For learning

rails_router_version_1.rb

require 'action_dispatch/journey/core-ext/hash'
require 'action_dispatch/journey/router/utils'
require 'action_dispatch/journey/router/strexp'
require 'action_dispatch/journey/routes'
require 'action_dispatch/journey/formatter'

before = $-w
$-w = false
require 'action_dispatch/journey/parser'
$-w = before

require 'action_dispatch/journey/route'
require 'action_dispatch/journey/path/pattern'

module ActionDispatch
  module Journey
    class Router
      class RoutingError < ::StandardError
      end

      VERSION = '2.0.0'

      class NullReq # :nodoc:
        attr_reader :env
        def initialize env
          @env = env
        end

        def request_method
          env['REQUEST_METHOD']
        end

        def path_info
          env['PATH_INFO']
        end

        def ip
          env['REMOTE_ADDR']
        end

        def [](k); env[k]; end
      end

      attr_reader :request_class, :formatter
      attr_accessor :routes

      def initialize routes, options
        @options       = options
        @params_key    = options[:parameters_key]
        @request_class = options[:request_class] || NullReq
        @routes        = routes
      end

      def call env
        env['PATH_INFO'] = Utils.normalize_path env['PATH_INFO']

        find_routes(env).each do |match, parameters, route|
          script_name, path_info, set_params = env.values_at('SCRIPT_NAME',
                                                             'PATH_INFO',
                                                             @params_key)

          unless route.path.anchored
            env['SCRIPT_NAME'] = (script_name.to_s + match.to_s).chomp('/')
            env['PATH_INFO']   = match.post_match
          end

          env[@params_key] = (set_params || {}).merge parameters

          status, headers, body = route.app.call(env)

          if 'pass' == headers['X-Cascade']
            env['SCRIPT_NAME'] = script_name
            env['PATH_INFO']   = path_info
            env[@params_key]   = set_params
            next
          end

          return [status, headers, body]
        end

        return [404, {'X-Cascade' => 'pass'}, ['Not Found']]
      end

      def recognize req
        find_routes(req.env).each do |match, parameters, route|
          unless route.path.anchored
            req.env['SCRIPT_NAME'] = match.to_s
            req.env['PATH_INFO']   = match.post_match.sub(/^([^\/])/, '/\1')
          end

          yield(route, nil, parameters)
        end
      end

      def visualizer
        tt     = GTG::Builder.new(ast).transition_table
        groups = partitioned_routes.first.map(&:ast).group_by { |a| a.to_s }
        asts   = groups.values.map { |v| v.first }
        tt.visualizer asts
      end

      private

      def partitioned_routes
        routes.partitioned_routes
      end

      def ast
        routes.ast
      end

      def simulator
        routes.simulator
      end

      def custom_routes
        partitioned_routes.last
      end

      def filter_routes path
        return [] unless ast
        data = simulator.match(path)
        data ? data.memos : []
      end

      def find_routes env
        req = request_class.new env

        routes = filter_routes(req.path_info).concat custom_routes.find_all { |r|
          r.path.match(req.path_info)
        }
        routes.concat get_routes_as_head(routes)

        routes.sort_by!(&:precedence).select! { |r|
          r.constraints.all? { |k,v| v === req.send(k) } &&
            r.verb === req.request_method
        }
        routes.reject! { |r| req.ip && !(r.ip === req.ip) }

        routes.map! { |r|
          match_data  = r.path.match(req.path_info)
          match_names = match_data.names.map { |n| n.to_sym }
          match_values = match_data.captures.map { |v| v && Utils.unescape_uri(v) }
          info = Hash[match_names.zip(match_values).find_all { |_,y| y }]

          [match_data, r.defaults.merge(info), r]
        }
      end

      def get_routes_as_head(routes)
        precedence = (routes.map(&:precedence).max || 0) + 1
        routes = routes.select { |r|
          r.verb === "GET" && !(r.verb === "HEAD")
        }.map! { |r|
          Route.new(r.name,
                    r.app,
                    r.path,
                    r.conditions.merge(:request_method => "HEAD"),
                    r.defaults).tap do |route|
                      route.precedence = r.precedence + precedence
                    end
        }
        routes.flatten!
        routes
      end
    end
  end
end