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

import glob from "fast-glob";
import { decode } from "html-entities";
import { unified } from "unified";

import { rehypeSanitize, rehypeStringify } from "@/lib/rehype";
import {
  remarkFrontmatter,
  remarkMdx,
  remarkParse,
  remarkRehype,
  remarkSmartypants,
  remarkStripMdxImportsExports,
} from "@/lib/remark";

export type FrontMatter = {
  slug: string;
  permalink: string;
  date: string;
  title: string;
  htmlTitle?: string;
  description?: string;
  tags?: string[];
  image?: string;
  noComments?: boolean;
};

/** Path to directory with .mdx files, relative to project root. */
export const POSTS_DIR = "notes" as const;

/** Use filesystem to get a simple list of all post slugs */
export const getSlugs = async (): Promise<string[]> => {
  "use cache";

  // list all .mdx files in POSTS_DIR
  const mdxFiles = await glob("*/index.mdx", {
    cwd: path.join(process.cwd(), POSTS_DIR),
    dot: false,
  });

  // strip the .mdx extensions from filenames
  const slugs = mdxFiles.map((fileName) => fileName.replace(/\/index\.mdx$/, ""));

  return slugs;
};

export const getFrontMatter: {
  /**
   * Parses and returns the front matter of ALL posts, sorted reverse chronologically
   */
  (): Promise<FrontMatter[]>;
  /**
   * Parses and returns the front matter of a given slug, or undefined if the slug does not exist
   */
  (slug: string): Promise<FrontMatter | undefined>;
} = (async (slug?: string) => {
  "use cache";

  if (typeof slug === "string") {
    try {
      const { frontmatter } = await import(`../${POSTS_DIR}/${slug}/index.mdx`);

      // process markdown title to html...
      const htmlTitle = await unified()
        .use(remarkParse)
        .use(remarkSmartypants)
        .use(remarkRehype)
        .use(rehypeSanitize, {
          // allow *very* limited markdown to be used in post titles
          tagNames: ["code", "em", "strong"],
        })
        .use(rehypeStringify)
        .process(frontmatter.title)
        .then((result) => result.toString().trim());

      // ...and then (sketchily) remove said html for a plaintext version:
      // https://css-tricks.com/snippets/javascript/strip-html-tags-in-javascript/
      const title = decode(htmlTitle.replace(/<[^>]*>/g, ""));

      return {
        ...(frontmatter as Partial<FrontMatter>),
        // plain title without html or markdown syntax:
        title,
        // stylized title with limited html tags:
        htmlTitle,
        slug,
        // validate/normalize the date string provided from front matter
        date: new Date(frontmatter.date).toISOString(),
        permalink: `${process.env.NEXT_PUBLIC_BASE_URL}/${POSTS_DIR}/${slug}`,
      } as FrontMatter;
    } catch (error) {
      console.error(`Failed to load front matter for post with slug "${slug}":`, error);
      return undefined;
    }
  }

  if (!slug) {
    // concurrently fetch the front matter of each post
    const slugs = await getSlugs();
    const allPosts = await Promise.all(slugs.map(getFrontMatter));

    // filter out any undefined entries from failed imports
    const posts = allPosts.filter((p): p is FrontMatter => !!p);

    // sort the results reverse chronologically and return
    return posts.sort(
      (post1, post2) => new Date(post2.date).getTime() - new Date(post1.date).getTime(),
    );
  }

  throw new Error("getFrontMatter() called with invalid argument.");
}) as typeof getFrontMatter;

/** Returns the content of a post with very limited processing to include in RSS feeds */
export const getContent = async (slug: string): Promise<string | undefined> => {
  "use cache";

  try {
    const content = await unified()
      .use(remarkParse)
      .use(remarkMdx)
      .use(remarkStripMdxImportsExports)
      .use(remarkFrontmatter)
      .use(remarkSmartypants)
      .use(remarkRehype)
      .use(rehypeSanitize, {
        tagNames: [
          "p",
          "a",
          "em",
          "strong",
          "code",
          "pre",
          "blockquote",
          "del",
          "h1",
          "h2",
          "h3",
          "h4",
          "h5",
          "h6",
          "ul",
          "ol",
          "li",
          "hr",
        ],
      })
      .use(rehypeStringify)
      .process(await fs.readFile(path.join(process.cwd(), `${POSTS_DIR}/${slug}/index.mdx`)));

    // convert the parsed content to a string with "safe" HTML
    return content
      .toString()
      .replaceAll("/* prettier-ignore */", "")
      .replaceAll("<p></p>", "")
      .trim();
  } catch (error) {
    console.error(`Failed to load/parse content for post with slug "${slug}":`, error);
    return undefined;
  }
};