Parser from markdown to wordpress for RayWenderlich website

ray-parser.rb

#!/usr/bin/ruby
require 'redcarpet'

class RayParser < Redcarpet::Render::HTML

  # *important concept*
  def emphasis(text)
    "<i>#{text}</i>"
  end

  # filenames, menus. e.g.: **App.java**
  def double_emphasis(text)
    "<em>#{text}</em>"
  end

  def header(text, level)
    case level
    when 1
      "<h2>#{text}</h2>\n"
    when 2
      "<h3>#{text}</h3>\n"
    when 3
      "<em>#{text}</em>\n"
    else
      throw "Unsupported header level #{level}"
    end
  end

  def block_code(code, language)
    "<pre lang=\"#{language}\">\n#{code}</pre>"
  end

  # Wordpress will insert <p> tags
  def paragraph(text)
    "\n#{text}\n"
  end

  # Wordpress will escape ampersands and single quotes
  def postprocess(doc)
    doc.gsub("&amp;", ?&)
      .gsub("&#39;", ?')
  end

end

if ARGV.size != 1
  puts "Usage: #{$PROGRAM_NAME} file.md"
  exit
end

markdown = Redcarpet::Markdown.new(RayParser, extensions = { fenced_code_blocks: true, disable_indented_code_blocks: true } )
text = File.read(ARGV[0])
puts markdown.render(text)

Example text:

# Header 1

## Header 2

### Header 3

A paragraph

1. one
2. two
3. three

- one
- two
- three

*Important* concept
**File.java**

Output:

 % ./parser.rb test.md
<h2>Header 1</h2>
<h3>Header 2</h3>
<em>Header 3</em>

A paragraph

<ol>
<li>one</li>
<li>two</li>
<li>three</li>
</ol>

<ul>
<li>one</li>
<li>two</li>
<li>three</li>
</ul>

<i>Important</i> concept
<em>File.java</em>

Code blocks:

```java
code
```

Output:

<pre lang="java">
code
</pre>