type MarkdownExportFileNameInput = {
  slug: string;
  id: number;
};

function isAbsoluteOrSpecialUrl(url: string): boolean {
  return /^(https?:)?\/\//i.test(url) || /^data:/i.test(url);
}

export function normalizeMarkdownImageUrls(markdown: string, origin: string): string {
  const normalizedOrigin = origin.replace(/\/+$/, "");

  return markdown.replace(/!\[([^\]]*)\]\(([^)\s]+)([^)]*)\)/g, (full, alt, rawUrl, rest) => {
    if (isAbsoluteOrSpecialUrl(rawUrl)) {
      return full;
    }

    if (!rawUrl.startsWith("/")) {
      return full;
    }

    return `![${alt}](${normalizedOrigin}${rawUrl}${rest})`;
  });
}

export function buildMarkdownExportFileName(input: MarkdownExportFileNameInput): string {
  const base = input.slug.trim() || `post-${input.id}`;
  return `${base}.md`;
}

export function downloadMarkdownFile(filename: string, content: string): void {
  if (typeof window === "undefined" || typeof document === "undefined") {
    return;
  }

  const blob = new Blob([content], { type: "text/markdown;charset=utf-8" });
  const url = URL.createObjectURL(blob);
  const anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = filename;
  anchor.style.display = "none";
  document.body.appendChild(anchor);
  anchor.click();
  anchor.remove();
  URL.revokeObjectURL(url);
}