Rack basic

Setup

• bundle gem simplemvc #=> simplemvc is gem's name

• In the simplemvc.gemspec, we need to add :

spec.add_runtime_dependency "rack"
# Then remember to run bundle in simplemvc

• And then implement the simplemvc.rb.

require "simplemvc/version"

module Simplemvc
  class Application
    def call(env)
      [200, {"Content-Type" => "text/html"}, ["Hello"]]
      # [http status, header, response]
    end
  end
end

• run gem build simplemvc.gemspec

• Now we can using our gem

• create a directory, in there, blog, then set the Gemfile.

source "https://rubygems.org"

gem "simplemvc", path: "../simplemvc"

• We add the path after gem "simplemvc", because of doing so, we can use simplemvc directly instead building it again everytime we update it.

• Then we set the config.ru in oreder to boot up our blog app by rack.

require './config/application.rb'

run Blog::Application.new

• Then we can run rackup to boot up.

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Routing

• As an example, we need to route /pages/about to the method about in the PageController.

• First, we open our simplemvc.rb, and let's read some codes.

require "simplemvc/version"

module Simplemvc
  class Application

    def call(env)
      # env["PATH_INFO"] = "/pages/about" => PagesController.send(:about)
      controller_class, action = get_controller_and_action(env)
      response = controller_class.new.send(action)
      [200, {"Content-Type" => "text/html"}, [response]]
    end

    def get_controller_and_action(env)
        _, controller_name, action = env["PATH_INFO"].split("/") #=> ['', 
        controller_name = controller_name.capitalize + "Controller"
        [Object.const_get(controller_name), action] 
    end
    
  end
end

• Now we can add PagesController in our blog application.

(app/controllers/pages_controller.rb, semms familiar, right? )

• Here is what pages controller looks like:

class PagesController
  def about
    "about me"
  end
end

• Then we need to make our application know where and what pages controller is. So in the application.rb

require 'simplemvc'

$LOAD_PATH << File.join(File.dirname(__FILE__), "..", "app", "controllers")
require 'pages_controller'
module Blog
  class Application < Simplemvc::Application
    
  end
end

• But now if we go to the route '/' will occur error, we can fix it by do this in simplemvc.rb:

      if env["PATH_INFO"] == "/"
        return [302, {"Location" => "/pages/about"}, []]
      end

Rendering views

• We got to use erubis to render template

• gem install erubis ( in the blog app)

• Then we should add dependency in the simplemvc.gemspec and run bundle

  spec.add_runtime_dependency "erubis"

• In the simplemvc/lib/simplemvc, we create a controller.rb

require "erubis"

module Simplemvc
  class Controller
    def render(view_name, locals = {})
      filename = File.join("app", "views", controller_name, "#{view_name}.erb")
      template = File.read(filename)
      Erubis::Eruby.new(template).result(locals)
    end

    def controller_name
      self.class.to_s.gsub(/Controller$/, "").downcase
    end
  end
end

• Then we should require controller.rb in the simplemvc.rb

require "simplemvc/version"
require "simplemvc/controller.rb"

module Simplemvc
  class Application

    def call(env)
      if env["PATH_INFO"] == "/"
        return [302, {"Location" => "/pages/about"}, []]
      end
      # env["PATH_INFO"] = "/pages/about" => PagesController.send(:about)
      controller_class, action = get_controller_and_action(env)
      response = controller_class.new.send(action)
      [200, {"Content-Type" => "text/html"}, [response]]
    end

    def get_controller_and_action(env)
        _, controller_name, action = env["PATH_INFO"].split("/") #=> ['', 
        controller_name = controller_name.capitalize + "Controller"
        [Object.const_get(controller_name), action] 
    end
    
  end
end

• Finally, we set the PagesController inheritate to Simplemvc::Controller

class PagesController < Simplemvc::Controller
  def about
    "about me"
    render :about, name: "Denny", last_name: "Ku"
  end
end

• Now app/views/pages/about.erb can be accessed

Camelcase constant?

• We need to Open the String class and do some stuffs.

• First in the simplemvc.rb

require "simplemvc/utils.rb"

• Then create the utils.rb

class String
  def to_snake_case
    self.gsub("::", "/").
      gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').        #FOOBar => foo_bar
      gsub(/([a-z\d])([A-Z])/, '\1_\2').       #FO86OBar #=> fo86_o_bar
      tr("-", "_").
      downcase
  end

  def to_camel_case
    return self if self !~ /_/ && self =~ /[A-z]+.*/
    split('_').map{ |str| str.capitalize }.join # hi_there #=> HiThere
  end

end

• Then we change the downcase in controller.rb to to_snake_case

• And capitalize in simplemvc.rb to to_camel_case

• Then it works. We now following the naming convention in Rails.

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Auto Class loding

• If we add the new controller, everytime we must require it in the application.rb

require 'simplemvc'
$LOAD_PATH << File.join(File.dirname(__FILE__), "..", "app", "controllers")
require 'my_pages_controller' # Like this
module Blog
  class Application < Simplemvc::Application
    
  end
end

• We must solve this. First we remvoe the require 'my_pages_controller' in application.rb

• Method missing in ruby:

• If we open pry and input: `Object.const_get(Erubis), we got NameError

class Object
  def self.const_missing(const)
    require const.to_s.downcase
    const
  end
end

Object.const_get(Erubis) #=> Erubis

• By adding the missing method to Object class, we now can require it automatically

• Now, create a dependencies.rb in simplemvc/lib/simplemvc/, and require it in the simplemvc.rb

class Object
  def self.const_missing(const)
    require const.to_s.to_snake_case # remember to use to_snake_case
    Object.const_get(const)  
  end
end

To learn more, you can read: Rails Active Support Source code

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