AsciiDoc filter for literate programming-style code blocks.

literate.rb

#!/usr/bin/env ruby

require 'open3'
require 'tmpdir'

module Literate
  class Line
    INDENT = ''.freeze

    def self.indent(str)
      return str if str == ""
      str.gsub(/^/, INDENT)
    end

    def initialize(str)
      @str = str
    end

    def to_s
      @str
    end

    def cd?
      !path.nil?
    end

    def path
      @str[/^#{INDENT}%-? cd (.+)$/, 1]
    end

    def silent?
      @str =~ /^#{INDENT}%- /
    end

    def ignore?
      @str =~ /^#{INDENT}%% /
    end

    def command?
      @str =~ /^#{INDENT}% /
    end

    def plain?
      !silent? && !ignore? && !command?
    end

    def formatted_command
      "#{INDENT}% #{command}\n"
    end

    def command
      @command ||=
        begin
          @str[/^#{INDENT}%[-%]? (.+)$/, 1].gsub /\{\{(.+)\}\}/ do |match|
            Command.capture($1.strip).chomp
          end
        end
    end
  end

  def self.in_masked_tmpdir
    original_directory = Dir.pwd
    new_dir = File.join(Dir.pwd, 'tmp')
    Dir.chdir(new_dir)
    yield(new_dir).gsub(new_dir, "~/examples")
  ensure
    Dir.chdir original_directory
  end

  class LineReader
    include Enumerable

    def initialize(source)
      @source = source
    end

    def each
      @source.each_line do |line|
        yield Line.new(line)
      end
    end
  end

  class Command
    attr_reader :line

    def initialize(line)
      @line = line
    end

    def result
      if line.silent?
        run
        ''
      elsif line.ignore? || line.cd?
        line.formatted_command
      elsif line.command?
        line.formatted_command +
          Line.indent(run)
      else
        line.to_s
      end
    end

    def self.capture(cmd)
      input, output, wait_thr = Open3.popen2e(cmd)
      output.read
    ensure
      input.close
      output.close
    end

    private

    def run
      self.class.capture(line.command)
    end
  end

  def self.literalize(str)
    in_masked_tmpdir do |dir|
      original_directory = dir
      LineReader.new(str).each_with_object('') do |line, output|
        if line.cd?
          dir = File.join(dir, line.path)
          raise "Invalid path: #{dir}" unless dir.start_with?(original_directory)
          Dir.chdir(dir)
        end
        output << Command.new(line).result
      end
    end
  end
end

puts Literate.literalize(STDIN.read)