package catalog

import (
	"context"
	"errors"
	"fmt"
	"math"
	"strings"
	"time"
)

// Errors returned by the catalog service.
var (
	ErrNotFound        = errors.New("not found")
	ErrAlreadyExists   = errors.New("already exists")
	ErrInvalidInput    = errors.New("invalid input")
	ErrImmutableSystem = errors.New("system resources are immutable")
	ErrStoreMissing    = errors.New("catalog: store not configured")
)

// Validation bounds for the user's setup:
//   - largest room 4.46 m × 3.19 m → tracks ≤ 4.5 m × 3.2 m bounding box
//   - car scale 1/27 → car length 50..200 mm (typical 1/27 touring envelope)
//   - 3D-printer Bambu A1 build volume → 220×220×250 mm
const (
	maxTrackLengthM = 4.5
	maxTrackWidthM  = 3.2
	maxLaneWidthM   = 1.0
	minCarLengthMm  = 40.0
	maxCarLengthMm  = 260.0 // 1/24 F1 ≈ 238 мм
	minCarWidthMm   = 20.0
	maxCarWidthMm   = 120.0
)

// CreateTrackOptions are the inputs for CreateTrack.
type CreateTrackOptions struct {
	ID          string     // optional; auto-generated if empty
	Name        string     // required
	Description string     // optional
	AuthorID    string     // optional; defaults to "system"
	Visibility  Visibility // optional; defaults to VisibilityPublic
	Scale       int        // optional; defaults to 27
	LengthM     float64    // optional; computed from centerline if 0
	WidthM      float64    // optional; computed from centerline if 0
	LaneWidthM  float64    // optional; defaults to 0.20
	Surface     Surface    // optional; defaults to carpet
	Tags        []string   // optional
	Centerline  []Waypoint // optional; defaults to a parametric oval
}

// Validate returns an error if opts is incomplete.
func (o CreateTrackOptions) Validate() error {
	if strings.TrimSpace(o.Name) == "" {
		return fmt.Errorf("%w: name required", ErrInvalidInput)
	}
	if o.LengthM < 0 || o.LengthM > maxTrackLengthM {
		return fmt.Errorf("%w: length_m must be in [0, %.1f]", ErrInvalidInput, maxTrackLengthM)
	}
	if o.WidthM < 0 || o.WidthM > maxTrackWidthM {
		return fmt.Errorf("%w: width_m must be in [0, %.1f]", ErrInvalidInput, maxTrackWidthM)
	}
	if o.LaneWidthM < 0 || o.LaneWidthM > maxLaneWidthM {
		return fmt.Errorf("%w: lane_width_m must be in [0, %.1f]", ErrInvalidInput, maxLaneWidthM)
	}
	if o.Visibility == VisibilitySystem {
		return fmt.Errorf("%w: cannot create system track via API", ErrInvalidInput)
	}
	return nil
}

// CreateTrack inserts a new user-authored track.
func (s *Service) CreateTrack(ctx context.Context, opts CreateTrackOptions) (TrackMeta, error) {
	if err := opts.Validate(); err != nil {
		return TrackMeta{}, err
	}
	id := opts.ID
	if id == "" {
		id = slugify(opts.Name)
	}
	vis := opts.Visibility
	if vis == "" {
		vis = VisibilityPublic
	}
	auth := opts.AuthorID
	if auth == "" {
		auth = AuthorSystem
	}
	scale := opts.Scale
	if scale == 0 {
		scale = 27
	}
	sfc := opts.Surface
	if sfc == "" {
		sfc = SurfaceCarpet
	}

	if _, exists := s.getTrackLocked(id); exists {
		return TrackMeta{}, fmt.Errorf("%w: track %q", ErrAlreadyExists, id)
	}

	now := time.Now().UnixMilli()
	t := TrackMeta{
		ID:          id,
		Name:        strings.TrimSpace(opts.Name),
		Description: opts.Description,
		AuthorID:    auth,
		Visibility:  vis,
		Scale:       scale,
		LengthM:     opts.LengthM,
		WidthM:      opts.WidthM,
		LaneWidthM:  opts.LaneWidthM,
		Surface:     sfc,
		Tags:        append([]string(nil), opts.Tags...),
		Centerline:  append([]Waypoint(nil), opts.Centerline...),
		CreatedMs:   now,
		UpdatedMs:   now,
	}
	s.normalizeTrack(&t)

