import showdown from "showdown";
import yaml from "yaml";
import { promises as fs } from "fs";

function splitPostHeader(postData: string): [string, string] {
  if (postData.startsWith("---\n")) {
    const headerEndIndex = postData.indexOf("\n---\n", 4);

    return [
      postData.substring(4, headerEndIndex),
      postData.substring(headerEndIndex + 5),
    ];
  }
  return ["", postData];
}

declare interface PostMetadata {
  name: string;
  unlisted?: boolean;
  tags?: Array<string>;
  description?: string;
}

declare interface PostEntry {
  name: string;
  id: string;
  description: string | null;
}

const baseTemplate = await fs.readFile("template.html", { encoding: "utf-8" });
class PostCollector {
  allPosts: PostEntry[] = [];
  makeHtmlForPost(postMetadata: PostMetadata, markdown: string): string {
    const converter = new showdown.Converter();
    const htmlPostBody = converter.makeHtml(markdown);
    const variables = {
      postBody: htmlPostBody,
      title: postMetadata.name,
    };
    return baseTemplate.replace(
      /%([a-zA-Z]+)%/g,
      (_, match) => variables[match] ?? `Missing variable: ${match}`,
    );
  }

  async run() {
    await fs.rm("build", { recursive: true });
    await fs.mkdir("build");
    await fs.mkdir("build/posts");

    const posts = await fs.readdir("posts");
    for (let postPath of posts) {
      const totalPostPath = `posts/${postPath}`;
      if (!postPath.endsWith(".md")) {
        await fs.copyFile(totalPostPath, `build/posts/${postPath}`);
        continue;
      }
      const postId = postPath.replace(".md", "");
      const postText = await fs.readFile(totalPostPath, { encoding: "utf-8" });
      const [postHeader, postBody] = splitPostHeader(postText);
      const postMetadata = yaml.parse(postHeader) as PostMetadata;
      const postHtml = this.makeHtmlForPost(postMetadata, postBody);
      const targetPath = `build/posts/${postId}.html`;
      await fs.writeFile(targetPath, postHtml, { encoding: "utf-8" });
      if (!postMetadata.unlisted)
        this.allPosts.push({
          name: postMetadata.name,
          id: postId,
          description: postMetadata.description ?? null,
        });
    }
    await fs.writeFile(
      "build/posts/index.html",
      this.makeHtmlForPost(
        { name: "Post Index" },
        "# Post List\n" +
          this.allPosts
            .map(
              (post) =>
                `## [${post.name}](./${post.id}.html)\n\n${post.description ?? ""}`,
            )
            .join("\n"),
      ),
      { encoding: "utf-8" },
    );
  }
}

await new PostCollector().run();