console.rb

require 'rack'
require 'rack/console/methods'
require 'rack/console/session'
require 'rack/console/version'

module Rack
  class Console
    def self.start(options = {})
      self.new(options).start
    end

    def initialize(options = {})
      @options = default_options.merge(options)

      ENV['RACK_ENV'] = @options[:environment]
      set_preamble

      $LOAD_PATH.unshift(*@options[:include]) if @options[:include]

      require @options[:require] if @options[:require]
    end

    def start
      puts ENV['RACK_CONSOLE_INTRO'] unless ENV['IGNORE_RACK_CONSOLE_INTRO']

      app = Rack::Builder.parse_file(@options[:config]).first

      # Add convenience methods to the top-level binding (main)
      main.extend(Rack::Console::Methods)
      main.instance_variable_set(:@app, Rack::Console::Session.new(app))

      begin
        require 'pry'
        Pry.start
      rescue LoadError
        require 'irb'
        IRB.start
      end
    end

    private

    def main
      TOPLEVEL_BINDING.eval('self')
    end

    def set_preamble
      return if ENV['RACK_CONSOLE_INTRO']

      loading = "Loading #{ENV['RACK_ENV']} environment"
      version = "(Rack::Console #{Rack::Console::VERSION})"

      ENV['RACK_CONSOLE_INTRO'] = "#{loading} #{version}"
    end

    def default_options
      {
        config: 'config.ru',
        environment: ENV['RACK_ENV'] || 'development'
      }
    end
  end
end