	if t.Bounds.MaxX > maxTrackLengthM || t.Bounds.MaxY > maxTrackWidthM {
		return TrackMeta{}, fmt.Errorf("%w: track too large for 446x319 cm room (got %.2fx%.2f m)",
			ErrInvalidInput, t.Bounds.MaxX, t.Bounds.MaxY)
	}

	if err := s.persistUpsertTrack(ctx, t); err != nil {
		return TrackMeta{}, err
	}
	return t, nil
}

// UpdateTrackOptions carries the patch fields for UpdateTrack.
type UpdateTrackOptions struct {
	Name        *string
	Description *string
	Visibility  *Visibility
	LengthM     *float64
	WidthM      *float64
	LaneWidthM  *float64
	Surface     *Surface
	Tags        *[]string
	Centerline  *[]Waypoint
}

// UpdateTrack applies a partial update to an existing track.
func (s *Service) UpdateTrack(ctx context.Context, id string, opts UpdateTrackOptions) (TrackMeta, error) {
	s.mu.Lock()
	t, ok := s.tracks[id]
	if !ok {
		s.mu.Unlock()
		return TrackMeta{}, fmt.Errorf("%w: track %q", ErrNotFound, id)
	}
	if t.Visibility == VisibilitySystem {
		s.mu.Unlock()
		return TrackMeta{}, fmt.Errorf("%w: track %q", ErrImmutableSystem, id)
	}

	if opts.Name != nil {
		t.Name = strings.TrimSpace(*opts.Name)
	}
	if opts.Description != nil {
		t.Description = *opts.Description
	}
	if opts.Visibility != nil {
		if *opts.Visibility == VisibilitySystem {
			s.mu.Unlock()
			return TrackMeta{}, fmt.Errorf("%w: cannot promote to system", ErrInvalidInput)
		}
		t.Visibility = *opts.Visibility
	}
	if opts.LengthM != nil {
		t.LengthM = *opts.LengthM
	}
	if opts.WidthM != nil {
		t.WidthM = *opts.WidthM
	}
	if opts.LaneWidthM != nil {
		t.LaneWidthM = *opts.LaneWidthM
	}
	if opts.Surface != nil {
		t.Surface = *opts.Surface
	}
	if opts.Tags != nil {
		t.Tags = append([]string(nil), *opts.Tags...)
	}
	if opts.Centerline != nil {
		t.Centerline = append([]Waypoint(nil), *opts.Centerline...)
		t.Bounds = computeBounds(t.Centerline)
		t.LengthM = t.Bounds.LengthM
		t.WidthM = t.Bounds.WidthM
	} else {
		t.Bounds = computeBounds(t.Centerline)
	}
	t.UpdatedMs = time.Now().UnixMilli()

	if t.Bounds.MaxX > maxTrackLengthM || t.Bounds.MaxY > maxTrackWidthM {
		s.mu.Unlock()
		return TrackMeta{}, fmt.Errorf("%w: track too large (got %.2fx%.2f m)",
			ErrInvalidInput, t.Bounds.MaxX, t.Bounds.MaxY)
	}

	updated := *t
	s.mu.Unlock()

	if err := s.persistUpsertTrack(ctx, updated); err != nil {
		return TrackMeta{}, err
	}
	return updated, nil
}

// DeleteTrack removes a track by ID. System tracks are immutable.
func (s *Service) DeleteTrack(ctx context.Context, id string) error {
	s.mu.RLock()
	t, ok := s.tracks[id]
	s.mu.RUnlock()
	if !ok {
		return fmt.Errorf("%w: track %q", ErrNotFound, id)
	}
	if t.Visibility == VisibilitySystem {
		return fmt.Errorf("%w: track %q", ErrImmutableSystem, id)
	}
	return s.persistDeleteTrack(ctx, id)
}

