asset_paths.rb

require 'active_support/core_ext/file'

module ActionView
  module Helpers

    class AssetPaths #:nodoc:
      attr_reader :config, :controller

      def initialize(config, controller = nil)
        @config = config
        @controller = controller
      end

      # Add the extension +ext+ if not present. Return full or scheme-relative URLs otherwise untouched.
      # Prefix with <tt>/dir/</tt> if lacking a leading +/+. Account for relative URL
      # roots. Rewrite the asset path for cache-busting asset ids. Include
      # asset host, if configured, with the correct request protocol.
      #
      # When include_host is true and the asset host does not specify the protocol
      # the protocol parameter specifies how the protocol will be added.
      # When :relative (default), the protocol will be determined by the client using current protocol
      # When :request, the protocol will be the request protocol
      # Otherwise, the protocol is used (E.g. :http, :https, etc)
      def compute_public_path(source, dir, ext = nil, include_host = true, protocol = nil)
        source = source.to_s
        return source if is_uri?(source)

        source = rewrite_extension(source, dir, ext) if ext
        source = rewrite_asset_path(source, dir)
        source = rewrite_relative_url_root(source, relative_url_root) if has_request?
        source = rewrite_host_and_protocol(source, protocol) if include_host
        source
      end

      # Return the filesystem path for the source
      def compute_source_path(source, dir, ext)
        source = rewrite_extension(source, dir, ext) if ext
        File.join(config.assets_dir, dir, source)
      end

      def is_uri?(path)
        path =~ %r{^[-a-z]+://|^cid:|^//}
      end

    private

      def rewrite_extension(source, dir, ext)
        raise NotImplementedError
      end

      def rewrite_asset_path(source, path = nil)
        raise NotImplementedError
      end

      def rewrite_relative_url_root(source, relative_url_root)
        relative_url_root && !source.starts_with?("#{relative_url_root}/") ? "#{relative_url_root}#{source}" : source
      end

      def has_request?
        controller.respond_to?(:request)
      end

      def rewrite_host_and_protocol(source, protocol = nil)
        host = compute_asset_host(source)
        if host && !is_uri?(host)
          if (protocol || default_protocol) == :request && !has_request?
            host = nil
          else
            host = "#{compute_protocol(protocol)}#{host}"
          end
        end
        host.nil? ? source : "#{host}#{source}"
      end

      def compute_protocol(protocol)
        protocol ||= default_protocol
        case protocol
        when :relative
          "//"
        when :request
          unless @controller
            invalid_asset_host!("The protocol requested was :request. Consider using :relative instead.")
          end
          @controller.request.protocol
        else
          "#{protocol}://"
        end
      end

      def default_protocol
        protocol = @config.action_controller.default_asset_host_protocol if @config.action_controller.present?
        protocol ||= @config.default_asset_host_protocol
        protocol || (has_request? ? :request : :relative)
      end

      def invalid_asset_host!(help_message)
        raise ActionController::RoutingError, "This asset host cannot be computed without a request in scope. #{help_message}"
      end

      # Pick an asset host for this source. Returns +nil+ if no host is set,
      # the host if no wildcard is set, the host interpolated with the
      # numbers 0-3 if it contains <tt>%d</tt> (the number is the source hash mod 4),
      # or the value returned from invoking the proc if it's a proc or the value from
      # invoking call if it's an object responding to call.
      def compute_asset_host(source)
        if host = asset_host_config
          if host.respond_to?(:call)
            args = [source]
            arity = arity_of(host)
            if arity > 1 && !has_request?
              invalid_asset_host!("Remove the second argument to your asset_host Proc if you do not need the request.")
            end
            args << current_request if (arity > 1 || arity < 0) && has_request?
            host.call(*args)
          else
            (host =~ /%d/) ? host % (source.hash % 4) : host
          end
        end
      end

      def relative_url_root
        config = controller.config if controller.respond_to?(:config)
        config ||= config.action_controller if config.action_controller.present?
        config ||= config
        config.relative_url_root
      end

      def asset_host_config
        if config.action_controller.present?
          config.action_controller.asset_host
        else
          config.asset_host
        end
      end

      # Returns the current request if one exists.
      def current_request
        controller.request if has_request?
      end

      # Returns the arity of a callable
      def arity_of(callable)
        callable.respond_to?(:arity) ? callable.arity : callable.method(:call).arity
      end

    end
  end
end