package service

import (
	"context"
	"database/sql"
	"errors"
	"time"

	"github.com/wotra/wotra/internal/domain"
	"github.com/wotra/wotra/internal/store"
)
var (
	ErrWeekAlreadyClosed     = errors.New("week is already closed")
	ErrWeekNotClosed         = errors.New("week is not closed")
	ErrWeekHasUnclosedDays   = errors.New("all workdays in the week must be closed before closing the week")
	ErrDayHasNoEntries       = errors.New("no completed entries found for this day")
)

// DayService handles closing and marking days.
type DayService struct {
	entries     *store.EntryStore
	closedDays  *store.ClosedDayStore
	closedWeeks *store.ClosedWeekStore
	settings    *store.SettingsStore
	tz          *time.Location
}

func NewDayService(
	entries *store.EntryStore,
	closedDays *store.ClosedDayStore,
	closedWeeks *store.ClosedWeekStore,
	settings *store.SettingsStore,
	tz *time.Location,
) *DayService {
	return &DayService{
		entries:     entries,
		closedDays:  closedDays,
		closedWeeks: closedWeeks,
		settings:    settings,
		tz:          tz,
	}
}

// recomputeWeek updates worked_ms/delta_ms on the closed week containing dayKey,
// if that week is already closed. Called after any day close/reopen.
func (s *DayService) recomputeWeek(ctx context.Context, dayKey string) error {
	weekKey, err := WeekKeyForDayKey(dayKey, s.tz)
	if err != nil {
		return err
	}
	cw, err := s.closedWeeks.GetByWeekKey(ctx, weekKey)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil // week not closed yet — nothing to do
		}
		return err
	}
	// Recompute worked_ms from all closed days in the week.
	dayKeys, err := weekDayKeys(weekKey, s.tz)
	if err != nil {
		return err
	}
	var totalWorkedMs int64
	for _, dk := range dayKeys {
		cd, err := s.closedDays.GetByDayKey(ctx, dk)
		if err != nil {
			if errors.Is(err, sql.ErrNoRows) {
				continue
			}
			return err
		}
		totalWorkedMs += cd.WorkedMs
	}
	cw.WorkedMs = totalWorkedMs
	cw.DeltaMs = totalWorkedMs - cw.ExpectedMs
	cw.UpdatedAt = time.Now().UnixMilli()
	return s.closedWeeks.Upsert(ctx, cw)
}

// CloseDay merges all completed entries for the given day key into a ClosedDay.
// Returns ErrRunningEntryOnDay if a running entry exists.
// Returns ErrDayAlreadyClosed if already closed.
func (s *DayService) CloseDay(ctx context.Context, dayKey string) (*domain.ClosedDay, error) {
	// Already closed?
	existing, err := s.closedDays.GetByDayKey(ctx, dayKey)
	if err != nil && !errors.Is(err, sql.ErrNoRows) {
		return nil, err
	}
	if existing != nil {
		return nil, ErrDayAlreadyClosed
	}

	// Running entry?
	running, err := s.entries.RunningEntryForDay(ctx, dayKey)
	if err != nil {
		return nil, err
	}
	if running != nil {
		return nil, ErrRunningEntryOnDay
	}

	// Load all completed entries for the day
	entries, err := s.entries.ListByDayKey(ctx, dayKey)
	if err != nil {
		return nil, err
	}
	if len(entries) == 0 {
		return nil, ErrDayHasNoEntries
	}

	var minStart, maxEnd, totalMs int64
	minStart = entries[0].StartTime
	for _, e := range entries {
		if e.EndTime == nil {
			continue
		}
		if e.StartTime < minStart {
			minStart = e.StartTime
		}
		if *e.EndTime > maxEnd {
			maxEnd = *e.EndTime
		}
		totalMs += e.DurationMs()
	}

	now := time.Now().UnixMilli()
	cd := &domain.ClosedDay{
		DayKey:    dayKey,
		StartTime: &minStart,
		EndTime:   &maxEnd,
		WorkedMs:  totalMs,
		Kind:      domain.DayKindWork,
		ClosedAt:  now,
		UpdatedAt: now,
	}
	if err := s.closedDays.Upsert(ctx, cd); err != nil {
		return nil, err
	}
	if err := s.recomputeWeek(ctx, dayKey); err != nil {
		return nil, err
	}
	return cd, nil
}

// MarkDay closes a day as holiday, vacation, or sick.
// worked_ms is set to the expected daily ms from settings at that date.
func (s *DayService) MarkDay(ctx context.Context, dayKey string, kind domain.DayKind) (*domain.ClosedDay, error) {
	if !kind.Valid() || kind == domain.DayKindWork {
		return nil, errors.New("kind must be one of: holiday, vacation, sick")
	}

	// Lookup settings effective on that day
	set, err := s.settings.Current(ctx, dayKey)
	if err != nil && !errors.Is(err, sql.ErrNoRows) {
		return nil, err
	}

	var workedMs int64
	if set != nil {
		// Parse the weekday from dayKey
		t, err := time.ParseInLocation("2006-01-02", dayKey, s.tz)
		if err == nil && set.IsWorkday(int(t.Weekday())) {
			workedMs = set.DailyExpectedMs()
		}
	}

	now := time.Now().UnixMilli()
	cd := &domain.ClosedDay{
		DayKey:    dayKey,
		WorkedMs:  workedMs,
		Kind:      kind,
		ClosedAt:  now,
		UpdatedAt: now,
	}
	if err := s.closedDays.Upsert(ctx, cd); err != nil {
		return nil, err
	}
	if err := s.recomputeWeek(ctx, dayKey); err != nil {
		return nil, err
	}
	return cd, nil
}

// ReopenDay deletes the closed_days row for a day, making it editable again.
func (s *DayService) ReopenDay(ctx context.Context, dayKey string) error {
	existing, err := s.closedDays.GetByDayKey(ctx, dayKey)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return ErrDayNotClosed
		}
		return err
	}
	if existing == nil {
		return ErrDayNotClosed
	}
	if err := s.closedDays.Delete(ctx, dayKey); err != nil {
		return err
	}
	return s.recomputeWeek(ctx, dayKey)
}

// GetDay returns the closed day for a given day key, or nil if open.
func (s *DayService) GetDay(ctx context.Context, dayKey string) (*domain.ClosedDay, error) {
	cd, err := s.closedDays.GetByDayKey(ctx, dayKey)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, nil
	}
	return cd, err
}

// ListDays returns closed days within a date range.
func (s *DayService) ListDays(ctx context.Context, fromDayKey, toDayKey string) ([]*domain.ClosedDay, error) {
	return s.closedDays.ListByDateRange(ctx, fromDayKey, toDayKey)
}