feat: sitemap generation

Automatically generates the sitemap upon deploy and pings the search
engines. A bit naive but it works. Uses Ruby because this is a book
about using Ruby.

.github/workflows/gh-pages.yml

@@ -22,6 +22,16 @@ jobs:
 
       - run: mdbook build
 
+      - uses: actions/checkout@v3
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@359bebbc29cbe6c87da6bc9ea3bc930432750108
+        with:
+          ruby-version: '3.1'
+      - name: Install dependencies
+        run: bundle install
+
+      - run: ./bin/sitemap.rb
+
       - name: Deploy
         uses: peaceiris/actions-gh-pages@v3
         if: ${{ github.ref == 'refs/heads/main' }}

Gemfile

@@ -0,0 +1,3 @@
+source "https://rubygems.org"
+
+gem 'sitemap_generator', '~> 6.3'

Gemfile.lock

@@ -0,0 +1,15 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    builder (3.2.4)
+    sitemap_generator (6.3.0)
+      builder (~> 3.0)
+
+PLATFORMS
+  arm64-darwin-21
+
+DEPENDENCIES
+  sitemap_generator (~> 6.3)
+
+BUNDLED WITH
+   2.3.23

bin/sitemap.rb

@@ -0,0 +1,20 @@
+#!/usr/bin/env ruby
+require 'rubygems'
+require 'sitemap_generator'
+
+puts `mdbook build`
+
+SitemapGenerator::Sitemap.default_host = 'https://book.dragonriders.community'
+SitemapGenerator::Sitemap.public_path = 'book'
+SitemapGenerator::Sitemap.compress = false
+SitemapGenerator::Sitemap.create do
+  add '/', changefreq: 'weekly', priority: 0.9
+
+  # assumes no nested URLs
+  Dir.glob('book/*.html').each do |file|
+    file = file.split('/').last
+    next if file == "index.html"
+    add "/#{file}", changefreq: 'weekly'
+  end
+end
+SitemapGenerator::Sitemap.ping_search_engines