module ActionDispatch
  module Routing
    # In <tt>config/routes.rb</tt> you define URL-to-controller mappings, but the reverse
    # is also possible: an URL can be generated from one of your routing definitions.
    # URL generation functionality is centralized in this module.
    #
    # See ActionDispatch::Routing for general information about routing and routes.rb.
    #
    # <b>Tip:</b> If you need to generate URLs from your models or some other place,
    # then ActionController::UrlFor is what you're looking for. Read on for
    # an introduction. In general, this module should not be included on its own,
    # as it is usually included by url_helpers (as in Rails.application.routes.url_helpers).
    #
    # == URL generation from parameters
    #
    # As you may know, some functions, such as ActionController::Base#url_for
    # and ActionView::Helpers::UrlHelper#link_to, can generate URLs given a set
    # of parameters. For example, you've probably had the chance to write code
    # like this in one of your views:
    #
    #   <%= link_to('Click here', controller: 'users',
    #           action: 'new', message: 'Welcome!') %>
    #   # => <a href="/users/new?message=Welcome%21">Click here</a>
    #
    # link_to, and all other functions that require URL generation functionality,
    # actually use ActionController::UrlFor under the hood. And in particular,
    # they use the ActionController::UrlFor#url_for method. One can generate
    # the same path as the above example by using the following code:
    #
    #   include UrlFor
    #   url_for(controller: 'users',
    #           action: 'new',
    #           message: 'Welcome!',
    #           only_path: true)
    #   # => "/users/new?message=Welcome%21"
    #
    # Notice the <tt>only_path: true</tt> part. This is because UrlFor has no
    # information about the website hostname that your Rails app is serving. So if you
    # want to include the hostname as well, then you must also pass the <tt>:host</tt>
    # argument:
    #
    #   include UrlFor
    #   url_for(controller: 'users',
    #           action: 'new',
    #           message: 'Welcome!',
    #           host: 'www.example.com')
    #   # => "http://www.example.com/users/new?message=Welcome%21"
    #
    # By default, all controllers and views have access to a special version of url_for,
    # that already knows what the current hostname is. So if you use url_for in your
    # controllers or your views, then you don't need to explicitly pass the <tt>:host</tt>
    # argument.
    #
    # For convenience reasons, mailers provide a shortcut for ActionController::UrlFor#url_for.
    # So within mailers, you only have to type +url_for+ instead of 'ActionController::UrlFor#url_for'
    # in full. However, mailers don't have hostname information, and you still have to provide
    # the +:host+ argument or set the default host that will be used in all mailers using the
    # configuration option +config.action_mailer.default_url_options+. For more information on
    # url_for in mailers read the ActionMailer#Base documentation.
    #
    #
    # == URL generation for named routes
    #
    # UrlFor also allows one to access methods that have been auto-generated from
    # named routes. For example, suppose that you have a 'users' resource in your
    # <tt>config/routes.rb</tt>:
    #
    #   resources :users
    #
    # This generates, among other things, the method <tt>users_path</tt>. By default,
    # this method is accessible from your controllers, views and mailers. If you need
    # to access this auto-generated method from other places (such as a model), then
    # you can do that by including Rails.application.routes.url_helpers in your class:
    #
    #   class User < ActiveRecord::Base
    #     include Rails.application.routes.url_helpers
    #
    #     def base_uri
    #       user_path(self)
    #     end
    #   end
    #
    #   User.find(1).base_uri # => "/users/1"
    #
    module UrlFor
      extend ActiveSupport::Concern
      include PolymorphicRoutes

      included do
        unless method_defined?(:default_url_options)
          # Including in a class uses an inheritable hash. Modules get a plain hash.
          if respond_to?(:class_attribute)
            class_attribute :default_url_options
          else
            mattr_writer :default_url_options
          end

          self.default_url_options = {}
        end

        include(*_url_for_modules) if respond_to?(:_url_for_modules)
      end

      def initialize(*)
        @_routes = nil
        super
      end

      # Hook overridden in controller to add request information
      # with `default_url_options`. Application logic should not
      # go into url_options.
      def url_options
        default_url_options
      end

