src/derails/action_controller/metal/mime_responds.rb
# frozen_string_literal: true

# :markup: markdown

require "abstract_controller/collector"

module ActionController # :nodoc:
  module MimeResponds
    # Without web-service support, an action which collects the data for displaying
    # a list of people might look something like this:
    #
    #     def index
    #       @people = Person.all
    #     end
    #
    # That action implicitly responds to all formats, but formats can also be
    # explicitly enumerated:
    #
    #     def index
    #       @people = Person.all
    #       respond_to :html, :js
    #     end
    #
    # Here's the same action, with web-service support baked in:
    #
    #     def index
    #       @people = Person.all
    #
    #       respond_to do |format|
    #         format.html
    #         format.js
    #         format.xml { render xml: @people }
    #       end
    #     end
    #
    # What that says is, "if the client wants HTML or JS in response to this action,
    # just respond as we would have before, but if the client wants XML, return them
    # the list of people in XML format." (Rails determines the desired response
    # format from the HTTP Accept header submitted by the client.)
    #
    # Supposing you have an action that adds a new person, optionally creating their
    # company (by name) if it does not already exist, without web-services, it might
    # look like this:
    #
    #     def create
    #       @company = Company.find_or_create_by(name: params[:company][:name])
    #       @person  = @company.people.create(params[:person])
    #
    #       redirect_to(person_list_url)
    #     end
    #
    # Here's the same action, with web-service support baked in:
    #
    #     def create
    #       company  = params[:person].delete(:company)
    #       @company = Company.find_or_create_by(name: company[:name])
    #       @person  = @company.people.create(params[:person])
    #
    #       respond_to do |format|
    #         format.html { redirect_to(person_list_url) }
    #         format.js
    #         format.xml  { render xml: @person.to_xml(include: @company) }
    #       end
    #     end
    #
    # If the client wants HTML, we just redirect them back to the person list. If
    # they want JavaScript, then it is an Ajax request and we render the JavaScript
    # template associated with this action. Lastly, if the client wants XML, we
    # render the created person as XML, but with a twist: we also include the
    # person's company in the rendered XML, so you get something like this:
    #
    #     <person>
    #       <id>...</id>
    #       ...
    #       <company>
    #         <id>...</id>
    #         <name>...</name>
    #         ...
    #       </company>
    #     </person>
    #
    # Note, however, the extra bit at the top of that action:
    #
    #     company  = params[:person].delete(:company)
    #     @company = Company.find_or_create_by(name: company[:name])
    #
    # This is because the incoming XML document (if a web-service request is in
    # process) can only contain a single root-node. So, we have to rearrange things
    # so that the request looks like this (url-encoded):
    #
    #     person[name]=...&person[company][name]=...&...
    #
    # And, like this (xml-encoded):
    #
    #     <person>
    #       <name>...</name>
    #       <company>
    #         <name>...</name>
    #       </company>
    #     </person>
    #
    # In other words, we make the request so that it operates on a single entity's
    # person. Then, in the action, we extract the company data from the request,
    # find or create the company, and then create the new person with the remaining
    # data.
    #
    # Note that you can define your own XML parameter parser which would allow you
    # to describe multiple entities in a single request (i.e., by wrapping them all
    # in a single root node), but if you just go with the flow and accept Rails'
    # defaults, life will be much easier.
    #
    # If you need to use a MIME type which isn't supported by default, you can
    # register your own handlers in `config/initializers/mime_types.rb` as follows.
    #
    #     Mime::Type.register "image/jpeg", :jpg
    #
    # `respond_to` also allows you to specify a common block for different formats
    # by using `any`:
    #
    #     def index
    #       @people = Person.all
    #
    #       respond_to do |format|
    #         format.html
    #         format.any(:xml, :json) { render request.format.to_sym => @people }
    #       end
    #     end
    #
    # In the example above, if the format is xml, it will render:
    #
    #     render xml: @people
    #
    # Or if the format is json:
    #
    #     render json: @people
    #
    # `any` can also be used with no arguments, in which case it will be used for
    # any format requested by the user:
    #
    #     respond_to do |format|
    #       format.html
    #       format.any { redirect_to support_path }
    #     end
    #
    # Formats can have different variants.
    #
    # The request variant is a specialization of the request format, like `:tablet`,
    # `:phone`, or `:desktop`.
    #
    # We often want to render different html/json/xml templates for phones, tablets,
    # and desktop browsers. Variants make it easy.
    #
    # You can set the variant in a `before_action`:
    #
    #     request.variant = :tablet if /iPad/.match?(request.user_agent)
    #
    # Respond to variants in the action just like you respond to formats:
    #
    #     respond_to do |format|
    #       format.html do |variant|
    #         variant.tablet # renders app/views/projects/show.html+tablet.erb
    #         variant.phone { extra_setup; render ... }
    #         variant.none  { special_setup } # executed only if there is no variant set
    #       end
    #     end
    #
    # Provide separate templates for each format and variant:
    #
    #     app/views/projects/show.html.erb
    #     app/views/projects/show.html+tablet.erb
    #     app/views/projects/show.html+phone.erb
    #
    # When you're not sharing any code within the format, you can simplify defining
    # variants using the inline syntax:
    #
    #     respond_to do |format|
    #       format.js         { render "trash" }
    #       format.html.phone { redirect_to progress_path }
    #       format.html.none  { render "trash" }
    #     end
    #
    # Variants also support common `any`/`all` block that formats have.
    #
    # It works for both inline:
    #
    #     respond_to do |format|
    #       format.html.any   { render html: "any"   }
    #       format.html.phone { render html: "phone" }
    #     end
    #
    # and block syntax:
    #
    #     respond_to do |format|
    #       format.html do |variant|
    #         variant.any(:tablet, :phablet){ render html: "any" }
    #         variant.phone { render html: "phone" }
    #       end
    #     end
    #
    # You can also set an array of variants:
    #
    #     request.variant = [:tablet, :phone]
    #
    # This will work similarly to formats and MIME types negotiation. If there is no
    # `:tablet` variant declared, the `:phone` variant will be used:
    #
    #     respond_to do |format|
    #       format.html.none
    #       format.html.phone # this gets rendered
    #     end
    def respond_to(*mimes)
      raise ArgumentError, "respond_to takes either types or a block, never both" if mimes.any? && block_given?

