package storage

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"time"
)

// Storage handles local file system operations for FIT files
type Storage struct {
	outputDir string
}

// New creates a new Storage instance
func New(outputDir string) (*Storage, error) {
	// Create output directory if it doesn't exist
	if err := os.MkdirAll(outputDir, 0755); err != nil {
		return nil, fmt.Errorf("failed to create output directory: %w", err)
	}

	return &Storage{
		outputDir: outputDir,
	}, nil
}

// Save saves a FIT file to the output directory
func (s *Storage) Save(activityID int64, activityName string, date time.Time, data []byte) (string, error) {
	// Generate filename
	filename := s.generateFilename(activityID, activityName, date)
	filepath := filepath.Join(s.outputDir, filename)

	// Check if file already exists
	if _, err := os.Stat(filepath); err == nil {
		return filepath, nil // File already exists, no need to save
	}

	// Write to temporary file first (atomic write)
	tmpFile := filepath + ".tmp"
	if err := os.WriteFile(tmpFile, data, 0644); err != nil {
		return "", fmt.Errorf("failed to write temporary FIT file: %w", err)
	}

	// Verify file integrity (non-zero size)
	if len(data) == 0 {
		_ = os.Remove(tmpFile)
		return "", fmt.Errorf("FIT file is empty")
	}

	// Rename temporary file to actual file (atomic operation)
	if err := os.Rename(tmpFile, filepath); err != nil {
		_ = os.Remove(tmpFile)
		return "", fmt.Errorf("failed to rename temporary FIT file: %w", err)
	}

	return filepath, nil
}

// Exists checks if a FIT file already exists for an activity
func (s *Storage) Exists(activityID int64) bool {
	// List files in output directory
	files, err := os.ReadDir(s.outputDir)
	if err != nil {
		return false
	}

	// Check if any file starts with the activity ID
	prefix := fmt.Sprintf("%d_", activityID)
	for _, file := range files {
		if strings.HasPrefix(file.Name(), prefix) {
			return true
		}
	}

	return false
}

// generateFilename generates a filename for a FIT file
// Format: {activityID}_{date}_{name}.fit
func (s *Storage) generateFilename(activityID int64, activityName string, date time.Time) string {
	// Format date as YYYY-MM-DD
	dateStr := date.Format("2006-01-02")

	// Sanitize activity name (remove special characters)
	name := sanitizeFilename(activityName)
	if name == "" {
		name = "activity"
	}

	// Limit name length
	if len(name) > 50 {
		name = name[:50]
	}

	return fmt.Sprintf("%d_%s_%s.fit", activityID, dateStr, name)
}

// sanitizeFilename removes special characters from filename
func sanitizeFilename(name string) string {
	// Replace spaces with dashes
	name = strings.ReplaceAll(name, " ", "-")

	// Remove special characters (keep alphanumeric, dash, underscore)
	re := regexp.MustCompile(`[^a-zA-Z0-9_-]`)
	name = re.ReplaceAllString(name, "")

	// Remove multiple consecutive dashes
	re = regexp.MustCompile(`-+`)
	name = re.ReplaceAllString(name, "-")

	// Trim dashes from start and end
	name = strings.Trim(name, "-")

	return name
}