package lobby

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"sync/atomic"
	"time"
)

// Errors returned by the lobby service.
var (
	ErrRaceNotFound      = errors.New("race not found")
	ErrRaceFull          = errors.New("race is full")
	ErrRaceNotOpen       = errors.New("race is not open for joining")
	ErrRaceAlreadyExists = errors.New("race already exists")
	ErrDriverNotFound    = errors.New("driver not found")
	ErrInvalidInput      = errors.New("invalid input")
)

// Options for CreateRace.
type CreateRaceOptions struct {
	ID         string // optional; auto-generated if empty
	Name       string // required
	TrackID    string // optional, defaults to "default"
	MaxCars    int    // required, 1..8
	Laps       int    // 0 = time-based
	TimeLimitS int    // 0 = lap-based
}

// DefaultMaxCars is the fallback when CreateRaceOptions doesn't specify.
const DefaultMaxCars = 4

// raceCounter assigns sequential IDs when caller doesn't provide one.
var raceCounter seqCounter

// CreateRace registers a new race in the lobby.
//
// Rules:
//   - race name is required (non-empty)
//   - max_cars must be in [1, 8]
//   - laps and time_limit_s can't both be 0
//
// Races are owned by a physical track; there is no host driver. Drivers
// join via AddDriverToRace.
func (s *Service) CreateRace(opts CreateRaceOptions) (RaceMeta, error) {
	name := strings.TrimSpace(opts.Name)
	if name == "" {
		return RaceMeta{}, fmt.Errorf("%w: name required", ErrInvalidInput)
	}
	max := opts.MaxCars
	if max == 0 {
		max = DefaultMaxCars
	}
	if max < 1 || max > 8 {
		return RaceMeta{}, fmt.Errorf("%w: max_cars must be 1..8", ErrInvalidInput)
	}
	if opts.Laps == 0 && opts.TimeLimitS == 0 {
		return RaceMeta{}, fmt.Errorf("%w: laps or time_limit_s required", ErrInvalidInput)
	}

	s.mu.Lock()
	id := opts.ID
	if id == "" {
		id = fmt.Sprintf("race-%d-%d", time.Now().Unix(), raceCounter.v.Add(1))
	} else if _, exists := s.races[id]; exists {
		s.mu.Unlock()
		return RaceMeta{}, ErrRaceAlreadyExists
	}

	track := opts.TrackID
	if track == "" {
		track = "default"
	}

	meta := RaceMeta{
		ID:         id,
		Name:       name,
		TrackID:    track,
		MaxCars:    max,
		Laps:       opts.Laps,
		TimeLimitS: opts.TimeLimitS,
		DriverIDs:  []string{},
		Status:     RaceStatusLobby,
		CreatedMs:  time.Now().UnixMilli(),
	}

	s.races[id] = &meta
	hook := s.onRaceCreated
	s.mu.Unlock()

	if hook != nil {
		hook(meta)
	}
	s.bump("race_created", id, "")
	s.mirror(func(ctx context.Context, p Persistence) error { return p.UpsertRace(ctx, meta) })
	return meta, nil
}

// AddRace inserts a race into the in-memory lobby without triggering a
// persistence write. Used by RestoreFromDB where the row is already
// in Postgres. Bumps the lobby version so subscribers re-sync.
func (s *Service) AddRace(r RaceMeta) {
	if r.ID == "" {
		return
	}
	s.mu.Lock()
	r2 := r
	s.races[r.ID] = &r2
	s.mu.Unlock()
	s.bump("race_restored", r.ID, "")
}

// AddDriver registers a new driver or refreshes an existing one.
// If the driver already exists with a different name, the name is updated.
func (s *Service) AddDriver(id, name, country string) (DriverMeta, error) {
	if id == "" {
		return DriverMeta{}, fmt.Errorf("%w: id required", ErrInvalidInput)
	}
	if name == "" {
		name = id
	}

	s.mu.Lock()
	now := time.Now().UnixMilli()
	broadcastKind := ""
	if existing, ok := s.drivers[id]; ok {
		existing.LastSeenMs = now
		if name != "" {
			existing.Name = name
		}
		if country != "" {
			existing.Country = country
		}
		if existing.Status == DriverStatusOffline {
			existing.Status = DriverStatusIdle
			broadcastKind = "driver_joined"
		}
		out := *existing
		s.mu.Unlock()
		if broadcastKind != "" {
			s.bump(broadcastKind, "", id)
		}
		return out, nil
	}
	d := DriverMeta{
		ID:          id,
		Name:        name,
		Status:      DriverStatusIdle,
		ConnectedMs: now,
		LastSeenMs:  now,
		Country:     country,
		AvatarHue:   hashHue(id),
	}
	s.drivers[id] = &d
	s.mu.Unlock()
	s.bump("driver_joined", "", id)
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.UpsertDriver(ctx, d)
	})
	return d, nil
}

