package auth

import (
	"context"
	"fmt"
	"sync"
	"time"

	"github.com/redis/go-redis/v9"

	"github.com/gochat/gochat/internal/config"
)

// Reference: P2E §1.4 — Refresh Token storage in Redis for rotation tracking
// Refresh tokens are stored in Redis with TTL matching their JWT expiry.
// This enables: token rotation, revocation, and audit trail.

// RefreshTokenStore manages refresh token storage in Redis.
type RefreshTokenStore struct {
	rdb *redis.Client
	cfg *config.JWTConfig
	mu  sync.RWMutex
	mem map[uint]string
}

// NewRefreshTokenStore creates a refresh token store backed by Redis.
func NewRefreshTokenStore(rdb *redis.Client, cfg *config.JWTConfig) *RefreshTokenStore {
	return &RefreshTokenStore{rdb: rdb, cfg: cfg, mem: map[uint]string{}}
}

// Store saves a refresh token in Redis with TTL.
// Key pattern: refresh_token:{user_id}:{token_hash}
func (s *RefreshTokenStore) Store(ctx context.Context, userID uint, refreshToken string) error {
	if s.rdb == nil {
		s.mu.Lock()
		defer s.mu.Unlock()
		s.mem[userID] = refreshToken
		return nil
	}
	key := fmt.Sprintf("gochat:refresh_token:%d", userID)
	ttl := time.Duration(s.cfg.RefreshExpiryHours) * time.Hour
	return s.rdb.Set(ctx, key, refreshToken, ttl).Err()
}

// Validate checks if a refresh token exists and matches the stored value.
func (s *RefreshTokenStore) Validate(ctx context.Context, userID uint, refreshToken string) (bool, error) {
	if s.rdb == nil {
		s.mu.RLock()
		defer s.mu.RUnlock()
		stored, ok := s.mem[userID]
		return ok && stored == refreshToken, nil
	}
	key := fmt.Sprintf("gochat:refresh_token:%d", userID)
	stored, err := s.rdb.Get(ctx, key).Result()
	if err == redis.Nil {
		return false, nil // token not found (expired or revoked)
	}
	if err != nil {
		return false, fmt.Errorf("redis error: %w", err)
	}
	return stored == refreshToken, nil
}

// Revoke removes a refresh token from Redis (logout).
func (s *RefreshTokenStore) Revoke(ctx context.Context, userID uint) error {
	if s.rdb == nil {
		s.mu.Lock()
		defer s.mu.Unlock()
		delete(s.mem, userID)
		return nil
	}
	key := fmt.Sprintf("gochat:refresh_token:%d", userID)
	return s.rdb.Del(ctx, key).Err()
}

// Rotate replaces an old refresh token with a new one (refresh token rotation).
// This ensures each refresh token can only be used once.
func (s *RefreshTokenStore) Rotate(ctx context.Context, userID uint, newRefreshToken string) error {
	return s.Store(ctx, userID, newRefreshToken)
}