export function sanitizeFilenameSegment(value: string | null | undefined, fallback = ''): string {
  if (typeof value !== 'string') {
    return fallback;
  }

  const normalized = value
    .trim()
    .normalize('NFKD')
    .replace(/[\u0300-\u036f]/g, '');

  const slug = normalized.replace(/[^A-Za-z0-9]+/g, '-').replace(/^-+|-+$/g, '').toLowerCase();

  return slug.length ? slug : fallback;
}

export function normalizeEventDateSegment(dateValue: string | null | undefined): string | null {
  if (!dateValue) {
    return null;
  }

  const trimmed = dateValue.trim();
  if (!trimmed) {
    return null;
  }

  const isoCandidate = trimmed.slice(0, 10);
  if (/^\d{4}-\d{2}-\d{2}$/.test(isoCandidate)) {
    return isoCandidate;
  }

  const parsed = new Date(trimmed);
  if (Number.isNaN(parsed.getTime())) {
    return null;
  }

  return parsed.toISOString().slice(0, 10);
}

export function buildDownloadFilename(
  parts: Array<string | null | undefined>,
  extension: string,
  fallback = 'download',
): string {
  const sanitizedParts = parts
    .map((part) => sanitizeFilenameSegment(part, ''))
    .filter((segment) => segment.length > 0);

  const base = sanitizedParts.length ? sanitizedParts.join('-') : fallback;
  const cleanExtension = sanitizeFilenameSegment(extension, '').replace(/[^a-z0-9]/gi, '') || 'bin';

  return `${base}.${cleanExtension.toLowerCase()}`;
}