Refactor federation mappings

The hashes don't work properly with rails 5, there are different classes
loaded when called from the rails engine with missing inheritance.

Also the hashes never worked well with spring.

lib/diaspora/federation/entities.rb

@@ -2,7 +2,7 @@ module Diaspora
   module Federation
     module Entities
       def self.build(entity)
-        public_send(Mappings.builder_for(entity.class), entity)
+        public_send(Mappings.builder_for(entity), entity)
       end
 
       def self.post(post)

lib/diaspora/federation/mappings.rb

@@ -1,82 +1,80 @@
 module Diaspora
   module Federation
     module Mappings
+      # rubocop:disable Metrics/CyclomaticComplexity
+
       # used in Diaspora::Federation::Receive
-      def self.receiver_for(federation_class)
-        fetch_from(ENTITY_RECEIVERS, federation_class)
+      def self.receiver_for(federation_entity)
+        case federation_entity
+        when DiasporaFederation::Entities::Comment           then :comment
+        when DiasporaFederation::Entities::Contact           then :contact
+        when DiasporaFederation::Entities::Conversation      then :conversation
+        when DiasporaFederation::Entities::Like              then :like
+        when DiasporaFederation::Entities::Message           then :message
+        when DiasporaFederation::Entities::Participation     then :participation
+        when DiasporaFederation::Entities::Photo             then :photo
+        when DiasporaFederation::Entities::PollParticipation then :poll_participation
+        when DiasporaFederation::Entities::Profile           then :profile
+        when DiasporaFederation::Entities::Reshare           then :reshare
+        when DiasporaFederation::Entities::StatusMessage     then :status_message
+        else not_found(federation_entity.class)
+        end
       end
 
       # used in Diaspora::Federation::Entities
-      def self.builder_for(diaspora_class)
-        fetch_from(ENTITY_BUILDERS, diaspora_class)
+      def self.builder_for(diaspora_entity)
+        case diaspora_entity
+        when AccountDeletion   then :account_deletion
+        when Comment           then :comment
+        when Contact           then :contact
+        when Conversation      then :conversation
+        when Like              then :like
+        when Message           then :message
+        when Participation     then :participation
+        when Photo             then :photo
+        when PollParticipation then :poll_participation
+        when Profile           then :profile
+        when Reshare           then :reshare
+        when Retraction        then :retraction
+        when ContactRetraction then :retraction
+        when StatusMessage     then :status_message
+        else not_found(diaspora_entity.class)
+        end
       end
 
       def self.model_class_for(entity_name)
-        fetch_from(ENTITY_MODELS, entity_name)
+        case entity_name
+        when "Comment"           then Comment
+        when "Conversation"      then Conversation
+        when "Like"              then Like
+        when "Participation"     then Participation
+        when "PollParticipation" then PollParticipation
+        when "Photo"             then Photo
+        when "Poll"              then Poll
+        when "Post"              then Post
+        when "Person"            then Person # TODO: deprecated
+        when "Reshare"           then Post
+        when "StatusMessage"     then Post
+        else not_found(entity_name)
+        end
       end
 
       def self.entity_name_for(model)
-        fetch_from(ENTITY_NAMES, model.class.base_class)
+        case model
+        when Comment           then "Comment"
+        when Like              then "Like"
+        when Participation     then "Participation"
+        when PollParticipation then "PollParticipation"
+        when Photo             then "Photo"
+        when Post              then "Post"
+        else not_found(model.class)
+        end
       end
+      # rubocop:enable Metrics/CyclomaticComplexity
 
-      private_class_method def self.fetch_from(mapping, key)
-        mapping.fetch(key) { raise DiasporaFederation::Entity::UnknownEntity, "unknown entity: #{key}" }
+      private_class_method def self.not_found(key)
+        raise DiasporaFederation::Entity::UnknownEntity, "unknown entity: #{key}"
       end
-
-      ENTITY_RECEIVERS = {
-        DiasporaFederation::Entities::Comment           => :comment,
-        DiasporaFederation::Entities::Contact           => :contact,
-        DiasporaFederation::Entities::Conversation      => :conversation,
-        DiasporaFederation::Entities::Like              => :like,
-        DiasporaFederation::Entities::Message           => :message,
-        DiasporaFederation::Entities::Participation     => :participation,
-        DiasporaFederation::Entities::Photo             => :photo,
-        DiasporaFederation::Entities::PollParticipation => :poll_participation,
-        DiasporaFederation::Entities::Profile           => :profile,
-        DiasporaFederation::Entities::Reshare           => :reshare,
-        DiasporaFederation::Entities::StatusMessage     => :status_message
-      }.freeze
-
-      ENTITY_BUILDERS = {
-        AccountDeletion   => :account_deletion,
-        Comment           => :comment,
-        Contact           => :contact,
-        Conversation      => :conversation,
-        Like              => :like,
-        Message           => :message,
-        Participation     => :participation,
-        Photo             => :photo,
-        PollParticipation => :poll_participation,
-        Profile           => :profile,
-        Reshare           => :reshare,
-        Retraction        => :retraction,
-        ContactRetraction => :retraction,
-        StatusMessage     => :status_message
-      }.freeze
-
-      ENTITY_MODELS = {
-        "Comment"           => Comment,
-        "Conversation"      => Conversation,
-        "Like"              => Like,
-        "Participation"     => Participation,
-        "PollParticipation" => PollParticipation,
-        "Photo"             => Photo,
-        "Poll"              => Poll,
-        "Post"              => Post,
-        # TODO: deprecated
-        "Person"            => Person,
-        "Reshare"           => Post,
-        "StatusMessage"     => Post
-      }.freeze
-
-      ENTITY_NAMES = {
-        Comment           => "Comment",
-        Like              => "Like",
-        Participation     => "Participation",
-        PollParticipation => "PollParticipation",
-        Photo             => "Photo",
-        Post              => "Post"
-      }.freeze
     end
   end
 end

lib/diaspora/federation/receive.rb

@@ -4,7 +4,7 @@ module Diaspora
       extend Diaspora::Logging
 
       def self.perform(entity)
-        public_send(Mappings.receiver_for(entity.class), entity)
+        public_send(Mappings.receiver_for(entity), entity)
       end
 
       def self.account_deletion(entity)