package store

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/klauspost/compress/zstd"
)

// Store handles encrypted file storage
type Store struct {
	basePath string
	key      []byte
	gcm      cipher.AEAD
	encoder  *zstd.Encoder
	decoder  *zstd.Decoder
}

// New creates a new encrypted file store
func New(basePath string, key []byte) (*Store, error) {
	// Ensure base path exists
	if err := os.MkdirAll(basePath, 0755); err != nil {
		return nil, fmt.Errorf("failed to create base path: %w", err)
	}

	// Create AES cipher
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, fmt.Errorf("failed to create AES cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("failed to create GCM: %w", err)
	}

	// Create compression encoder/decoder
	encoder, err := zstd.NewWriter(nil, zstd.WithEncoderLevel(zstd.SpeedFastest))
	if err != nil {
		return nil, fmt.Errorf("failed to create zstd encoder: %w", err)
	}

	decoder, err := zstd.NewReader(nil)
	if err != nil {
		return nil, fmt.Errorf("failed to create zstd decoder: %w", err)
	}

	return &Store{
		basePath: basePath,
		key:      key,
		gcm:      gcm,
		encoder:  encoder,
		decoder:  decoder,
	}, nil
}

// Store saves data to encrypted storage and returns the file path
func (s *Store) Store(entryID string, data []byte) (string, string, error) {
	// Calculate hash of original data
	hash := fmt.Sprintf("%x", sha256.Sum256(data))

	// Compress data
	compressed := s.encoder.EncodeAll(data, nil)

	// Encrypt compressed data
	nonce := make([]byte, s.gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", "", fmt.Errorf("failed to generate nonce: %w", err)
	}

	encrypted := s.gcm.Seal(nonce, nonce, compressed, nil)

	// Generate date-based path
	now := time.Now()
	datePath := fmt.Sprintf("%d/%02d", now.Year(), now.Month())
	fullDir := filepath.Join(s.basePath, datePath)

	// Ensure directory exists
	if err := os.MkdirAll(fullDir, 0755); err != nil {
		return "", "", fmt.Errorf("failed to create date directory: %w", err)
	}

	// Write encrypted data
	filePath := filepath.Join(datePath, entryID+".enc")
	fullPath := filepath.Join(s.basePath, filePath)

	if err := os.WriteFile(fullPath, encrypted, 0644); err != nil {
		return "", "", fmt.Errorf("failed to write encrypted file: %w", err)
	}

	return filePath, hash, nil
}

// Retrieve loads and decrypts data from storage
func (s *Store) Retrieve(filePath string) ([]byte, error) {
	fullPath := filepath.Join(s.basePath, filePath)

	// Read encrypted data
	encrypted, err := os.ReadFile(fullPath)
	if err != nil {
		return nil, fmt.Errorf("failed to read encrypted file: %w", err)
	}

	// Extract nonce
	if len(encrypted) < s.gcm.NonceSize() {
		return nil, fmt.Errorf("encrypted data too short")
	}

	nonce := encrypted[:s.gcm.NonceSize()]
	ciphertext := encrypted[s.gcm.NonceSize():]

	// Decrypt
	compressed, err := s.gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to decrypt data: %w", err)
	}

	// Decompress
	data, err := s.decoder.DecodeAll(compressed, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to decompress data: %w", err)
	}

	return data, nil
}

// Delete removes a file from storage
func (s *Store) Delete(filePath string) error {
	fullPath := filepath.Join(s.basePath, filePath)
	return os.Remove(fullPath)
}

// Exists checks if a file exists in storage
func (s *Store) Exists(filePath string) bool {
	fullPath := filepath.Join(s.basePath, filePath)
	_, err := os.Stat(fullPath)
	return err == nil
}

// StoreTemp saves data to temporary storage for processing
func (s *Store) StoreTemp(filename string, data []byte) (string, error) {
	tempDir := filepath.Join(s.basePath, "temp")
	if err := os.MkdirAll(tempDir, 0755); err != nil {
		return "", fmt.Errorf("failed to create temp directory: %w", err)
	}

	// Sanitize filename
	sanitized := sanitizeFilename(filename)
	tempPath := filepath.Join(tempDir, fmt.Sprintf("%d_%s", time.Now().Unix(), sanitized))

	if err := os.WriteFile(tempPath, data, 0644); err != nil {
		return "", fmt.Errorf("failed to write temp file: %w", err)
	}

	return tempPath, nil
}

// CleanupTemp removes temporary files older than the specified duration
func (s *Store) CleanupTemp(maxAge time.Duration) error {
	tempDir := filepath.Join(s.basePath, "temp")
	
	entries, err := os.ReadDir(tempDir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil // No temp directory, nothing to clean
		}
		return fmt.Errorf("failed to read temp directory: %w", err)
	}

	cutoff := time.Now().Add(-maxAge)

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}

		info, err := entry.Info()
		if err != nil {
			continue
		}

		if info.ModTime().Before(cutoff) {
			filePath := filepath.Join(tempDir, entry.Name())
			os.Remove(filePath) // Ignore errors, best effort cleanup
		}
	}

	return nil
}

// GetStats returns storage statistics
func (s *Store) GetStats() (*StorageStats, error) {
	stats := &StorageStats{}

	err := filepath.Walk(s.basePath, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		if !info.IsDir() {
			stats.TotalFiles++
			stats.TotalSize += info.Size()

			if strings.HasSuffix(info.Name(), ".enc") {
				stats.EncryptedFiles++
				stats.EncryptedSize += info.Size()
			}
		}

		return nil
	})

	return stats, err
}

// StorageStats represents storage usage statistics
type StorageStats struct {
	TotalFiles     int   `json:"total_files"`
	TotalSize      int64 `json:"total_size"`
	EncryptedFiles int   `json:"encrypted_files"`
	EncryptedSize  int64 `json:"encrypted_size"`
}

// Close cleanly shuts down the store
func (s *Store) Close() error {
	s.encoder.Close()
	s.decoder.Close()
	return nil
}

// Helper functions

func sanitizeFilename(filename string) string {
	// Replace unsafe characters
	unsafe := []string{"/", "\\", ":", "*", "?", "\"", "<", ">", "|"}
	safe := filename
	
	for _, char := range unsafe {
		safe = strings.ReplaceAll(safe, char, "_")
	}

	// Limit length
	if len(safe) > 200 {
		safe = safe[:200]
	}

	return safe
}