/** Allowed MIME types for receipt/item image uploads (server-side check). */
const ALLOWED_IMAGE_TYPES = new Set([
  "image/jpeg",
  "image/png",
  "image/webp",
  "image/heic",
  "image/heif",
]);

/** Max size 10MB. */
const MAX_IMAGE_BYTES = 10 * 1024 * 1024;

/**
 * Validates an image file for upload. Returns an error message if invalid, or null if valid/no file.
 * Use in form actions before sending the file to PocketBase.
 */
export function validateImageUpload(file: File | null): string | null {
  if (!file || file.size === 0) return null;
  const type = (file.type ?? "").toLowerCase();
  const name = file.name.toLowerCase();
  const isHeic =
    type === "image/heic" ||
    type === "image/heif" ||
    name.endsWith(".heic") ||
    name.endsWith(".heif");
  if (!isHeic && !ALLOWED_IMAGE_TYPES.has(type)) {
    return "Invalid image type. Use JPEG, PNG, WebP, or HEIC.";
  }
  if (file.size > MAX_IMAGE_BYTES) {
    return `Image must be under ${MAX_IMAGE_BYTES / 1024 / 1024}MB.`;
  }
  return null;
}