rails--rails/railties/lib/rails/commands/commands_tasks.rb

module Rails
  # This is a class which takes in a rails command and initiates the appropriate
  # initiation sequence.
  #
  # Warning: This class mutates ARGV because some commands require manipulating
  # it before they are run.
  class CommandsTasks # :nodoc:
    attr_reader :argv

    HELP_MESSAGE = <<-EOT
Usage: rails COMMAND [ARGS]

The most common rails commands are:
 generate    Generate new code (short-cut alias: "g")
 console     Start the Rails console (short-cut alias: "c")
 server      Start the Rails server (short-cut alias: "s")
 dbconsole   Start a console for the database specified in config/database.yml
             (short-cut alias: "db")
 new         Create a new Rails application. "rails new my_app" creates a
             new application called MyApp in "./my_app"

In addition to those, there are:
 application  Generate the Rails application code
 destroy      Undo code generated with "generate" (short-cut alias: "d")
 plugin new   Generates skeleton for developing a Rails plugin
 runner       Run a piece of code in the application environment (short-cut alias: "r")

All commands can be run with -h (or --help) for more information.
EOT

    COMMAND_WHITELIST = %(plugin generate destroy console server dbconsole application runner new version help)

    def initialize(argv)
      @argv = argv
    end

    def run_command!(command)
      command = parse_command(command)
      if COMMAND_WHITELIST.include?(command)
        send(command)
      else
        write_error_message(command)
      end
    end

    def plugin
      require_command!("plugin")
    end

    def generate
      generate_or_destroy(:generate)
    end

    def destroy
      generate_or_destroy(:destroy)
    end

    def console
      require_command!("console")
      options = Rails::Console.parse_arguments(argv)

      # RAILS_ENV needs to be set before config/application is required
      ENV['RAILS_ENV'] = options[:environment] if options[:environment]

      # shift ARGV so IRB doesn't freak
      shift_argv!

      require_application_and_environment!
      Rails::Console.start(Rails.application, options)
    end

    def server
      set_application_directory!
      require_command!("server")

      Rails::Server.new.tap do |server|
        # We need to require application after the server sets environment,
        # otherwise the --environment option given to the server won't propagate.
        require APP_PATH
        Dir.chdir(Rails.application.root)
        server.start
      end
    end

    def dbconsole
      require_command!("dbconsole")
      Rails::DBConsole.start
    end

    def application
      require_command!("application")
    end

    def runner
      require_command!("runner")
    end

    def new
      if %w(-h --help).include?(argv.first)
        require_command!("application")
      else
        exit_with_initialization_warning!
      end
    end

    def version
      argv.unshift '--version'
      require_command!("application")
    end

    def help
      write_help_message
    end

    private

      def exit_with_initialization_warning!
        puts "Can't initialize a new Rails application within the directory of another, please change to a non-Rails directory first.\n"
        puts "Type 'rails' for help."
        exit(1)
      end

      def shift_argv!
        argv.shift if argv.first && argv.first[0] != '-'
      end

      def require_command!(command)
        require "rails/commands/#{command}"
      end

      def generate_or_destroy(command)
        require 'rails/generators'
        require_application_and_environment!
        Rails.application.load_generators
        require "rails/commands/#{command}"
      end

      # Change to the application's path if there is no config.ru file in current directory.
      # This allows us to run `rails server` from other directories, but still get
      # the main config.ru and properly set the tmp directory.
      def set_application_directory!
        Dir.chdir(File.expand_path('../../', APP_PATH)) unless File.exists?(File.expand_path("config.ru"))
      end

      def require_application_and_environment!
        require APP_PATH
        Rails.application.require_environment!
      end

      def write_help_message
        puts HELP_MESSAGE
      end

      def write_error_message(command)
        puts "Error: Command '#{command}' not recognized"
        if %x{rake #{command} --dry-run 2>&1 } && $?.success?
          puts "Did you mean: `$ rake #{command}` ?\n\n"
        end
        write_help_message
        exit(1)
      end

      def parse_command(command)
        case command
        when '--version', '-v'
          'version'
        when '--help', '-h'
          'help'
        else
          command
        end
      end
  end
end