// Package racenamestub provides the in-process implementation of the
// ports.RaceNameDirectory contract used by unit tests that do not need
// a Redis dependency. The stub enforces the full two-tier Race Name
// Directory invariants (registered, reservation, pending_registration)
// across the lifetime of one process, and is interchangeable with the
// Redis adapter under the same shared behavioural test suite.
package racenamestub

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	"galaxy/lobby/internal/domain/racename"
	"galaxy/lobby/internal/ports"
)

// Directory is the in-memory implementation of ports.RaceNameDirectory.
// The zero value is not usable; callers must construct instances with
// NewDirectory so the underlying data structures and policy are ready.
type Directory struct {
	mu         sync.Mutex
	policy     *racename.Policy
	nowFn      func() time.Time
	registered map[racename.CanonicalKey]*registeredEntry
	entries    map[racename.CanonicalKey]*canonicalEntry
}

// Option tunes Directory construction. Options are evaluated in order.
type Option func(*Directory)

// WithClock overrides the default time.Now clock used to stamp
// reserved_at_ms and registered_at_ms. It is intended for deterministic
// tests.
func WithClock(nowFn func() time.Time) Option {
	return func(directory *Directory) {
		if nowFn != nil {
			directory.nowFn = nowFn
		}
	}
}

// NewDirectory constructs an empty in-memory Race Name Directory backed
// by its own freshly allocated racename.Policy. Returned instances are
// safe for concurrent use.
func NewDirectory(opts ...Option) (*Directory, error) {
	policy, err := racename.NewPolicy()
	if err != nil {
		return nil, fmt.Errorf("new racename stub directory: %w", err)
	}

	directory := &Directory{
		policy:     policy,
		nowFn:      time.Now,
		registered: make(map[racename.CanonicalKey]*registeredEntry),
		entries:    make(map[racename.CanonicalKey]*canonicalEntry),
	}
	for _, opt := range opts {
		opt(directory)
	}

	return directory, nil
}

// registeredEntry models one registered name owned by exactly one user.
type registeredEntry struct {
	userID         string
	raceName       string
	sourceGameID   string
	registeredAtMs int64
}

// canonicalEntry groups the per-game reservations (including
// pending_registration ones) owned by the sole user bound to one
// canonical key.
type canonicalEntry struct {
	holderUserID string
	reservations map[string]*reservationEntry
}

// reservationEntry models one per-game reservation.
type reservationEntry struct {
	raceName         string
	reservedAtMs     int64
	status           string
	eligibleUntilMs  int64
	hasEligibleUntil bool
}

const (
	statusReserved = "reserved"
	statusPending  = "pending_registration"
)

// Canonicalize delegates to the racename policy and returns the
// canonical key as a plain string. Validation failures surface
// ports.ErrInvalidName for compatibility with the Redis adapter.
func (directory *Directory) Canonicalize(raceName string) (string, error) {
	if directory == nil {
		return "", errors.New("canonicalize race name: nil directory")
	}
	canonical, err := directory.policy.Canonicalize(raceName)
	if err != nil {
		return "", fmt.Errorf("canonicalize race name: %w", ports.ErrInvalidName)
	}
	return canonical.String(), nil
}

// Check reports whether raceName is taken for actorUserID.
func (directory *Directory) Check(
	ctx context.Context,
	raceName, actorUserID string,
) (ports.Availability, error) {
	if directory == nil {
		return ports.Availability{}, errors.New("check race name: nil directory")
	}
	if err := checkContext(ctx, "check race name"); err != nil {
		return ports.Availability{}, err
	}
	actor, err := normalizeNonEmpty(actorUserID, "check race name", "actor user id")
	if err != nil {
		return ports.Availability{}, err
	}
	canonical, err := directory.policy.Canonicalize(raceName)
	if err != nil {
		return ports.Availability{}, fmt.Errorf("check race name: %w", ports.ErrInvalidName)
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	if registered, ok := directory.registered[canonical]; ok {
		return ports.Availability{
			Taken:        registered.userID != actor,
			HolderUserID: registered.userID,
			Kind:         ports.KindRegistered,
		}, nil
	}
	entry, ok := directory.entries[canonical]
	if !ok {
		return ports.Availability{}, nil
	}
	kind := kindFromReservations(entry.reservations)
	return ports.Availability{
		Taken:        entry.holderUserID != actor,
		HolderUserID: entry.holderUserID,
		Kind:         kind,
	}, nil
}

