheduleRepository.sync(groupId)
        _uiState.value = _uiState.value.copy(isSyncing = false)
    }

    fun switchGroup() {
        viewModelScope.launch {
            currentGroupId = null
            preferencesRepository.clearSelectedGroup()
            _uiState.value = _uiState.value.copy(noGroup = true)
        }
    }

    fun refresh() {
        val groupId = currentGroupId ?: return
        viewModelScope.launch {
            _uiState.value = _uiState.value.copy(isRefreshing = true)
            scheduleRepository.sync(groupId)
            _uiState.value = _uiState.value.copy(isRefreshing = false)
        }
    }

    fun clearAll() {
        val groupId = currentGroupId ?: return
        viewModelScope.launch {
            scheduleRepository.clearAll(groupId)
        }
    }

    fun clearSelectedPeriod() {
        val state = _uiState.value
        val schedule = state.schedule ?: return
        val weekStart = state.weekStart ?: return
        val period = schedule.periods.firstOrNull { it.weekStart == weekStart } ?: return
        viewModelScope.launch {
            scheduleRepository.clearPeriod(schedule.groupId, period)
        }
    }
}

data class ScheduleUiState(
    val noGroup: Boolean = false,
    val isRefreshing: Boolean = false,
    val isSyncing: Boolean = false,
    val schedule: Schedule? = null,
    val weekStart: LocalDate? = null,
    val dayDate: LocalDate? = null,
    val todayDate: LocalDate? = null
)