// -------------------------------------------------------------------------
// Cars
// -------------------------------------------------------------------------

// CreateCarOptions are the inputs for CreateCar.
type CreateCarOptions struct {
	ID         string
	Name       string
	OwnerID    string
	Visibility Visibility
	Scale      int

	LengthMm float64
	WidthMm  float64
	HeightMm float64
	WeightG  float64

	Chassis ChassisSpec
	Motor   MotorSpec
	Battery BatterySpec
	Drive   Drivetrain

	TopSpeedMs float64
	ColorHex   string
	AvatarURL  string
	Active     *bool // optional; defaults to true
}

// Validate sanity-checks dimensions and required fields.
func (o CreateCarOptions) Validate() error {
	if strings.TrimSpace(o.Name) == "" {
		return fmt.Errorf("%w: name required", ErrInvalidInput)
	}
	if o.LengthMm < minCarLengthMm || o.LengthMm > maxCarLengthMm {
		return fmt.Errorf("%w: length_mm must be in [%.0f, %.0f]", ErrInvalidInput, minCarLengthMm, maxCarLengthMm)
	}
	if o.WidthMm < minCarWidthMm || o.WidthMm > maxCarWidthMm {
		return fmt.Errorf("%w: width_mm must be in [%.0f, %.0f]", ErrInvalidInput, minCarWidthMm, maxCarWidthMm)
	}
	if o.Visibility == VisibilitySystem {
		return fmt.Errorf("%w: cannot create system car via API", ErrInvalidInput)
	}
	return nil
}

// CreateCar inserts a new car.
func (s *Service) CreateCar(ctx context.Context, opts CreateCarOptions) (CarMeta, error) {
	if err := opts.Validate(); err != nil {
		return CarMeta{}, err
	}
	id := opts.ID
	if id == "" {
		id = slugify(opts.Name)
	}
	vis := opts.Visibility
	if vis == "" {
		vis = VisibilityPublic
	}
	owner := opts.OwnerID
	if owner == "" {
		owner = AuthorSystem
	}
	scale := opts.Scale
	if scale == 0 {
		scale = 27
	}
	drive := opts.Drive
	if drive == "" {
		drive = Drivetrain2WD
	}
	active := true
	if opts.Active != nil {
		active = *opts.Active
	}

	if _, exists := s.getCarLocked(id); exists {
		return CarMeta{}, fmt.Errorf("%w: car %q", ErrAlreadyExists, id)
	}

	now := time.Now().UnixMilli()
	c := CarMeta{
		ID:         id,
		Name:       strings.TrimSpace(opts.Name),
		OwnerID:    owner,
		Visibility: vis,
		Scale:      scale,
		LengthMm:   opts.LengthMm,
		WidthMm:    opts.WidthMm,
		HeightMm:   opts.HeightMm,
		WeightG:    opts.WeightG,
		Chassis:    opts.Chassis,
		Motor:      opts.Motor,
		Battery:    opts.Battery,
		Drive:      drive,
		TopSpeedMs: opts.TopSpeedMs,
		ColorHex:   opts.ColorHex,
		AvatarURL:  opts.AvatarURL,
		Active:     active,
		CreatedMs:  now,
		UpdatedMs:  now,
	}
	s.normalizeCar(&c)

	if err := s.persistUpsertCar(ctx, c); err != nil {
		return CarMeta{}, err
	}
	return c, nil
}

// UpdateCarOptions is the patch for UpdateCar.
type UpdateCarOptions struct {
	Name       *string
	Visibility *Visibility
	LengthMm   *float64
	WidthMm    *float64
	HeightMm   *float64
	WeightG    *float64
	TopSpeedMs *float64
	ColorHex   *string
	Active     *bool
	Chassis    *ChassisSpec
	Motor      *MotorSpec
	Battery    *BatterySpec
	Drive      *Drivetrain
}