// Reserve claims raceName for (gameID, userID) per the port contract.
func (directory *Directory) Reserve(
	ctx context.Context,
	gameID, userID, raceName string,
) error {
	if directory == nil {
		return errors.New("reserve race name: nil directory")
	}
	if err := checkContext(ctx, "reserve race name"); err != nil {
		return err
	}
	game, err := normalizeNonEmpty(gameID, "reserve race name", "game id")
	if err != nil {
		return err
	}
	user, err := normalizeNonEmpty(userID, "reserve race name", "user id")
	if err != nil {
		return err
	}
	displayName, err := racename.ValidateName(raceName)
	if err != nil {
		return fmt.Errorf("reserve race name: %w", ports.ErrInvalidName)
	}
	canonical, err := directory.policy.Canonical(displayName)
	if err != nil {
		return fmt.Errorf("reserve race name: %w", ports.ErrInvalidName)
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	if registered, ok := directory.registered[canonical]; ok && registered.userID != user {
		return ports.ErrNameTaken
	}
	entry, ok := directory.entries[canonical]
	if ok && entry.holderUserID != user {
		return ports.ErrNameTaken
	}
	if !ok {
		entry = &canonicalEntry{
			holderUserID: user,
			reservations: make(map[string]*reservationEntry),
		}
		directory.entries[canonical] = entry
	}
	if _, exists := entry.reservations[game]; exists {
		return nil
	}
	entry.reservations[game] = &reservationEntry{
		raceName:     displayName,
		reservedAtMs: directory.nowFn().UTC().UnixMilli(),
		status:       statusReserved,
	}
	return nil
}

// ReleaseReservation is a defensive no-op in the three cases described
// by the port contract.
func (directory *Directory) ReleaseReservation(
	ctx context.Context,
	gameID, userID, raceName string,
) error {
	if directory == nil {
		return errors.New("release race name reservation: nil directory")
	}
	if err := checkContext(ctx, "release race name reservation"); err != nil {
		return err
	}
	game, err := normalizeNonEmpty(gameID, "release race name reservation", "game id")
	if err != nil {
		return err
	}
	user, err := normalizeNonEmpty(userID, "release race name reservation", "user id")
	if err != nil {
		return err
	}
	canonical, err := directory.policy.Canonicalize(raceName)
	if err != nil {
		return nil
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	entry, ok := directory.entries[canonical]
	if !ok || entry.holderUserID != user {
		return nil
	}
	if _, exists := entry.reservations[game]; !exists {
		return nil
	}
	delete(entry.reservations, game)
	if len(entry.reservations) == 0 {
		delete(directory.entries, canonical)
	}
	return nil
}

// MarkPendingRegistration promotes the reservation held for (gameID,
// userID) on raceName's canonical key to pending_registration status.
func (directory *Directory) MarkPendingRegistration(
	ctx context.Context,
	gameID, userID, raceName string,
	eligibleUntil time.Time,
) error {
	if directory == nil {
		return errors.New("mark pending race name registration: nil directory")
	}
	if err := checkContext(ctx, "mark pending race name registration"); err != nil {
		return err
	}
	game, err := normalizeNonEmpty(gameID, "mark pending race name registration", "game id")
	if err != nil {
		return err
	}
	user, err := normalizeNonEmpty(userID, "mark pending race name registration", "user id")
	if err != nil {
		return err
	}
	if eligibleUntil.IsZero() {
		return fmt.Errorf("mark pending race name registration: eligible until must be set")
	}
	displayName, err := racename.ValidateName(raceName)
	if err != nil {
		return fmt.Errorf("mark pending race name registration: %w", ports.ErrInvalidName)
	}
	canonical, err := directory.policy.Canonical(displayName)
	if err != nil {
		return fmt.Errorf("mark pending race name registration: %w", ports.ErrInvalidName)
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	entry, ok := directory.entries[canonical]
	if !ok || entry.holderUserID != user {
		return fmt.Errorf("mark pending race name registration: reservation missing for game %q user %q", game, user)
	}
	reservation, ok := entry.reservations[game]
	if !ok {
		return fmt.Errorf("mark pending race name registration: reservation missing for game %q user %q", game, user)
	}
	eligibleUntilMs := eligibleUntil.UTC().UnixMilli()
	if reservation.status == statusPending {
		if !reservation.hasEligibleUntil || reservation.eligibleUntilMs != eligibleUntilMs {
			return fmt.Errorf("mark pending race name registration: %w", ports.ErrInvalidName)
		}
		return nil
	}
	reservation.status = statusPending
	reservation.eligibleUntilMs = eligibleUntilMs
	reservation.hasEligibleUntil = true
	reservation.raceName = displayName
	return nil
}

