server.rb

class PostsController

  def create
    @post = Post.new
    @post.title = params[:title]
    @post.save

    redirect "/posts/#{@post.id}" # The show action below.
  end

  def show
    # What is @post in the context of this action 
    # 1. <#Post> - the same one created by #create
    # 2. Nothing.
  end

    # Because we call render view after the main controller action
    # is triggered, self is the instance of the controller, thus
    # we can get access to the instances instance variables when
    # rendering the template
    def render_view
      ERB.new("Hello #{self.instance_variable_get(:@post).name}")
    end
end



# Imagine someone submits a POST request to your App at "/posts"
# Inside Sinatra/Rack/Rails, Imagine some code like this:
request = HTTPRequest.new(:post, "/posts")
# So now we have the raw HTTP Request. 
# We want that to be handled by PostsController#create

# This will be our response
response = PostsController.new

if request.path "/posts" && request.method == :post
  # Pass the request to the instance of the PostsController
  # that will handle the request.
  html = response.create(request).render_view
  
  # After calling that we have the HTML
  # and we send it back to the request object
  # ending the request cycle.
  request.respond_with(html)
elsif request.path.match(/posts\/+d/) && request.method == :get
  html = response.show(request).render_view
  request.respond_with(html)
end