package service

import (
	"bugulma/backend/internal/domain"
	"context"
	"crypto/md5"
	"fmt"
	"strings"
	"sync"
	"time"
)

// TranslationCacheEntry represents a cached translation
type TranslationCacheEntry struct {
	EntityType   string
	Field        string
	TargetLocale string
	RussianText  string
	Translated   string
	UseCount     int
	LastUsed     int64
}

// TranslationCacheService manages translation caching and reuse
type TranslationCacheService struct {
	cache      map[string]*TranslationCacheEntry
	locRepo    domain.LocalizationRepository
	locService domain.LocalizationService
	mutex      sync.RWMutex
	maxSize    int
}

// NewTranslationCacheService creates a new translation cache service
func NewTranslationCacheService(locRepo domain.LocalizationRepository, locService domain.LocalizationService) *TranslationCacheService {
	return &TranslationCacheService{
		cache:      make(map[string]*TranslationCacheEntry),
		locRepo:    locRepo,
		locService: locService,
		maxSize:    10000, // Configurable cache size
	}
}

// FindCachedTranslation finds a cached translation for the given parameters
// Returns (translation, found, error) for consistency with TranslationCache API
func (s *TranslationCacheService) FindCachedTranslation(ctx context.Context, entityType, field, targetLocale, russianText string) (string, bool, error) {
	if russianText == "" {
		return "", false, nil
	}

	s.mutex.RLock()
	key := s.generateCacheKey(entityType, field, targetLocale, russianText)
	if entry, exists := s.cache[key]; exists {
		entry.UseCount++
		entry.LastUsed = time.Now().Unix()
		s.mutex.RUnlock()
		return entry.Translated, true, nil
	}
	s.mutex.RUnlock()

	// Try to find in database (slower but persistent)
	if translation := s.findInDatabase(ctx, entityType, field, targetLocale, russianText); translation != "" {
		// Add to cache
		s.AddToCache(entityType, field, targetLocale, russianText, translation)
		return translation, true, nil
	}

	return "", false, nil
}

// FindCachedTranslationLegacy is the legacy API for backward compatibility
// Deprecated: Use FindCachedTranslation with context instead
func (s *TranslationCacheService) FindCachedTranslationLegacy(entityType, field, targetLocale, russianText string) string {
	ctx := context.Background()
	translation, found, _ := s.FindCachedTranslation(ctx, entityType, field, targetLocale, russianText)
	if found {
		return translation
	}
	return ""
}

// AddToCache adds a translation to the cache
func (s *TranslationCacheService) AddToCache(entityType, field, targetLocale, russianText, translated string) {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	s.addToCache(entityType, field, targetLocale, russianText, translated)
}

// addToCache internal method to add to cache (assumes mutex is held)
func (s *TranslationCacheService) addToCache(entityType, field, targetLocale, russianText, translated string) {
	key := s.generateCacheKey(entityType, field, targetLocale, russianText)
	entry := &TranslationCacheEntry{
		EntityType:   entityType,
		Field:        field,
		TargetLocale: targetLocale,
		RussianText:  russianText,
		Translated:   translated,
		UseCount:     1,
		LastUsed:     time.Now().Unix(),
	}

	// Evict least recently used if cache is full
	if len(s.cache) >= s.maxSize {
		s.evictLRU()
	}

	s.cache[key] = entry
}

// findInDatabase searches the database for existing translations of the same Russian text
func (s *TranslationCacheService) findInDatabase(ctx context.Context, entityType, field, targetLocale, russianText string) string {
	if russianText == "" {
		return ""
	}

	normalized := strings.TrimSpace(russianText)
	if normalized == "" {
		return ""
	}

	// Search for localizations with matching Russian source text
	localizations, err := s.locRepo.SearchLocalizations(ctx, normalized, "ru", 10)
	if err != nil {
		return ""
	}

	// Find a matching Russian localization and check if it has a target locale translation
	for _, loc := range localizations {
		if loc.EntityType == entityType && loc.Field == field && loc.Value == normalized {
			// Found matching Russian text, now check for target locale translation
			targetLoc, err := s.locRepo.GetByEntityAndField(ctx, loc.EntityType, loc.EntityID, loc.Field, targetLocale)
			if err == nil && targetLoc != nil && targetLoc.Value != "" {
				return targetLoc.Value
			}
		}
	}

	return ""
}

// generateCacheKey generates a unique key for cache entries
func (s *TranslationCacheService) generateCacheKey(entityType, field, targetLocale, russianText string) string {
	// Create a hash of the Russian text to handle long texts
	textHash := fmt.Sprintf("%x", md5.Sum([]byte(russianText)))
	return fmt.Sprintf("%s:%s:%s:%s", entityType, field, targetLocale, textHash)
}

// evictLRU evicts the least recently used entry from the cache
func (s *TranslationCacheService) evictLRU() {
	var oldestKey string
	var oldestTime int64 = -1

	for key, entry := range s.cache {
		if oldestTime == -1 || entry.LastUsed < oldestTime {
			oldestTime = entry.LastUsed
			oldestKey = key
		}
	}

	if oldestKey != "" {
		delete(s.cache, oldestKey)
	}
}

// GetCacheStats returns statistics about the cache
func (s *TranslationCacheService) GetCacheStats() map[string]interface{} {
	s.mutex.RLock()
	defer s.mutex.RUnlock()

	totalEntries := len(s.cache)
	totalUses := 0
	avgUses := 0.0

	if totalEntries > 0 {
		for _, entry := range s.cache {
			totalUses += entry.UseCount
		}
		avgUses = float64(totalUses) / float64(totalEntries)
	}

	return map[string]interface{}{
		"total_entries": totalEntries,
		"max_size":      s.maxSize,
		"total_uses":    totalUses,
		"avg_uses":      avgUses,
		"utilization":   float64(totalEntries) / float64(s.maxSize) * 100,
	}
}

// ClearCache clears all entries from the cache
func (s *TranslationCacheService) ClearCache() {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	s.cache = make(map[string]*TranslationCacheEntry)
}

// PreloadCache preloads the cache with commonly used translations
func (s *TranslationCacheService) PreloadCache(ctx context.Context, entityType, field, targetLocale string) error {
	if ctx == nil {
		ctx = context.Background()
	}

	// Get translation reuse candidates (Russian text that appears in multiple entities)
	candidates, err := s.locRepo.GetTranslationReuseCandidates(ctx, entityType, field, "ru")
	if err != nil {
		return fmt.Errorf("failed to get reuse candidates: %w", err)
	}

	// For each candidate, find existing translations and cache them
	for _, candidate := range candidates {
		// Find any translation of this Russian text to the target locale
		localizations, err := s.locRepo.SearchLocalizations(ctx, candidate.RussianValue, targetLocale, 1)
		if err != nil || len(localizations) == 0 {
			continue
		}

		// Use the first matching translation
		translation := localizations[0].Value
		if translation != "" {
			s.AddToCache(entityType, field, targetLocale, candidate.RussianValue, translation)
		}
	}

	return nil
}