package storage

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

	badger "github.com/dgraph-io/badger/v4"

	"kvs/auth"
	"kvs/types"
)

// RevisionService handles revision history management
type RevisionService struct {
	storage *StorageService
}

// NewRevisionService creates a new revision service
func NewRevisionService(storage *StorageService) *RevisionService {
	return &RevisionService{
		storage: storage,
	}
}

// GetRevisionKey generates the storage key for a specific revision
func GetRevisionKey(baseKey string, revision int) string {
	return fmt.Sprintf("%s:rev:%d", baseKey, revision)
}

// StoreRevisionHistory stores a value and manages revision history (up to 3 revisions)
func (r *RevisionService) StoreRevisionHistory(txn *badger.Txn, key string, storedValue types.StoredValue, ttl time.Duration) error {
	// Get existing metadata to check current revisions
	metadataKey := auth.ResourceMetadataKey(key)
	
	var metadata types.ResourceMetadata
	var currentRevisions []int
	
	// Try to get existing metadata
	metadataData, err := r.storage.RetrieveWithDecompression(txn, []byte(metadataKey))
	if err == badger.ErrKeyNotFound {
		// No existing metadata, this is a new key
		metadata = types.ResourceMetadata{
			OwnerUUID:   "", // Will be set by caller if needed
			GroupUUID:   "",
			Permissions: types.DefaultPermissions,
			TTL:         "",
			CreatedAt:   time.Now().Unix(),
			UpdatedAt:   time.Now().Unix(),
		}
		currentRevisions = []int{}
	} else if err != nil {
		// Error reading metadata
		return fmt.Errorf("failed to read metadata: %v", err)
	} else {
		// Parse existing metadata
		err = json.Unmarshal(metadataData, &metadata)
		if err != nil {
			return fmt.Errorf("failed to unmarshal metadata: %v", err)
		}
		
		// Extract current revisions (we store them as a custom field)
		if metadata.TTL == "" {
			currentRevisions = []int{}
		} else {
			// For now, we'll manage revisions separately - let's create a new metadata field
			currentRevisions = []int{1, 2, 3} // Assume all revisions exist for existing keys
		}
	}
	
	// Revision rotation logic: shift existing revisions
	if len(currentRevisions) >= 3 {
		// Delete oldest revision (rev:3)
		oldestRevKey := GetRevisionKey(key, 3)
		txn.Delete([]byte(oldestRevKey))
		
		// Shift rev:2 → rev:3
		rev2Key := GetRevisionKey(key, 2)
		rev2Data, err := r.storage.RetrieveWithDecompression(txn, []byte(rev2Key))
		if err == nil {
			rev3Key := GetRevisionKey(key, 3)
			r.storage.StoreWithTTL(txn, []byte(rev3Key), rev2Data, ttl)
		}
		
		// Shift rev:1 → rev:2  
		rev1Key := GetRevisionKey(key, 1)
		rev1Data, err := r.storage.RetrieveWithDecompression(txn, []byte(rev1Key))
		if err == nil {
			rev2Key := GetRevisionKey(key, 2)
			r.storage.StoreWithTTL(txn, []byte(rev2Key), rev1Data, ttl)
		}
	}
	
	// Store current value as rev:1
	currentValueBytes, err := json.Marshal(storedValue)
	if err != nil {
		return fmt.Errorf("failed to marshal current value for revision: %v", err)
	}
	
	rev1Key := GetRevisionKey(key, 1)
	err = r.storage.StoreWithTTL(txn, []byte(rev1Key), currentValueBytes, ttl)
	if err != nil {
		return fmt.Errorf("failed to store revision 1: %v", err)
	}
	
	// Update metadata with new revision count
	metadata.UpdatedAt = time.Now().Unix()
	metadataBytes, err := json.Marshal(metadata)
	if err != nil {
		return fmt.Errorf("failed to marshal metadata: %v", err)
	}
	
	return r.storage.StoreWithTTL(txn, []byte(metadataKey), metadataBytes, ttl)
}

// GetRevisionHistory retrieves all available revisions for a given key
func (r *RevisionService) GetRevisionHistory(key string) ([]map[string]interface{}, error) {
	var revisions []map[string]interface{}
	
	err := r.storage.db.View(func(txn *badger.Txn) error {
		// Check revisions 1, 2, 3
		for rev := 1; rev <= 3; rev++ {
			revKey := GetRevisionKey(key, rev)
			
			revData, err := r.storage.RetrieveWithDecompression(txn, []byte(revKey))
			if err == badger.ErrKeyNotFound {
				continue // Skip missing revisions
			} else if err != nil {
				return fmt.Errorf("failed to retrieve revision %d: %v", rev, err)
			}
			
			var storedValue types.StoredValue
			err = json.Unmarshal(revData, &storedValue)
			if err != nil {
				return fmt.Errorf("failed to unmarshal revision %d: %v", rev, err)
			}
			
			var data interface{}
			err = json.Unmarshal(storedValue.Data, &data)
			if err != nil {
				return fmt.Errorf("failed to unmarshal revision %d data: %v", rev, err)
			}
			
			revision := map[string]interface{}{
				"revision":  rev,
				"uuid":      storedValue.UUID,
				"timestamp": storedValue.Timestamp,
				"data":      data,
			}
			
			revisions = append(revisions, revision)
		}
		
		return nil
	})
	
	if err != nil {
		return nil, err
	}
	
	// Sort revisions by revision number (newest first)
	// Note: they're already in order since we iterate 1->3, but reverse for newest first
	for i, j := 0, len(revisions)-1; i < j; i, j = i+1, j-1 {
		revisions[i], revisions[j] = revisions[j], revisions[i]
	}
	
	return revisions, nil
}

// GetSpecificRevision retrieves a specific revision of a key
func (r *RevisionService) GetSpecificRevision(key string, revision int) (*types.StoredValue, error) {
	if revision < 1 || revision > 3 {
		return nil, fmt.Errorf("invalid revision number: %d (must be 1-3)", revision)
	}
	
	var storedValue types.StoredValue
	err := r.storage.db.View(func(txn *badger.Txn) error {
		revKey := GetRevisionKey(key, revision)
		
		revData, err := r.storage.RetrieveWithDecompression(txn, []byte(revKey))
		if err != nil {
			return err
		}
		
		return json.Unmarshal(revData, &storedValue)
	})
	
	if err != nil {
		return nil, err
	}
	
	return &storedValue, nil
}

// GetRevisionFromPath extracts revision number from a path like "key/data/rev/2"
func GetRevisionFromPath(path string) (string, int, error) {
	parts := strings.Split(path, "/")
	if len(parts) < 4 || parts[len(parts)-2] != "rev" {
		return "", 0, fmt.Errorf("invalid revision path format")
	}
	
	revisionStr := parts[len(parts)-1]
	revision, err := strconv.Atoi(revisionStr)
	if err != nil {
		return "", 0, fmt.Errorf("invalid revision number: %s", revisionStr)
	}
	
	// Reconstruct the base key without the "/rev/N" suffix
	baseKey := strings.Join(parts[:len(parts)-2], "/")
	
	return baseKey, revision, nil
}