package storage

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/openaccounting/oa-server/core/util/id"
)

// LocalStorage implements the Storage interface for local filesystem
type LocalStorage struct {
	rootDir string
	baseURL string
}

// NewLocalStorage creates a new local filesystem storage backend
func NewLocalStorage(config LocalConfig) (*LocalStorage, error) {
	rootDir := config.RootDir
	if rootDir == "" {
		rootDir = "./uploads"
	}
	
	// Ensure the root directory exists
	if err := os.MkdirAll(rootDir, 0755); err != nil {
		return nil, fmt.Errorf("failed to create storage directory: %w", err)
	}
	
	return &LocalStorage{
		rootDir: rootDir,
		baseURL: config.BaseURL,
	}, nil
}

// Store saves a file to the local filesystem
func (l *LocalStorage) Store(filename string, content io.Reader, contentType string) (string, error) {
	// Generate a unique storage path
	storagePath := l.generateStoragePath(filename)
	fullPath := filepath.Join(l.rootDir, storagePath)
	
	// Ensure the directory exists
	dir := filepath.Dir(fullPath)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return "", fmt.Errorf("failed to create directory: %w", err)
	}
	
	// Create and write the file
	file, err := os.Create(fullPath)
	if err != nil {
		return "", fmt.Errorf("failed to create file: %w", err)
	}
	defer file.Close()
	
	_, err = io.Copy(file, content)
	if err != nil {
		// Clean up the file if write failed
		os.Remove(fullPath)
		return "", fmt.Errorf("failed to write file: %w", err)
	}
	
	return storagePath, nil
}

// Retrieve gets a file from the local filesystem
func (l *LocalStorage) Retrieve(path string) (io.ReadCloser, error) {
	// Validate path to prevent directory traversal
	if err := l.validatePath(path); err != nil {
		return nil, err
	}
	
	fullPath := filepath.Join(l.rootDir, path)
	file, err := os.Open(fullPath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, &FileNotFoundError{Path: path}
		}
		return nil, fmt.Errorf("failed to open file: %w", err)
	}
	
	return file, nil
}

// Delete removes a file from the local filesystem
func (l *LocalStorage) Delete(path string) error {
	// Validate path to prevent directory traversal
	if err := l.validatePath(path); err != nil {
		return err
	}
	
	fullPath := filepath.Join(l.rootDir, path)
	err := os.Remove(fullPath)
	if err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("failed to delete file: %w", err)
	}
	
	// Try to remove empty parent directories
	l.cleanupEmptyDirs(filepath.Dir(fullPath))
	
	return nil
}

// GetURL returns a URL for accessing the file
func (l *LocalStorage) GetURL(path string, expiry time.Duration) (string, error) {
	// Validate path to prevent directory traversal
	if err := l.validatePath(path); err != nil {
		return "", err
	}
	
	// Check if file exists
	exists, err := l.Exists(path)
	if err != nil {
		return "", err
	}
	if !exists {
		return "", &FileNotFoundError{Path: path}
	}
	
	if l.baseURL != "" {
		// Return a public URL if base URL is configured
		return l.baseURL + "/" + path, nil
	}
	
	// For local storage without a base URL, return the file path
	// In a real application, you might serve these through an endpoint
	return "/files/" + path, nil
}

// Exists checks if a file exists at the given path
func (l *LocalStorage) Exists(path string) (bool, error) {
	// Validate path to prevent directory traversal
	if err := l.validatePath(path); err != nil {
		return false, err
	}
	
	fullPath := filepath.Join(l.rootDir, path)
	_, err := os.Stat(fullPath)
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, fmt.Errorf("failed to check file existence: %w", err)
	}
	
	return true, nil
}

// GetMetadata returns file metadata
func (l *LocalStorage) GetMetadata(path string) (*FileMetadata, error) {
	// Validate path to prevent directory traversal
	if err := l.validatePath(path); err != nil {
		return nil, err
	}
	
	fullPath := filepath.Join(l.rootDir, path)
	info, err := os.Stat(fullPath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, &FileNotFoundError{Path: path}
		}
		return nil, fmt.Errorf("failed to get file metadata: %w", err)
	}
	
	return &FileMetadata{
		Size:         info.Size(),
		LastModified: info.ModTime(),
		ContentType:  "", // Local storage doesn't store content type
		ETag:         "", // Local storage doesn't have ETags
	}, nil
}

// generateStoragePath creates a unique storage path for a file
func (l *LocalStorage) generateStoragePath(filename string) string {
	// Generate a unique ID for the file
	fileID := id.String(id.New())
	
	// Extract file extension
	ext := filepath.Ext(filename)
	
	// Create a path structure: YYYY/MM/DD/uuid.ext
	now := time.Now()
	datePath := fmt.Sprintf("%04d/%02d/%02d", now.Year(), now.Month(), now.Day())
	
	return filepath.Join(datePath, fileID+ext)
}

// validatePath ensures the path doesn't contain directory traversal attempts
func (l *LocalStorage) validatePath(path string) error {
	// Clean the path and check for traversal attempts
	cleanPath := filepath.Clean(path)
	
	// Reject paths that try to go up directories
	if strings.Contains(cleanPath, "..") {
		return &InvalidPathError{Path: path}
	}
	
	// Reject absolute paths
	if filepath.IsAbs(cleanPath) {
		return &InvalidPathError{Path: path}
	}
	
	return nil
}

// cleanupEmptyDirs removes empty parent directories up to the root
func (l *LocalStorage) cleanupEmptyDirs(dir string) {
	// Don't remove the root directory
	if dir == l.rootDir {
		return
	}
	
	// Check if directory is empty
	entries, err := os.ReadDir(dir)
	if err != nil || len(entries) > 0 {
		return
	}
	
	// Remove empty directory
	if err := os.Remove(dir); err == nil {
		// Recursively clean parent directories
		l.cleanupEmptyDirs(filepath.Dir(dir))
	}
}

// FileNotFoundError is returned when a file doesn't exist
type FileNotFoundError struct {
	Path string
}

func (e *FileNotFoundError) Error() string {
	return "file not found: " + e.Path
}

// InvalidPathError is returned when a path is invalid or contains traversal attempts
type InvalidPathError struct {
	Path string
}

func (e *InvalidPathError) Error() string {
	return "invalid path: " + e.Path
}