// ExpirePendingRegistrations releases every pending entry whose
// eligibleUntil is at or before now and returns the freed entries.
func (directory *Directory) ExpirePendingRegistrations(
	ctx context.Context,
	now time.Time,
) ([]ports.ExpiredPending, error) {
	if directory == nil {
		return nil, errors.New("expire pending race name registrations: nil directory")
	}
	if err := checkContext(ctx, "expire pending race name registrations"); err != nil {
		return nil, err
	}
	cutoff := now.UTC().UnixMilli()

	directory.mu.Lock()
	defer directory.mu.Unlock()

	var expired []ports.ExpiredPending
	for canonical, entry := range directory.entries {
		for game, reservation := range entry.reservations {
			if reservation.status != statusPending || !reservation.hasEligibleUntil {
				continue
			}
			if reservation.eligibleUntilMs > cutoff {
				continue
			}
			expired = append(expired, ports.ExpiredPending{
				CanonicalKey:    canonical.String(),
				RaceName:        reservation.raceName,
				GameID:          game,
				UserID:          entry.holderUserID,
				EligibleUntilMs: reservation.eligibleUntilMs,
			})
			delete(entry.reservations, game)
		}
		if len(entry.reservations) == 0 {
			delete(directory.entries, canonical)
		}
	}
	return expired, nil
}

// Register converts the pending entry for (gameID, userID) on
// raceName's canonical key into a registered race name.
func (directory *Directory) Register(
	ctx context.Context,
	gameID, userID, raceName string,
) error {
	if directory == nil {
		return errors.New("register race name: nil directory")
	}
	if err := checkContext(ctx, "register race name"); err != nil {
		return err
	}
	game, err := normalizeNonEmpty(gameID, "register race name", "game id")
	if err != nil {
		return err
	}
	user, err := normalizeNonEmpty(userID, "register race name", "user id")
	if err != nil {
		return err
	}
	displayName, err := racename.ValidateName(raceName)
	if err != nil {
		return fmt.Errorf("register race name: %w", ports.ErrInvalidName)
	}
	canonical, err := directory.policy.Canonical(displayName)
	if err != nil {
		return fmt.Errorf("register race name: %w", ports.ErrInvalidName)
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	if existing, ok := directory.registered[canonical]; ok {
		if existing.userID == user {
			return nil
		}
		return ports.ErrNameTaken
	}
	entry, ok := directory.entries[canonical]
	if !ok || entry.holderUserID != user {
		return ports.ErrPendingMissing
	}
	pending, ok := entry.reservations[game]
	if !ok || pending.status != statusPending {
		return ports.ErrPendingMissing
	}
	if !pending.hasEligibleUntil || pending.eligibleUntilMs <= directory.nowFn().UTC().UnixMilli() {
		return ports.ErrPendingExpired
	}

	directory.registered[canonical] = &registeredEntry{
		userID:         user,
		raceName:       displayName,
		sourceGameID:   game,
		registeredAtMs: directory.nowFn().UTC().UnixMilli(),
	}
	delete(entry.reservations, game)
	if len(entry.reservations) == 0 {
		delete(directory.entries, canonical)
	}
	return nil
}

// ListRegistered returns every registered race name owned by userID.
func (directory *Directory) ListRegistered(
	ctx context.Context,
	userID string,
) ([]ports.RegisteredName, error) {
	if directory == nil {
		return nil, errors.New("list registered race names: nil directory")
	}
	if err := checkContext(ctx, "list registered race names"); err != nil {
		return nil, err
	}
	user, err := normalizeNonEmpty(userID, "list registered race names", "user id")
	if err != nil {
		return nil, err
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	var results []ports.RegisteredName
	for canonical, registered := range directory.registered {
		if registered.userID != user {
			continue
		}
		results = append(results, ports.RegisteredName{
			CanonicalKey:   canonical.String(),
			RaceName:       registered.raceName,
			SourceGameID:   registered.sourceGameID,
			RegisteredAtMs: registered.registeredAtMs,
		})
	}
	return results, nil
}

