/**
 * File type validation utilities for preventing malicious uploads
 * Specifically designed to prevent SVG XSS attacks and other security issues
 */

export const ALLOWED_IMAGE_TYPES = [
  'image/jpeg',
  'image/jpg',
  'image/png',
  'image/gif',
  'image/webp'
] as const;

export const ALLOWED_EXTENSIONS = ['.jpg', '.jpeg', '.png', '.gif', '.webp'] as const;

/**
 * Validate file type by MIME type
 * @param file - File object to validate
 * @returns boolean indicating if file type is allowed
 */
export function validateImageType(file: File): boolean {
  return ALLOWED_IMAGE_TYPES.includes(file.type as any);
}

/**
 * Validate file extension
 * @param filename - Filename to validate
 * @returns boolean indicating if extension is allowed
 */
export function validateImageExtension(filename: string): boolean {
  const extension = filename.toLowerCase().substring(filename.lastIndexOf('.'));
  return ALLOWED_EXTENSIONS.includes(extension as any);
}

/**
 * Comprehensive file validation
 * @param file - File object to validate
 * @returns object with validation result and error message
 */
export function validateImageUpload(file: File): { isValid: boolean; error?: string } {
  // Check file type
  if (!validateImageType(file)) {
    return {
      isValid: false,
      error: 'Invalid file type. Only JPEG, PNG, GIF, and WebP files are allowed.'
    };
  }

  // Check file extension (double check for security)
  if (!validateImageExtension(file.name)) {
    return {
      isValid: false,
      error: 'Invalid file extension. Only .jpg, .jpeg, .png, .gif, and .webp files are allowed.'
    };
  }

  // Additional security checks
  if (file.name.toLowerCase().includes('.svg')) {
    return {
      isValid: false,
      error: 'SVG files are not allowed for security reasons.'
    };
  }

  return { isValid: true };
}