// UpdateCar applies a partial update.
func (s *Service) UpdateCar(ctx context.Context, id string, opts UpdateCarOptions) (CarMeta, error) {
	s.mu.Lock()
	c, ok := s.cars[id]
	if !ok {
		s.mu.Unlock()
		return CarMeta{}, fmt.Errorf("%w: car %q", ErrNotFound, id)
	}
	if c.Visibility == VisibilitySystem {
		s.mu.Unlock()
		return CarMeta{}, fmt.Errorf("%w: car %q", ErrImmutableSystem, id)
	}

	if opts.Name != nil {
		c.Name = strings.TrimSpace(*opts.Name)
	}
	if opts.Visibility != nil {
		if *opts.Visibility == VisibilitySystem {
			s.mu.Unlock()
			return CarMeta{}, fmt.Errorf("%w: cannot promote to system", ErrInvalidInput)
		}
		c.Visibility = *opts.Visibility
	}
	if opts.LengthMm != nil {
		c.LengthMm = *opts.LengthMm
	}
	if opts.WidthMm != nil {
		c.WidthMm = *opts.WidthMm
	}
	if opts.HeightMm != nil {
		c.HeightMm = *opts.HeightMm
	}
	if opts.WeightG != nil {
		c.WeightG = *opts.WeightG
	}
	if opts.TopSpeedMs != nil {
		c.TopSpeedMs = *opts.TopSpeedMs
	}
	if opts.ColorHex != nil {
		c.ColorHex = *opts.ColorHex
	}
	if opts.Active != nil {
		c.Active = *opts.Active
	}
	if opts.Chassis != nil {
		c.Chassis = *opts.Chassis
	}
	if opts.Motor != nil {
		c.Motor = *opts.Motor
	}
	if opts.Battery != nil {
		c.Battery = *opts.Battery
	}
	if opts.Drive != nil {
		c.Drive = *opts.Drive
	}
	c.UpdatedMs = time.Now().UnixMilli()

	if c.LengthMm < minCarLengthMm || c.LengthMm > maxCarLengthMm ||
		c.WidthMm < minCarWidthMm || c.WidthMm > maxCarWidthMm {
		s.mu.Unlock()
		return CarMeta{}, fmt.Errorf("%w: dimensions out of range", ErrInvalidInput)
	}

	updated := *c
	s.mu.Unlock()

	if err := s.persistUpsertCar(ctx, updated); err != nil {
		return CarMeta{}, err
	}
	return updated, nil
}

// DeleteCar removes a car by id.
func (s *Service) DeleteCar(ctx context.Context, id string) error {
	s.mu.RLock()
	c, ok := s.cars[id]
	s.mu.RUnlock()
	if !ok {
		return fmt.Errorf("%w: car %q", ErrNotFound, id)
	}
	if c.Visibility == VisibilitySystem {
		return fmt.Errorf("%w: car %q", ErrImmutableSystem, id)
	}
	return s.persistDeleteCar(ctx, id)
}

// SetCarStats mutates the read-mostly counters on a car (called by the
// race engine via catalog hooks). Only updates non-zero inputs.
func (s *Service) SetCarStats(ctx context.Context, id string, fn func(*CarMeta)) error {
	s.mu.Lock()
	c, ok := s.cars[id]
	if !ok {
		s.mu.Unlock()
		return fmt.Errorf("%w: car %q", ErrNotFound, id)
	}
	fn(c)
	c.UpdatedMs = time.Now().UnixMilli()
	updated := *c
	s.mu.Unlock()

	if s.store != nil {
		if err := s.store.UpdateCarStats(ctx, id, func(c *CarMeta) {
			fn(c)
			c.UpdatedMs = updated.UpdatedMs
		}); err != nil {
			return err
		}
	}
	s.bump(Event{Kind: EventCarUpsert, CarID: id})
	return nil
}

// -------------------------------------------------------------------------
// Helpers
// -------------------------------------------------------------------------

// getTrackLocked returns a shallow copy of a track from the cache.
// MUST be called with s.mu held.
func (s *Service) getTrackLocked(id string) (TrackMeta, bool) {
	t, ok := s.tracks[id]
	if !ok {
		return TrackMeta{}, false
	}
	return *t, true
}

func (s *Service) getCarLocked(id string) (CarMeta, bool) {
	c, ok := s.cars[id]
	if !ok {
		return CarMeta{}, false
	}
	return *c, true
}