// ListPendingRegistrations returns every pending registration owned by
// userID.
func (directory *Directory) ListPendingRegistrations(
	ctx context.Context,
	userID string,
) ([]ports.PendingRegistration, error) {
	if directory == nil {
		return nil, errors.New("list pending race name registrations: nil directory")
	}
	if err := checkContext(ctx, "list pending race name registrations"); err != nil {
		return nil, err
	}
	user, err := normalizeNonEmpty(userID, "list pending race name registrations", "user id")
	if err != nil {
		return nil, err
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	var results []ports.PendingRegistration
	for canonical, entry := range directory.entries {
		if entry.holderUserID != user {
			continue
		}
		for game, reservation := range entry.reservations {
			if reservation.status != statusPending {
				continue
			}
			results = append(results, ports.PendingRegistration{
				CanonicalKey:    canonical.String(),
				RaceName:        reservation.raceName,
				GameID:          game,
				ReservedAtMs:    reservation.reservedAtMs,
				EligibleUntilMs: reservation.eligibleUntilMs,
			})
		}
	}
	return results, nil
}

// ListReservations returns every active reservation owned by userID
// whose status has not yet been promoted to pending_registration.
func (directory *Directory) ListReservations(
	ctx context.Context,
	userID string,
) ([]ports.Reservation, error) {
	if directory == nil {
		return nil, errors.New("list race name reservations: nil directory")
	}
	if err := checkContext(ctx, "list race name reservations"); err != nil {
		return nil, err
	}
	user, err := normalizeNonEmpty(userID, "list race name reservations", "user id")
	if err != nil {
		return nil, err
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	var results []ports.Reservation
	for canonical, entry := range directory.entries {
		if entry.holderUserID != user {
			continue
		}
		for game, reservation := range entry.reservations {
			if reservation.status != statusReserved {
				continue
			}
			results = append(results, ports.Reservation{
				CanonicalKey: canonical.String(),
				RaceName:     reservation.raceName,
				GameID:       game,
				ReservedAtMs: reservation.reservedAtMs,
			})
		}
	}
	return results, nil
}

// ReleaseAllByUser clears every binding owned by userID atomically
// under the directory mutex.
func (directory *Directory) ReleaseAllByUser(
	ctx context.Context,
	userID string,
) error {
	if directory == nil {
		return errors.New("release all race names by user: nil directory")
	}
	if err := checkContext(ctx, "release all race names by user"); err != nil {
		return err
	}
	user, err := normalizeNonEmpty(userID, "release all race names by user", "user id")
	if err != nil {
		return err
	}

	directory.mu.Lock()
	defer directory.mu.Unlock()

	for canonical, registered := range directory.registered {
		if registered.userID == user {
			delete(directory.registered, canonical)
		}
	}
	for canonical, entry := range directory.entries {
		if entry.holderUserID == user {
			delete(directory.entries, canonical)
		}
	}
	return nil
}

// kindFromReservations returns the strongest ports.Kind constant for a
// canonicalEntry's reservation set (pending_registration beats
// reservation).
func kindFromReservations(reservations map[string]*reservationEntry) string {
	for _, reservation := range reservations {
		if reservation.status == statusPending {
			return ports.KindPendingRegistration
		}
	}
	return ports.KindReservation
}

// checkContext rejects nil or already-canceled contexts so the stub
// surfaces cancellation identically to the Redis adapter.
func checkContext(ctx context.Context, operation string) error {
	if ctx == nil {
		return fmt.Errorf("%s: nil context", operation)
	}
	if err := ctx.Err(); err != nil {
		return fmt.Errorf("%s: %w", operation, err)
	}
	return nil
}

// normalizeNonEmpty trims value and rejects empty results with a
// descriptive error including operation and field names.
func normalizeNonEmpty(value, operation, field string) (string, error) {
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return "", fmt.Errorf("%s: %s must not be empty", operation, field)
	}
	return trimmed, nil
}

// Ensure *Directory satisfies the port interface at compile time.
var _ ports.RaceNameDirectory = (*Directory)(nil)