gistfile1.rb

module RenderToHTML
  def self.book
    [title, css, body].join("\n")
  end

  private

  def self.title
    commit_hash = `git log -1 --pretty="format:%H"`
    %{
      <div class="title">
        <h1>#{TITLE}</h1>
        <p>by Gary Bernhardt</p>
        <p>partial build on commit #{commit_hash}</p>
      </div>
      <div class="do_not_distribute">
        <h1>DO NOT DISTRIBUTE</h1>
      </div>
    }
  end

  def self.css
    %{
    <style>
      body {
        font-family: Helvetica;
        width: 550px;
        margin: auto;
      }

      .do_not_distribute { margin: 16em 0; }
      .title { margin: 4em 0 8em 0; }
      .title, h1, h2, h3 { text-align: center; }
      h2 { margin-top: 8em; }
      h3 { margin-top: 8em; }
      p, li { line-height: 1.5em; }
      figure, img { margin: 0 0 1em 0; padding: 0; }
    </style>
    }
  end

  def self.body
    # Only render to markdown once we have all of the body stuff (sections and
    # chapters).
    RenderToMarkdown.sections.map do |section|
      RenderExternalFormats.markdown(section)
    end
  end
end

class RenderToMarkdown
  def self.sections
    BOOK.sections.map { |section| section(section) }.flatten
  end

  private

  def self.section(section)
    [
      "## Part #{section.number}. #{section.name}"
    ] + chapters(section.chapters)
  end

  def self.chapters(chapters)
    chapters.map do |chapter|
      [
        "### #{chapter.number}. #{chapter.title}",
        chapter(chapter)
      ]
    end
  end

  def self.chapter(chapter)
    RenderExternalFormats.erb(chapter.content)
  end
end

class RenderExternalFormats
  def self.erb(markdown)
    context = Context.new
    rendered = ERB.new(markdown).result(context.binding)
  end

  def self.markdown(markdown)
    Open3.popen2("multimarkdown") do |stdin, stdout|
      stdin.write(markdown)
      stdin.close
      stdout.read
    end
  end
end

gistfile2.rb

# Here's the whole RenderToMarkdown class inlined into the RenderToHTML.book method:

  def self.book
    [
      title,
      css,
      BOOK.sections.map do |section|
        [
          "## Part #{section.number}. #{section.name}",
          section.chapters.map do |chapter|
            [
              "### #{chapter.number}. #{chapter.title}",
              RenderExternalFormats.erb(chapter.content),
            ]
          end,
        ]
      end.flatten.map do |markdown|
        RenderExternalFormats.markdown(markdown)
      end
    ].flatten.join("\n")
  end