// RemoveDriver marks a driver as offline. The driver is kept in memory
// briefly to allow reconnect grace (see Snapshot filter).
func (s *Service) RemoveDriver(id string) {
	var raceIDToRemove string
	s.mu.Lock()
	d, ok := s.drivers[id]
	if !ok {
		s.mu.Unlock()
		return
	}
	// If still racing, treat as crash — remove from race.
	if d.Status == DriverStatusRacing && d.RaceID != "" {
		if race, ok := s.races[d.RaceID]; ok {
			race.DriverIDs = removeString(race.DriverIDs, id)
			if len(race.DriverIDs) == 0 {
				delete(s.races, d.RaceID)
				raceIDToRemove = d.RaceID
			}
		}
	}
	d.Status = DriverStatusOffline
	d.LastSeenMs = time.Now().UnixMilli()
	d.RaceID = ""
	hook := s.onRaceRemoved
	s.mu.Unlock()

	if raceIDToRemove != "" && hook != nil {
		hook(raceIDToRemove)
	}
	s.bump("driver_left", "", id)
	if raceIDToRemove != "" {
		s.mirror(func(ctx context.Context, p Persistence) error {
			return p.DeleteRace(context.Background(), raceIDToRemove)
		})
	}
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.DeleteDriver(ctx, id)
	})
}

// Heartbeat refreshes LastSeenMs (call periodically from session).
func (s *Service) Heartbeat(id string) {
	s.mu.Lock()
	if d, ok := s.drivers[id]; ok {
		d.LastSeenMs = time.Now().UnixMilli()
	}
	s.mu.Unlock()
}

// SetDriverProfile updates the denormalised display fields of a driver
// (nickname, avatar URL, clan). Safe to call on a missing driver (no-op).
func (s *Service) SetDriverProfile(id, nickname, avatarURL, clanID, clanTag string) {
	s.mu.Lock()
	var d *DriverMeta
	if v, ok := s.drivers[id]; ok {
		v.Nickname = nickname
		v.AvatarURL = avatarURL
		v.ClanID = clanID
		v.ClanTag = clanTag
		d = v
	}
	s.mu.Unlock()
	if d != nil {
		s.mirror(func(ctx context.Context, p Persistence) error {
			return p.UpsertDriver(ctx, *d)
		})
	}
}

// AddDriverToRace moves a driver from idle into a race. Used by the
// client->server JoinRace flow (in addition to the race engine state).
// Idempotent: re-joining the same race is a no-op.
func (s *Service) AddDriverToRace(driverID, raceID string) error {
	s.mu.Lock()
	d, ok := s.drivers[driverID]
	if !ok {
		s.mu.Unlock()
		return ErrDriverNotFound
	}
	r, ok := s.races[raceID]
	if !ok {
		s.mu.Unlock()
		return ErrRaceNotFound
	}
	if r.Status != RaceStatusLobby {
		s.mu.Unlock()
		return fmt.Errorf("%w: status=%s", ErrRaceNotOpen, r.Status)
	}
	if len(r.DriverIDs) >= r.MaxCars {
		s.mu.Unlock()
		return ErrRaceFull
	}
	if containsString(r.DriverIDs, driverID) {
		d.Status = DriverStatusRacing
		d.RaceID = raceID
		s.mu.Unlock()
		return nil
	}
	r.DriverIDs = append(r.DriverIDs, driverID)
	d.Status = DriverStatusRacing
	d.RaceID = raceID
	slot := len(r.DriverIDs) - 1
	s.mu.Unlock()
	s.bump("race_updated", raceID, driverID)
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.AddDriver(ctx, raceID, driverID, slot)
	})
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.UpsertDriver(ctx, *d)
	})
	return nil
}

// RemoveDriverFromRace returns a driver to the lobby.
func (s *Service) RemoveDriverFromRace(driverID string) {
	var raceIDRemoved string
	s.mu.Lock()
	d, ok := s.drivers[driverID]
	if !ok {
		s.mu.Unlock()
		return
	}
	if d.RaceID == "" {
		d.Status = DriverStatusIdle
		s.mu.Unlock()
		return
	}
	r, ok := s.races[d.RaceID]
	if ok {
		r.DriverIDs = removeString(r.DriverIDs, driverID)
		if len(r.DriverIDs) == 0 {
			delete(s.races, d.RaceID)
			raceIDRemoved = d.RaceID
		}
	}
	d.Status = DriverStatusIdle
	d.RaceID = ""
	prevRaceID := d.RaceID
	hook := s.onRaceRemoved
	s.mu.Unlock()

	if raceIDRemoved != "" && hook != nil {
		hook(raceIDRemoved)
	}
	s.bump("race_updated", prevRaceID, driverID)
	if prevRaceID != "" {
		s.mirror(func(ctx context.Context, p Persistence) error {
			return p.RemoveDriver(ctx, prevRaceID, driverID)
		})
	}
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.UpsertDriver(ctx, *d)
	})
	if raceIDRemoved != "" {
		s.mirror(func(ctx context.Context, p Persistence) error {
			return p.DeleteRace(ctx, raceIDRemoved)
		})
	}
}

