Rack API versioner.rb

# USAGE ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# require 'rack/versioner'

# V1 = Proc.new do |env|
#   body = "Hello world from V1"
#   [200, {"Content-Type" => "text/html", "Content-Length" => body.size.to_s}, [body]]
# end
# 
# V2 = Proc.new do |env|
#   body = "Hello world from V2"
#   [200, {"Content-Type" => "text/html", "Content-Length" => body.size.to_s}, [body]]
# end
# 
# api = Rack::Versioner.build(:namespace => '/api', :author => 'Ismael Celis') do |m|
#   m.version 'v1', V1
#   m.version 'v2', V2
#   m.current 'v1'
# end
# 
# run api
#
# This gives you
# /api/v1
# /api/v2
# /api/current => same as v1
#

module Rack
  module Versioner
    
    def self.build(options = {}, &block)
      namespace = options.fetch(:namespace, '/api')
      author = options[:author]
      
      builder = Rack::Builder.new
      versioner = Rack::Versioner::Map.new
      
      yield versioner
      
      versioner.versions.each do |num, app|
        builder.map "#{namespace}/#{num}" do
          use Headers, :version => num, :author => author
          run app
        end
      end
      
      # default
      builder.map "#{namespace}/current" do
        use Headers, :version => versioner.current_version, :author => author
        run versioner.current_app
      end
      
      builder
    end
    
    class Headers
      def initialize(app, opts = {})
        @app = app
        @version = opts[:version]
        @author = opts[:author]
      end
      
      def call(env)
        status, headers, body = @app.call(env)
        body = [] if env['REQUEST_METHOD'] == 'HEAD'
        headers["X-API-Version"] = @version.to_s if @version
        headers["X-API-Author"] = @author.to_s if @author
        [status, headers, body]
      end
      
    end
    
    
    class Map
      
      attr_reader :versions
      
      def initialize
        @versions = {}
        @current = nil
      end
      
      def version(num, app)
        @versions[num] = app
        self
      end
      
      def current(num)
        @current = num
        self
      end
      
      def current_version
        @versions[@current] ? @current : @versions.keys.last
      end
      
      def current_app
        @versions[current_version]
      end
      
    end
  end 
end