      # Generate a url based on the options provided, default_url_options and the
      # routes defined in routes.rb. The following options are supported:
      #
      # * <tt>:only_path</tt> - If true, the relative url is returned. Defaults to +false+.
      # * <tt>:protocol</tt> - The protocol to connect to. Defaults to 'http'.
      # * <tt>:host</tt> - Specifies the host the link should be targeted at.
      #   If <tt>:only_path</tt> is false, this option must be
      #   provided either explicitly, or via +default_url_options+.
      # * <tt>:subdomain</tt> - Specifies the subdomain of the link, using the +tld_length+
      #   to split the subdomain from the host.
      #   If false, removes all subdomains from the host part of the link.
      # * <tt>:domain</tt> - Specifies the domain of the link, using the +tld_length+
      #   to split the domain from the host.
      # * <tt>:tld_length</tt> - Number of labels the TLD id composed of, only used if
      #   <tt>:subdomain</tt> or <tt>:domain</tt> are supplied. Defaults to
      #   <tt>ActionDispatch::Http::URL.tld_length</tt>, which in turn defaults to 1.
      # * <tt>:port</tt> - Optionally specify the port to connect to.
      # * <tt>:anchor</tt> - An anchor name to be appended to the path.
      # * <tt>:trailing_slash</tt> - If true, adds a trailing slash, as in "/archive/2009/"
      # * <tt>:script_name</tt> - Specifies application path relative to domain root. If provided, prepends application path.
      #
      # Any other key (<tt>:controller</tt>, <tt>:action</tt>, etc.) given to
      # +url_for+ is forwarded to the Routes module.
      #
      #    url_for controller: 'tasks', action: 'testing', host: 'somehost.org', port: '8080'
      #    # => 'http://somehost.org:8080/tasks/testing'
      #    url_for controller: 'tasks', action: 'testing', host: 'somehost.org', anchor: 'ok', only_path: true
      #    # => '/tasks/testing#ok'
      #    url_for controller: 'tasks', action: 'testing', trailing_slash: true
      #    # => 'http://somehost.org/tasks/testing/'
      #    url_for controller: 'tasks', action: 'testing', host: 'somehost.org', number: '33'
      #    # => 'http://somehost.org/tasks/testing?number=33'
      #    url_for controller: 'tasks', action: 'testing', host: 'somehost.org', script_name: "/myapp"
      #    # => 'http://somehost.org/myapp/tasks/testing'
      #    url_for controller: 'tasks', action: 'testing', host: 'somehost.org', script_name: "/myapp", only_path: true
      #    # => '/myapp/tasks/testing'
      #
      # Missing routes keys may be filled in from the current request's parameters
      # (e.g. +:controller+, +:action+, +:id+ and any other parameters that are
      # placed in the path). Given that the current action has been reached
      # through `GET /users/1`:
      #
      #   url_for(only_path: true)                        # => '/users/1'
      #   url_for(only_path: true, action: 'edit')        # => '/users/1/edit'
      #   url_for(only_path: true, action: 'edit', id: 2) # => '/users/2/edit'
      #
      # Notice that no +:id+ parameter was provided to the first +url_for+ call
      # and the helper used the one from the route's path. Any path parameter
      # implicitly used by +url_for+ can always be overwritten like shown on the
      # last +url_for+ calls.
      def url_for(options = nil)
        case options
        when nil
          _routes.url_for(url_options.symbolize_keys)
        when Hash
          route_name = options.delete :use_route
          _routes.url_for(options.symbolize_keys.reverse_merge!(url_options),
                         route_name)
        when ActionController::Parameters
          route_name = options.delete :use_route
          _routes.url_for(options.to_unsafe_h.symbolize_keys.
                          reverse_merge!(url_options), route_name)
        when String
          options
        when Symbol
          HelperMethodBuilder.url.handle_string_call self, options
        when Array
          components = options.dup
          polymorphic_url(components, components.extract_options!)
        when Class
          HelperMethodBuilder.url.handle_class_call self, options
        else
          HelperMethodBuilder.url.handle_model_call self, options
        end
      end

      protected

      def optimize_routes_generation?
        _routes.optimize_routes_generation? && default_url_options.empty?
      end

      def _with_routes(routes)
        old_routes, @_routes = @_routes, routes
        yield
      ensure
        @_routes = old_routes
      end

      def _routes_context
        self
      end
    end
  end
end