Static blog with front page summary

Goal: have a personal blog, and try out another point in the 'modular
app design with elixir' space.

Designing OTP systems with elixir had some interesting ideas.

blogex/lib/blogex/feed.ex

@@ -0,0 +1,139 @@
+defmodule Blogex.Feed do
+  @moduledoc """
+  Generates RSS 2.0 and Atom feeds for a blog.
+
+  ## Usage
+
+      # In a controller or plug:
+      xml = Blogex.Feed.rss(MyApp.EngineeringBlog, "https://myapp.com")
+      conn |> put_resp_content_type("application/rss+xml") |> send_resp(200, xml)
+  """
+
+  @doc """
+  Generates an RSS 2.0 XML feed for the given blog module.
+
+  ## Options
+
+    * `:limit` - max number of posts to include (default: 20)
+    * `:language` - feed language (default: "en-us")
+  """
+  def rss(blog_module, base_url, opts \\ []) do
+    limit = Keyword.get(opts, :limit, 20)
+    language = Keyword.get(opts, :language, "en-us")
+    posts = Enum.take(blog_module.all_posts(), limit)
+
+    blog_url = "#{base_url}#{blog_module.base_path()}"
+    feed_url = "#{blog_url}/feed.xml"
+
+    pub_date =
+      case posts do
+        [latest | _] -> format_rfc822(latest.date)
+        [] -> format_rfc822(Date.utc_today())
+      end
+
+    """
+    <?xml version="1.0" encoding="UTF-8"?>
+    <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:content="http://purl.org/rss/1.0/modules/content/">
+      <channel>
+        <title>#{escape(blog_module.title())}</title>
+        <link>#{blog_url}</link>
+        <description>#{escape(blog_module.description())}</description>
+        <language>#{language}</language>
+        <pubDate>#{pub_date}</pubDate>
+        <atom:link href="#{feed_url}" rel="self" type="application/rss+xml"/>
+    #{Enum.map_join(posts, "\n", &item_xml(&1, base_url, blog_module))}
+      </channel>
+    </rss>
+    """
+    |> String.trim()
+  end
+
+  @doc """
+  Generates an Atom feed for the given blog module.
+
+  ## Options
+
+    * `:limit` - max number of posts to include (default: 20)
+  """
+  def atom(blog_module, base_url, opts \\ []) do
+    limit = Keyword.get(opts, :limit, 20)
+    posts = Enum.take(blog_module.all_posts(), limit)
+
+    blog_url = "#{base_url}#{blog_module.base_path()}"
+    feed_url = "#{blog_url}/feed.xml"
+
+    updated =
+      case posts do
+        [latest | _] -> format_iso8601(latest.date)
+        [] -> format_iso8601(Date.utc_today())
+      end
+
+    """
+    <?xml version="1.0" encoding="UTF-8"?>
+    <feed xmlns="http://www.w3.org/2005/Atom">
+      <title>#{escape(blog_module.title())}</title>
+      <link href="#{blog_url}" rel="alternate"/>
+      <link href="#{feed_url}" rel="self"/>
+      <id>#{blog_url}</id>
+      <updated>#{updated}</updated>
+    #{Enum.map_join(posts, "\n", &entry_xml(&1, base_url, blog_module))}
+    </feed>
+    """
+    |> String.trim()
+  end
+
+  # Private helpers
+
+  defp item_xml(post, base_url, blog_module) do
+    url = "#{base_url}#{blog_module.base_path()}/#{post.id}"
+
+    """
+        <item>
+          <title>#{escape(post.title)}</title>
+          <link>#{url}</link>
+          <guid isPermaLink="true">#{url}</guid>
+          <pubDate>#{format_rfc822(post.date)}</pubDate>
+          <description>#{escape(post.description)}</description>
+          <content:encoded><![CDATA[#{post.body}]]></content:encoded>
+    #{Enum.map_join(post.tags, "\n", &"      <category>#{escape(&1)}</category>")}
+        </item>
+    """
+  end
+
+  defp entry_xml(post, base_url, blog_module) do
+    url = "#{base_url}#{blog_module.base_path()}/#{post.id}"
+
+    """
+        <entry>
+          <title>#{escape(post.title)}</title>
+          <link href="#{url}" rel="alternate"/>
+          <id>#{url}</id>
+          <published>#{format_iso8601(post.date)}</published>
+          <updated>#{format_iso8601(post.date)}</updated>
+          <author><name>#{escape(post.author)}</name></author>
+          <summary>#{escape(post.description)}</summary>
+          <content type="html"><![CDATA[#{post.body}]]></content>
+    #{Enum.map_join(post.tags, "\n", &"      <category term=\"#{escape(&1)}\"/>")}
+        </entry>
+    """
+  end
+
+  defp format_rfc822(date) do
+    date
+    |> DateTime.new!(~T[00:00:00], "Etc/UTC")
+    |> Calendar.strftime("%a, %d %b %Y %H:%M:%S +0000")
+  end
+
+  defp format_iso8601(date) do
+    "#{Date.to_iso8601(date)}T00:00:00Z"
+  end
+
+  defp escape(text) when is_binary(text) do
+    text
+    |> String.replace("&", "&amp;")
+    |> String.replace("<", "&lt;")
+    |> String.replace(">", "&gt;")
+    |> String.replace("\"", "&quot;")
+    |> String.replace("'", "&apos;")
+  end
+end