import "server-only";

import fs from "node:fs/promises";
import path from "node:path";

export interface MarkdownCache {
  [key: string]: string;
}

let markdownCacheInstance: MarkdownCache | null = null;
let initPromise: Promise<MarkdownCache> | null = null;

// Loads .md files from `contentDirPath` (relative to process.cwd()), strips
// frontmatter, keys entries by `/blog/<basename>`. Singleton + in-flight
// memo so SSR pages compiling in parallel share one read.
export async function loadMarkdownContent({
  contentDirPath,
}: {
  contentDirPath: string;
}): Promise<MarkdownCache> {
  if (markdownCacheInstance !== null) return markdownCacheInstance;
  if (initPromise !== null) return initPromise;

  initPromise = (async () => {
    const cache: MarkdownCache = {};
    const contentDir = path.join(process.cwd(), contentDirPath);
    const files = await fs.readdir(contentDir);
    await Promise.all(
      files
        .filter((file) => file.endsWith(".md"))
        .map(async (file) => {
          const filePath = path.join(contentDir, file);
          const content = await fs.readFile(filePath, "utf-8");
          const body = content.replace(/^---\n[\s\S]*?\n---\n/, "");
          const slug = `/blog/${file.replace(".md", "")}`;
          cache[slug] = body;
        }),
    );
    markdownCacheInstance = cache;
    return cache;
  })();

  return initPromise;
}

export function getMarkdownFromCache(cache: MarkdownCache, key: string): string | undefined {
  return cache[key];
}

export function clearMarkdownCache(): void {
  markdownCacheInstance = null;
  initPromise = null;
}