package service

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

	"github.com/google/uuid"
	"github.com/wotra/wotra/internal/domain"
	"github.com/wotra/wotra/internal/store"
)

// Sentinel errors returned by the service layer.
var (
	ErrEntryRunning      = errors.New("an entry is already running")
	ErrEntryNotRunning   = errors.New("no running entry found")
	ErrEntryNotFound     = errors.New("entry not found")
	ErrDayAlreadyClosed  = errors.New("day is already closed")
	ErrDayNotClosed      = errors.New("day is not closed")
	ErrRunningEntryOnDay = errors.New("a running entry exists for this day; stop it first")
	ErrCrossesMidnight   = errors.New("entry end_time must be on the same calendar day as start_time")
)

// EntryService handles business logic for time entries.
type EntryService struct {
	entries     *store.EntryStore
	closedDays  *store.ClosedDayStore
	settings    *store.SettingsStore
	tz          *time.Location
}

func NewEntryService(
	entries *store.EntryStore,
	closedDays *store.ClosedDayStore,
	settings *store.SettingsStore,
	tz *time.Location,
) *EntryService {
	return &EntryService{
		entries:    entries,
		closedDays: closedDays,
		settings:   settings,
		tz:         tz,
	}
}

func (s *EntryService) nowMs() int64 {
	return time.Now().UnixMilli()
}

func (s *EntryService) dayKeyForMs(ms int64) string {
	t := time.UnixMilli(ms).In(s.tz)
	return t.Format("2006-01-02")
}

// midnightEndMs returns the unix ms of 23:59:59.999 for the day containing ms in the configured tz.
func (s *EntryService) midnightEndMs(ms int64) int64 {
	t := time.UnixMilli(ms).In(s.tz)
	end := time.Date(t.Year(), t.Month(), t.Day(), 23, 59, 59, 999_000_000, s.tz)
	return end.UnixMilli()
}

// Start creates a new running entry. Returns ErrEntryRunning if one is already active.
func (s *EntryService) Start(ctx context.Context, note string) (*domain.Entry, error) {
	running, err := s.entries.RunningEntry(ctx)
	if err != nil {
		return nil, err
	}
	if running != nil {
		return nil, ErrEntryRunning
	}

	nowMs := s.nowMs()
	dayKey := s.dayKeyForMs(nowMs)

	// Check day is not already closed
	closed, err := s.closedDays.GetByDayKey(ctx, dayKey)
	if err != nil && !errors.Is(err, sql.ErrNoRows) {
		return nil, err
	}
	if closed != nil {
		return nil, ErrDayAlreadyClosed
	}

	e := &domain.Entry{
		ID:        uuid.New().String(),
		StartTime: nowMs,
		Note:      note,
		DayKey:    dayKey,
		UpdatedAt: nowMs,
	}
	if err := s.entries.Create(ctx, e); err != nil {
		return nil, err
	}
	return e, nil
}

// Stop stops the currently running entry. Returns ErrEntryNotRunning if none active.
func (s *EntryService) Stop(ctx context.Context) (*domain.Entry, error) {
	running, err := s.entries.RunningEntry(ctx)
	if err != nil {
		return nil, err
	}
	if running == nil {
		return nil, ErrEntryNotRunning
	}
	return s.stopEntry(ctx, running, false)
}

// StopByID stops a specific entry by ID.
func (s *EntryService) StopByID(ctx context.Context, id string) (*domain.Entry, error) {
	e, err := s.entries.GetByID(ctx, id)
	if err == sql.ErrNoRows {
		return nil, ErrEntryNotFound
	}
	if err != nil {
		return nil, err
	}
	if !e.IsRunning() {
		return nil, ErrEntryNotRunning
	}
	return s.stopEntry(ctx, e, false)
}

func (s *EntryService) stopEntry(ctx context.Context, e *domain.Entry, autoStopped bool) (*domain.Entry, error) {
	nowMs := s.nowMs()

	// Enforce same-day rule: cap end_time at 23:59:59.999 of start day
	endMs := nowMs
	startDayKey := s.dayKeyForMs(e.StartTime)
	endDayKey := s.dayKeyForMs(endMs)
	if endDayKey != startDayKey {
		// Cross-midnight: cap at end of start day
		endMs = s.midnightEndMs(e.StartTime)
		autoStopped = true
	}

	e.EndTime = &endMs
	e.AutoStopped = autoStopped
	e.UpdatedAt = nowMs

	if err := s.entries.Update(ctx, e); err != nil {
		return nil, err
	}
	return e, nil
}

// GetByID returns a single entry.
func (s *EntryService) GetByID(ctx context.Context, id string) (*domain.Entry, error) {
	e, err := s.entries.GetByID(ctx, id)
	if err == sql.ErrNoRows {
		return nil, ErrEntryNotFound
	}
	return e, err
}

// List returns entries within a date range.
func (s *EntryService) List(ctx context.Context, fromDayKey, toDayKey string) ([]*domain.Entry, error) {
	return s.entries.ListByDateRange(ctx, fromDayKey, toDayKey)
}

// UpdateEntry allows editing start/end/note for a non-running, non-closed entry.
type UpdateEntryInput struct {
	StartTime *int64
	EndTime   *int64
	Note      *string
}

func (s *EntryService) Update(ctx context.Context, id string, input UpdateEntryInput) (*domain.Entry, error) {
	e, err := s.entries.GetByID(ctx, id)
	if err == sql.ErrNoRows {
		return nil, ErrEntryNotFound
	}
	if err != nil {
		return nil, err
	}

	if input.StartTime != nil {
		e.StartTime = *input.StartTime
		e.DayKey = s.dayKeyForMs(e.StartTime)
	}
	if input.EndTime != nil {
		// Validate same-day
		startDayKey := s.dayKeyForMs(e.StartTime)
		endDayKey := s.dayKeyForMs(*input.EndTime)
		if startDayKey != endDayKey {
			return nil, ErrCrossesMidnight
		}
		if *input.EndTime < e.StartTime {
			return nil, fmt.Errorf("end_time must be after start_time")
		}
		e.EndTime = input.EndTime
	}
	if input.Note != nil {
		e.Note = *input.Note
	}

	e.UpdatedAt = s.nowMs()
	if err := s.entries.Update(ctx, e); err != nil {
		return nil, err
	}
	return e, nil
}

// Delete soft-deletes an entry.
func (s *EntryService) Delete(ctx context.Context, id string) error {
	nowMs := s.nowMs()
	return s.entries.SoftDelete(ctx, id, nowMs)
}

// AutoStopStalledEntries stops any running entries whose day_key is before today.
// Called by the midnight background goroutine.
func (s *EntryService) AutoStopStalledEntries(ctx context.Context) ([]string, error) {
	today := s.dayKeyForMs(s.nowMs())
	return s.entries.StopAllRunningBefore(ctx, today, s.nowMs(), s.nowMs())
}