class GitHub::Markup::CommandImplementation

def call_block(rendered, content)
  if block && block.arity == 2
    block.call(rendered, content)
  elsif block
    block.call(rendered)
  else
    rendered
  end
end

def execute(command, target)
  spawn = POSIX::Spawn::Child.new(*command, :input => target)
  if spawn.status.success?
    spawn.out.gsub("\r", '')
  else
    raise CommandError.new(spawn.err.strip)
  end
end

def initialize(regexp, command, &block)
  super regexp
  @command = command.to_s
  @block = block
end

def render(content)
  rendered = execute(command, content)
  rendered = rendered.to_s.empty? ? content : rendered
  call_block(rendered, content)
end