      collector = Collector.new(mimes, request.variant)
      yield collector if block_given?

      if format = collector.negotiate_format(request)
        if media_type && media_type != format
          raise ActionController::RespondToMismatchError
        end
        _process_format(format)
        _set_rendered_content_type(format) unless collector.any_response?
        response = collector.response
        response.call if response
      else
        raise ActionController::UnknownFormat
      end
    end

    # A container for responses available from the current controller for requests
    # for different mime-types sent to a particular action.
    #
    # The public controller methods `respond_to` may be called with a block that is
    # used to define responses to different mime-types, e.g. for `respond_to` :
    #
    #     respond_to do |format|
    #       format.html
    #       format.xml { render xml: @people }
    #     end
    #
    # In this usage, the argument passed to the block (`format` above) is an
    # instance of the ActionController::MimeResponds::Collector class. This object
    # serves as a container in which available responses can be stored by calling
    # any of the dynamically generated, mime-type-specific methods such as `html`,
    # `xml` etc on the Collector. Each response is represented by a corresponding
    # block if present.
    #
    # A subsequent call to #negotiate_format(request) will enable the Collector to
    # determine which specific mime-type it should respond with for the current
    # request, with this response then being accessible by calling #response.
    class Collector
      include AbstractController::Collector
      attr_accessor :format

      def initialize(mimes, variant = nil)
        @responses = {}
        @variant = variant

        mimes.each { |mime| @responses[Mime[mime]] = nil }
      end

      def any(*args, &block)
        if args.any?
          args.each { |type| send(type, &block) }
        else
          custom(Mime::ALL, &block)
        end
      end
      alias :all :any

      def custom(mime_type, &block)
        mime_type = Mime::Type.lookup(mime_type.to_s) unless mime_type.is_a?(Mime::Type)
        @responses[mime_type] ||= if block_given?
          block
        else
          VariantCollector.new(@variant)
        end
      end

      def any_response?
        !@responses.fetch(format, false) && @responses[Mime::ALL]
      end

      def response
        response = @responses.fetch(format, @responses[Mime::ALL])
        if response.is_a?(VariantCollector) # `format.html.phone` - variant inline syntax
          response.variant
        elsif response.nil? || response.arity == 0 # `format.html` - just a format, call its block
          response
        else # `format.html{ |variant| variant.phone }` - variant block syntax
          variant_collector = VariantCollector.new(@variant)
          response.call(variant_collector) # call format block with variants collector
          variant_collector.variant
        end
      end

      def negotiate_format(request)
        @format = request.negotiate_mime(@responses.keys)
      end

      class VariantCollector # :nodoc:
        def initialize(variant = nil)
          @variant = variant
          @variants = {}
        end

        def any(*args, &block)
          if block_given?
            if args.any? && args.none? { |a| a == @variant }
              args.each { |v| @variants[v] = block }
            else
              @variants[:any] = block
            end
          end
        end
        alias :all :any

        def method_missing(name, *, &block)
          @variants[name] = block if block_given?
        end

        def variant
          if @variant.empty?
            @variants[:none] || @variants[:any]
          else
            @variants[variant_key]
          end
        end

        private
          def variant_key
            @variant.find { |variant| @variants.key?(variant) } || :any
          end
      end
    end
  end
end