// slugify turns "Sunset Sprint" into "sunset-sprint".
func slugify(s string) string {
	s = strings.ToLower(strings.TrimSpace(s))
	var b strings.Builder
	prevDash := false
	for _, r := range s {
		switch {
		case (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9'):
			b.WriteRune(r)
			prevDash = false
		default:
			if !prevDash && b.Len() > 0 {
				b.WriteRune('-')
				prevDash = true
			}
		}
	}
	out := strings.TrimRight(b.String(), "-")
	if out == "" {
		out = fmt.Sprintf("item-%d", time.Now().UnixNano()%1_000_000)
	}
	return out
}

// computeBounds derives a Bounds from a closed loop of waypoints.
func computeBounds(loop []Waypoint) Bounds {
	if len(loop) == 0 {
		return Bounds{}
	}
	b := Bounds{
		MinX: loop[0].X,
		MinY: loop[0].Y,
		MaxX: loop[0].X,
		MaxY: loop[0].Y,
	}
	for _, p := range loop[1:] {
		if p.X < b.MinX {
			b.MinX = p.X
		}
		if p.Y < b.MinY {
			b.MinY = p.Y
		}
		if p.X > b.MaxX {
			b.MaxX = p.X
		}
		if p.Y > b.MaxY {
			b.MaxY = p.Y
		}
	}
	b.LengthM = b.MaxX - b.MinX
	b.WidthM = b.MaxY - b.MinY
	return b
}

// defaultCenterline generates a parametric oval centered in a box of
// size length_m × width_m. Used when the caller doesn't supply waypoints.
func defaultCenterline(lengthM, widthM float64) []Waypoint {
	if lengthM <= 0 {
		lengthM = 2.0
	}
	if widthM <= 0 {
		widthM = 1.2
	}
	const samples = 24
	cx, cy := lengthM/2, widthM/2
	rx, ry := lengthM*0.45, widthM*0.45
	pts := make([]Waypoint, samples)
	for i := 0; i < samples; i++ {
		t := float64(i) / float64(samples) * 2 * math.Pi
		x := cx + rx*math.Cos(t)
		y := cy + ry*math.Sin(t)
		// Tangent: perpendicular to the radius.
		heading := t + math.Pi/2
		// Curvature: 1/r at this point (approximation using ellipse radii).
		r := math.Sqrt(rx*rx*math.Sin(t)*math.Sin(t) + ry*ry*math.Cos(t)*math.Cos(t))
		curv := 0.0
		if r > 0 {
			curv = math.Min(rx, ry) / (r * r)
		}
		// Speed: slower on tight curves.
		speed := 4.0 - 2.0*math.Min(curv*5, 1)
		pts[i] = Waypoint{X: x, Y: y, HeadingRad: heading, SpeedMs: speed, Curvature: curv}
	}
	return pts
}

// -------------------------------------------------------------------------
// Read APIs (Get / List / Snapshot / Stats)
// -------------------------------------------------------------------------

// ListTracksByVisibility returns tracks matching the given visibility.
func (s *Service) ListTracksByVisibility(v Visibility) []TrackMeta {
	all := s.ListTracks()
	out := all[:0:0]
	for _, t := range all {
		if t.Visibility == v {
			out = append(out, t)
		}
	}
	return out
}

// ListCarsByVisibility returns cars matching the given visibility.
func (s *Service) ListCarsByVisibility(v Visibility) []CarMeta {
	all := s.ListCars()
	out := all[:0:0]
	for _, c := range all {
		if c.Visibility == v {
			out = append(out, c)
		}
	}
	return out
}

// ListCarsByOwner returns cars owned by the given driver ID.
func (s *Service) ListCarsByOwner(ownerID string) []CarMeta {
	all := s.ListCars()
	out := all[:0:0]
	for _, c := range all {
		if c.OwnerID == ownerID {
			out = append(out, c)
		}
	}
	return out
}