// SetRaceStatus updates the status (used by Engine when race starts/ends).
func (s *Service) SetRaceStatus(raceID string, status RaceStatus) error {
	s.mu.Lock()
	r, ok := s.races[raceID]
	if !ok {
		s.mu.Unlock()
		return ErrRaceNotFound
	}
	r.Status = status
	if status == RaceStatusRacing && r.StartedMs == 0 {
		r.StartedMs = time.Now().UnixMilli()
	}
	startedMs := r.StartedMs
	var affected []DriverMeta
	if status == RaceStatusFinished {
		for _, did := range r.DriverIDs {
			if d, ok := s.drivers[did]; ok {
				d.Status = DriverStatusIdle
				d.RaceID = ""
				affected = append(affected, *d)
			}
		}
	}
	s.mu.Unlock()
	s.bump("race_updated", raceID, "")
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.SetRaceStatus(ctx, raceID, status, startedMs)
	})
	for i := range affected {
		d := affected[i]
		s.mirror(func(ctx context.Context, p Persistence) error {
			return p.UpsertDriver(ctx, d)
		})
	}
	return nil
}

// DeleteRace removes a race entirely. Drivers inside are returned to idle.
func (s *Service) DeleteRace(raceID string) error {
	s.mu.Lock()
	r, ok := s.races[raceID]
	if !ok {
		s.mu.Unlock()
		return ErrRaceNotFound
	}
	for _, did := range r.DriverIDs {
		if d, ok := s.drivers[did]; ok {
			d.Status = DriverStatusIdle
			d.RaceID = ""
		}
	}
	delete(s.races, raceID)
	hook := s.onRaceRemoved
	s.mu.Unlock()
	if hook != nil {
		hook(raceID)
	}
	s.bump("race_removed", raceID, "")
	s.mirror(func(ctx context.Context, p Persistence) error {
		return p.DeleteRace(ctx, raceID)
	})
	return nil
}

// QuickPlay assigns a driver to the first available race, or creates
// a new one if none exist. Returns the chosen race.
func (s *Service) QuickPlay(driverID string, defaultMaxCars int) (RaceMeta, error) {
	var candidateID string
	s.mu.RLock()
	for _, r := range s.races {
		if r.Status == RaceStatusLobby && len(r.DriverIDs) < r.MaxCars {
			candidateID = r.ID
			break
		}
	}
	s.mu.RUnlock()

	if candidateID != "" {
		if err := s.AddDriverToRace(driverID, candidateID); err != nil {
			return RaceMeta{}, err
		}
		return s.GetRace(candidateID)
	}
	driver, err := s.GetDriver(driverID)
	if err != nil {
		return RaceMeta{}, err
	}
	race, err := s.CreateRace(CreateRaceOptions{
		Name:    driver.Name + "'s race",
		MaxCars: defaultMaxCars,
		Laps:    5,
	})
	if err != nil {
		return RaceMeta{}, err
	}
	if err := s.AddDriverToRace(driverID, race.ID); err != nil {
		return RaceMeta{}, err
	}
	return s.GetRace(race.ID)
}

// GetRace returns the current meta for a race (by value, safe to mutate).
func (s *Service) GetRace(raceID string) (RaceMeta, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	r, ok := s.races[raceID]
	if !ok {
		return RaceMeta{}, ErrRaceNotFound
	}
	return *r, nil
}

// GetDriver returns the current meta for a driver.
func (s *Service) GetDriver(driverID string) (DriverMeta, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	d, ok := s.drivers[driverID]
	if !ok {
		return DriverMeta{}, ErrDriverNotFound
	}
	return *d, nil
}

// ListRaces returns a snapshot copy of all races.
func (s *Service) ListRaces() []RaceMeta {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]RaceMeta, 0, len(s.races))
	for _, r := range s.races {
		out = append(out, *r)
	}
	return out
}

// ListDrivers returns a snapshot copy of all non-offline drivers.
func (s *Service) ListDrivers() []DriverMeta {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]DriverMeta, 0, len(s.drivers))
	for _, d := range s.drivers {
		if d.Status != DriverStatusOffline {
			out = append(out, *d)
		}
	}
	return out
}

// helpers -----------------------------------------------------------------

func removeString(s []string, v string) []string {
	for i, x := range s {
		if x == v {
			return append(s[:i], s[i+1:]...)
		}
	}
	return s
}

func containsString(s []string, v string) bool {
	for _, x := range s {
		if x == v {
			return true
		}
	}
	return false
}

// hashHue returns a stable 0..360 hue for the given string.
func hashHue(s string) int {
	var h uint32 = 5381
	for i := 0; i < len(s); i++ {
		h = h*33 ^ uint32(s[i])
	}
	return int(h % 360)
}

type seqCounter struct{ v atomic.Uint64 }