import { join } from "$std/path/mod.ts";
import { exists } from "$std/fs/mod.ts";
import { extract } from "$std/front_matter/yaml.ts";

const POSTS_PATH = "./posts";

export interface Post {
  slug: string; // This is the file name without the extension
  title: string;
  publishedAt: Date;
  markdown: string;
}

function validateFrontMatter(attrs: unknown): attrs is {
  title: string;
  published_at: string;
  snippet: string;
} {
  if (typeof attrs !== "object" || attrs === null) {
    return false;
  }
  // This guard is here to help typescript.
  // I trust myself to write the front matter correctly :)
  return true;
}

export async function getPost(slug: string): Promise<Post | null> {
  const path = join(POSTS_PATH, `${slug}.md`);

  if (!await exists(path)) {
    return null;
  }

  const text = await Deno.readTextFile(path);
  const { attrs, body } = extract(text);

  if (!validateFrontMatter(attrs)) {
    throw new Error("Invalid front matter");
  }

  return {
    slug,
    title: attrs.title,
    publishedAt: new Date(attrs.published_at),
    markdown: body,
  };
}

export async function listPosts(): Promise<Post[]> {
  const files = Deno.readDir(POSTS_PATH);

  const slugs: string[] = [];
  for await (const file of files) {
    const slug = file.name.replace(".md", "");
    slugs.push(slug);
  }

  const posts = await Promise.all(
    slugs.map(getPost as (slug: string) => Promise<Post> // We know that the slug exists since they come from the file system
    ),
  );
  posts.sort((a, b) => b.publishedAt.getTime() - a.publishedAt.getTime());

  return posts;
}