package service

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
	"time"

	"bugulma/backend/internal/matching/engine"

	"github.com/go-redis/redis/v8"
)

// CacheService provides caching layer for match results
// Based on concept spec: Fast Matching (<100ms) using Redis cache
type CacheService interface {
	GetMatches(ctx context.Context, key string) ([]*engine.Candidate, error)
	SetMatches(ctx context.Context, key string, matches []*engine.Candidate, ttl time.Duration) error
	InvalidateByResourceID(ctx context.Context, resourceID string) error
	InvalidateAll(ctx context.Context) error
}

// MemoryCacheService is an in-memory implementation for development
// In production, use Redis implementation
type MemoryCacheService struct {
	cache map[string]cachedMatches
}

type cachedMatches struct {
	matches   []*engine.Candidate
	expiresAt time.Time
}

// NewMemoryCacheService creates a new in-memory cache service
func NewMemoryCacheService() *MemoryCacheService {
	return &MemoryCacheService{
		cache: make(map[string]cachedMatches),
	}
}

// GetMatches retrieves cached matches
func (c *MemoryCacheService) GetMatches(ctx context.Context, key string) ([]*engine.Candidate, error) {
	cached, exists := c.cache[key]
	if !exists {
		return nil, fmt.Errorf("cache miss")
	}

	if time.Now().After(cached.expiresAt) {
		delete(c.cache, key)
		return nil, fmt.Errorf("cache expired")
	}

	return cached.matches, nil
}

// SetMatches caches match results
func (c *MemoryCacheService) SetMatches(ctx context.Context, key string, matches []*engine.Candidate, ttl time.Duration) error {
	c.cache[key] = cachedMatches{
		matches:   matches,
		expiresAt: time.Now().Add(ttl),
	}
	return nil
}

// InvalidateByResourceID invalidates cache entries containing a specific resource
func (c *MemoryCacheService) InvalidateByResourceID(ctx context.Context, resourceID string) error {
	// Simple implementation: clear entire cache
	// In production, maintain resource-to-cache-key mappings
	c.cache = make(map[string]cachedMatches)
	return nil
}

// InvalidateAll clears entire cache
func (c *MemoryCacheService) InvalidateAll(ctx context.Context) error {
	c.cache = make(map[string]cachedMatches)
	return nil
}

// GenerateCacheKey generates a cache key for match queries
func GenerateCacheKey(resourceType string, lat, lng, maxDistanceKm float64) string {
	return fmt.Sprintf("matches:%s:%.4f:%.4f:%.1f", resourceType, lat, lng, maxDistanceKm)
}

// RedisCacheService is a Redis-backed cache implementation for production use
type RedisCacheService struct {
	client *redis.Client
}

// NewRedisCacheService creates a new Redis cache service
func NewRedisCacheService(redisURL string) (*RedisCacheService, error) {
	opt, err := redis.ParseURL(redisURL)
	if err != nil {
		return nil, fmt.Errorf("failed to parse Redis URL: %w", err)
	}

	client := redis.NewClient(opt)

	// Test connection
	ctx := context.Background()
	if err := client.Ping(ctx).Err(); err != nil {
		return nil, fmt.Errorf("failed to connect to Redis: %w", err)
	}

	return &RedisCacheService{
		client: client,
	}, nil
}

// GetMatches retrieves cached matches from Redis
func (r *RedisCacheService) GetMatches(ctx context.Context, key string) ([]*engine.Candidate, error) {
	val, err := r.client.Get(ctx, key).Result()
	if err == redis.Nil {
		return nil, fmt.Errorf("cache miss")
	}
	if err != nil {
		return nil, fmt.Errorf("failed to get cache key %s: %w", key, err)
	}

	var matches []*engine.Candidate
	if err := json.Unmarshal([]byte(val), &matches); err != nil {
		return nil, fmt.Errorf("failed to unmarshal cached data: %w", err)
	}

	return matches, nil
}

// SetMatches caches match results in Redis with TTL
func (r *RedisCacheService) SetMatches(ctx context.Context, key string, matches []*engine.Candidate, ttl time.Duration) error {
	data, err := json.Marshal(matches)
	if err != nil {
		return fmt.Errorf("failed to marshal matches: %w", err)
	}

	if err := r.client.Set(ctx, key, data, ttl).Err(); err != nil {
		return fmt.Errorf("failed to set cache key %s: %w", key, err)
	}

	return nil
}

// InvalidateByResourceID invalidates cache entries containing a specific resource
// Uses Redis SCAN to efficiently find and delete matching keys
func (r *RedisCacheService) InvalidateByResourceID(ctx context.Context, resourceID string) error {
	// Use SCAN to find all cache entries containing this resource ID
	// Pattern: matches:resourceType:resourceID:lat:lng:distance
	pattern := fmt.Sprintf("*%s*", resourceID)

	var cursor uint64
	var keys []string
	var err error

	// SCAN with pattern to find matching keys
	for {
		keys, cursor, err = r.client.Scan(ctx, cursor, pattern, 100).Result()
		if err != nil {
			return fmt.Errorf("failed to scan cache keys: %w", err)
		}

		// Filter keys that actually contain the resource ID in match context
		var keysToDelete []string
		for _, key := range keys {
			if strings.Contains(key, resourceID) {
				keysToDelete = append(keysToDelete, key)
			}
		}

		// Delete found keys
		if len(keysToDelete) > 0 {
			if err := r.client.Del(ctx, keysToDelete...).Err(); err != nil {
				return fmt.Errorf("failed to delete cache keys: %w", err)
			}
		}

		if cursor == 0 {
			break
		}
	}

	return nil
}

// InvalidateAll clears entire cache database
func (r *RedisCacheService) InvalidateAll(ctx context.Context) error {
	if err := r.client.FlushDB(ctx).Err(); err != nil {
		return fmt.Errorf("failed to flush Redis database: %w", err)
	}
	return nil
}

// Close closes the Redis connection
func (r *RedisCacheService) Close() error {
	return r.client.Close()
}