How to use DSL metaprogramming with Sinatra

Question

I'm trying to work on a DSL to manage different locales within the same route, like get "/test". The

This is an exercise to learn how to extend Sinatra, therefore Rack::Locale or a similar tool is not a valid answer.

Based on the body of the request JSON body, assuming I receive JSON as POST or PUT, I want to respond with the specific locale.

I currently have a barebones script, of what I think I need:

class Locale
  attr_reader :locale_id
  attr_reader :described_class

  alias :current_locale :locale_id

  def initialize(locale_id, &block)
    @locale_id = locale_id
    instance_eval &block
  end

end

def locale(locale_id, &block)
  Locale.new(locale_id, &block)
end

I am missing the capability to respond based on the locale in the request.body JSON I receive as input, and the class here has something else I do not yet see that is needed or is missing.

An example of how this would get used would be:

get '/' do 
   locale 'cs-CS' do 
     "Czech"
     #or db query or string
   end 
   locale 'en-UK' do 
     "British english"
     #or db query or string
   end
end

Therefore to try to clarify even more clearly I will try with a TDD approach:

As User when I send a JSON that contains: "locale": "cs-CS" the result is Czech.

Answer 1

Have you read Extending The DSL and the Conditions section of the README?

Right now, you're not really extending the DSL. I'd redesign it slightly, because it looks like you'd want to match on a case statement but that would mean creating lots of classes or an ugly matching statement. But, Sinatra already has some really nice ways to match on routes and conditions. So, something like this would be more idiomatic:

post '/', :locale => "Czech" do
  "Czech"
end

post '/', :locale => "British English" do
  "British"
end

or

post '/', :locale => "en-GB" do
  "cs-CS"
end

post '/', :locale => "cs-CS" do
  "cs-CS"
end

How to do this? First, you'll need a filter to transform the JSON coming in:

before do
  if request.media_type == "application/json"
    request.body.rewind
    @json = JSON.parse request.body.read
    @locale = @json["locale"] && Locales[@json["locale"]]
  end
end

and then you'll need a condition to check against:

set(:locale) {|value|
  condition {
    !!@locale && (@locale == value || @json["locale"] == value)
  }
}

All together (app.rb):

require 'sinatra'

Locales = {
  'cs-CS' => "Czech",
  'en-GB' => "British English"
}

before do
  if request.media_type == "application/json"
    request.body.rewind
    @json = JSON.parse request.body.read
    @locale = @json["locale"] && Locales[@json["locale"]]
  end
end


set(:locale) {|value|
  condition {
    !!@locale && (@locale == value || @json["locale"] == value)
  }
}


post '/', :locale => "en-GB" do
  "cs-CS"
end


post '/', :locale => "cs-CS" do
  "cs-CS"
end

That works but it won't work as an extension. So, relying the docs I posted at the top:

require 'sinatra/base'

module Sinatra
  module Localiser

    Locales = {
      'cs-CS' => "Czech",
      'en-GB' => "British English"
    }

    def localise!(locales=Locales)
      before do
        if request.media_type == "application/json"
          request.body.rewind
          @json = JSON.parse request.body.read
          @locale = @json["locale"] && locales[@json["locale"]]
        end
      end

      set(:locale) {|value|
        condition {
          !!@locale && (@locale == value || @json["locale"] == value)
        }
      }
    end
  end
  register Localiser
end

Now it will extend the DSL. For example:

require "sinatra/localiser"
class Localised < Sinatra::Base
  register Sinatra::Localiser

  localise!


  post '/', :locale => "Czech" do
    "Czech"
  end


  post '/', :locale => "British English" do
    "British"
  end


  ["get","post"].each{|verb|
    send verb, "/*" do
      "ELSE"
    end
  }

  run! if app_file == $0
end

Hopefully that helps clarify a few things for you.