Address review comments from @nilsding

app/controllers/ajax/relationship_controller.rb

@@ -11,7 +11,7 @@ class Ajax::RelationshipController < AjaxController
     params.require :screen_name
 
     UseCase::Relationship::Create.call(
-      current_user: current_user.screen_name,
+      source_user: current_user.screen_name,
       target_user: params[:screen_name],
       type:        params[:type]
     )
@@ -25,7 +25,7 @@ class Ajax::RelationshipController < AjaxController
 
   def destroy
     UseCase::Relationship::Destroy.call(
-      current_user: current_user.screen_name,
+      source_user: current_user.screen_name,
       target_user: params[:screen_name],
       type:        params[:type]
     )

config/routes.rb

@@ -136,11 +136,13 @@ Rails.application.routes.draw do
   match '/@:username/q/:id', to: 'question#show', via: 'get', as: :show_user_question_alt
   match '/@:username/followers(/p/:page)', to: 'user#followers', via: 'get', as: :show_user_followers_alt, defaults: {page: 1}
   match '/@:username/followings(/p/:page)', to: 'user#followings', via: 'get', as: :show_user_followings_alt, defaults: {page: 1}
+  match '/@:username/friends(/p/:page)', to: redirect('/@%{username}/followings/p/%{page}'), via: 'get', defaults: {page: 1}
   match '/:username(/p/:page)', to: 'user#show', via: 'get', as: :show_user_profile, defaults: {page: 1}
   match '/:username/a/:id', to: 'answer#show', via: 'get', as: :show_user_answer
   match '/:username/q/:id', to: 'question#show', via: 'get', as: :show_user_question
   match '/:username/followers(/p/:page)', to: 'user#followers', via: 'get', as: :show_user_followers, defaults: {page: 1}
   match '/:username/followings(/p/:page)', to: 'user#followings', via: 'get', as: :show_user_followings, defaults: {page: 1}
+  match '/:username/friends(/p/:page)', to: redirect('/%{username}/followings/p/%{page}'), via: 'get', defaults: {page: 1}
   match '/:username/lists(/p/:page)', to: 'user#lists', via: 'get', as: :show_user_lists, defaults: {page: 1}
   match '/:username/questions(/p/:page)', to: 'user#questions', via: 'get', as: :show_user_questions, defaults: {page: 1}
 

db/schema.rb

@@ -323,5 +323,6 @@ ActiveRecord::Schema.define(version: 2022_01_05_171216) do
     t.index ["user_id"], name: "index_users_roles_on_user_id"
   end
 
+  add_foreign_key "mute_rules", "users"
   add_foreign_key "profiles", "users"
 end

lib/use_case/relationship/create.rb

@@ -6,8 +6,8 @@ require "errors"
 module UseCase
   module Relationship
     class Create < UseCase::Base
-      option :current_user, type: Types::Coercible::String
-      option :target_user, type: Types::Coercible::String
+      option :source_user, type: Types::Coercible::String | Types.Instance(User)
+      option :target_user, type: Types::Coercible::String | Types.Instance(User)
       option :type, type: Types::RelationshipTypes
 
       def call
@@ -28,9 +28,9 @@ module UseCase
       private
 
       def find_source_user
-        return current_user if current_user.is_a?(::User)
+        return source_user if source_user.is_a?(::User)
 
-        ::User.find_by!(screen_name: current_user)
+        ::User.find_by!(screen_name: source_user)
       rescue ActiveRecord::RecordNotFound
         raise Errors::UserNotFound
       end

lib/use_case/relationship/destroy.rb

@@ -6,7 +6,7 @@ require "errors"
 module UseCase
   module Relationship
     class Destroy < UseCase::Base
-      option :current_user, type: Types::Coercible::String | Types.Instance(User)
+      option :source_user, type: Types::Coercible::String | Types.Instance(User)
       option :target_user, type: Types::Coercible::String | Types.Instance(User)
       option :type, type: Types::RelationshipTypes
 
@@ -28,12 +28,16 @@ module UseCase
       private
 
       def find_source_user
-        ::User.find_by!(screen_name: current_user)
+        return source_user if source_user.is_a?(::User)
+
+        ::User.find_by!(screen_name: source_user)
       rescue ActiveRecord::RecordNotFound
         raise Errors::UserNotFound
       end
 
       def find_target_user
+        return target_user if target_user.is_a?(::User)
+
         ::User.find_by!(screen_name: target_user)
       rescue ActiveRecord::RecordNotFound
         raise Errors::UserNotFound

spec/lib/use_case/relationship/create_spec.rb

@@ -7,8 +7,8 @@ require "errors"
 
 describe UseCase::Relationship::Create do
   shared_examples_for "valid relationship type" do
-    context "current_user does not exist" do
-      let(:current_user) { "Schweinsbraten" }
+    context "source_user does not exist" do
+      let(:source_user) { "Schweinsbraten" }
 
       include_examples "raises an error", Errors::UserNotFound
     end
@@ -19,13 +19,13 @@ describe UseCase::Relationship::Create do
       include_examples "raises an error", Errors::UserNotFound
     end
 
-    context "target_user is current_user" do
+    context "target_user is source_user" do
       let(:target_user)  { user1.screen_name }
 
       include_examples "raises an error", Errors::SelfAction
     end
 
-    context "target_user is different from current_user" do
+    context "target_user is different from source_user" do
       its([:status]) { is_expected.to eq(201) }
       its([:extra])  { is_expected.to eq(target_user: user2) }
 
@@ -40,13 +40,13 @@ describe UseCase::Relationship::Create do
 
   let(:base_params) do
     {
-      current_user: current_user,
+      source_user: source_user,
       target_user:  target_user,
       type:         type
     }
   end
   let(:params)          { base_params }
-  let(:current_user)    { user1.screen_name }
+  let(:source_user)    { user1.screen_name }
   let(:target_user)     { user2.screen_name }
   let(:type)            { nil }
 

spec/lib/use_case/relationship/destroy_spec.rb

@@ -26,15 +26,15 @@ describe UseCase::Relationship::Destroy do
       end
     end
 
-    context "current_user does not exist" do
-      let(:current_user) { "Schweinsbraten" }
+    context "source_user does not exist" do
+      let(:source_user) { "Schweinsbraten" }
       let(:target_user) { user2.screen_name }
 
       include_examples "raises an error", Errors::UserNotFound
     end
 
     context "target_user does not exist" do
-      let(:current_user) { user1.screen_name }
+      let(:source_user) { user1.screen_name }
       let(:target_user) { "peterwitzig" }
 
       include_examples "raises an error", Errors::UserNotFound
@@ -43,13 +43,13 @@ describe UseCase::Relationship::Destroy do
 
   let(:base_params) do
     {
-      current_user: current_user,
+      source_user: source_user,
       target_user:  target_user,
       type:         type
     }
   end
   let(:params)          { base_params }
-  let(:current_user)    { user1.screen_name }
+  let(:source_user)    { user1.screen_name }
   let(:target_user)     { user2.screen_name }
   let(:type)            { nil }