build.yml

# This script creates a nice README.md with an index of all TIL files.
# TIL files are Markdown files named anything other than README.md.
#
# The readme is split into two sections: the "header" and the "index",
# separated by three hyphens on their own line.
# Anything above the three hyphens is the "header" and will be kept as is.
# Anything below will be replaced by the "index".

name: Build README

on:
  push:
    branches:
      - main

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Check out repo
        uses: actions/checkout@v3
        with:
          fetch-depth: 0 # get full history or else it'll be overwritten

      - name: Regenerate README
        uses: actions/github-script@v6
        with:
          script: |
            const { readFile, writeFile } = require("node:fs/promises");

            console.log("Building index…");

            // load readme
            let readme = await readFile("README.md").then(file => file.toString());

            // add header separator
            const separator = "\n---\n";
            const index = readme.indexOf(separator);
            if (index === -1) readme += separator;
            else readme = readme.substring(0, index + separator.length);

            // collect entries
            const files = await glob.create("./**/*.md").then(globber => globber.glob());
            const entries = files
              .filter(name => !name.endsWith("/README.md")) // exclude README.md
              .sort()
              .map(name => name.split("/").slice(-2));

            // add summary
            readme += `\n${entries.length} TILs so far:\n`;

            // create category map
            const categories = new Map();
            for (const [category, file] of entries) {
              const list = categories.get(category) || [];
              categories.set(category, [...list, file]);
            }

            // create a section for each category
            for (const [category, entries] of categories.entries()) {
              // write category header
              readme += `\n## ${category}\n\n`;

              // write link for each file
              for (const file of entries) {
                const filepath = [category, file].join("/");
                const contents = await readFile(filepath).then(file => file.toString());
                const [, title] = contents.match(/^# (.+)$/m);
                readme += `- [${title}](/${filepath})\n`;
              }
            }

            // write readme
            await writeFile("README.md", readme);

      - name: Install NPM libraries
        run: npm install marked he

      - name: Generate RSS
        uses: actions/github-script@v6
        with:
          script: |
            const { readFile, writeFile, stat } = require("node:fs/promises");
            const { promisify } = require("node:util");
            const run = promisify(require("node:child_process").exec);

            const marked = require("marked").marked;
            const he = require("he");

            console.log("Building feed…");

            // collect entries
            const files = await glob.create("./**/*.md").then(globber => globber.glob());
            const modified = files
              .filter(name => !name.includes("/node_modules/")) // exclude node_modules
              .filter(name => !name.endsWith("/README.md")) // exclude README.md
              .map(name => name.split("/").slice(-2).join("/"))
              .map(async file => [file, await run("git log --follow --format=%ad --date=unix " + file)]);

            const entries = await Promise.all(modified);
            const sorted = entries
              .map(([name, created]) => [name, created.stdout.trim().split("\n").at(-1)])
              .sort(([, a], [, b]) => b.localeCompare(a))
              .slice(0, 10)
              .map(async ([name, date]) => ({
                name,
                date: new Date(Number(date) * 1000),
                content: await readFile(name).then(buf => buf.toString())
              }));
            const feed = await Promise.all(sorted);

            const user = context.repo.owner;
            const repo = context.repo.repo;
            const branch = context.payload.repository.default_branch;

            const link = `https://github.com/${user}/${repo}`;

            const rss = [];
            rss.push(`<?xml version="1.0" encoding="UTF-8"?>`);
            rss.push(`<rss version="2.0" xmlns:content="http://purl.org/rss/1.0/modules/content/">`);
            rss.push(`<channel>`);
            rss.push(`<title>${user} TIL</title>`);
            rss.push(`<description>A collection of useful things I've learned.</description>`);
            rss.push(`<link>${link}</link>`);

            const dateOptions = { year: "numeric", month: "short", day: "numeric", hour: "2-digit", minute: "2-digit", second: "2-digit", timeZoneName: "short" };
            for (const item of feed) {
              rss.push(`<item>`);

              const itemLink = `${link}/blob/${branch}/${item.name}`;
              rss.push(`<guid>${itemLink}</guid>`);
              rss.push(`<link>${itemLink}</link>`);

              const category = item.name.split("/")[0];
              const [, title] = item.content.match(/^# (.+)$/m);
              rss.push(`<title>TIL (${category}): ${he.escape(title)}</title>`);

              const pubDate = new Intl.DateTimeFormat("en-US", dateOptions).format(item.date);
              rss.push(`<pubDate>${item.date.toUTCString()}</pubDate>`);

              const content = item.content.split("\n").slice(1).join("\n").trim();
              const encoded = he.escape(marked(content));
              rss.push(`<content:encoded>${encoded}</content:encoded>`);

              rss.push(`</item>`);
            }

            rss.push(`</channel>`);
            rss.push(`</rss>`);


            // write feed
            await writeFile("rss.xml", rss.join("\n"));

      - name: Commit and push if README or RSS changed
        run: |-
          git config --global user.email "actions@users.noreply.github.com"
          git config --global user.name "tilbot"
          git diff --quiet || git commit --all --message "Update README.md or rss.xml"
          git push