Implement unpinning answers

app/controllers/answer_controller.rb

@@ -28,4 +28,14 @@ class AnswerController < ApplicationController
       format.turbo_stream { render "pin", locals: { answer: } }
     end
   end
+
+  def unpin
+    answer = Answer.includes(:user).find(params[:id])
+    UseCase::Answer::Unpin.call(user: current_user, answer:)
+
+    respond_to do |format|
+      format.html { redirect_to(user_path(username: current_user.screen_name)) }
+      format.turbo_stream { render "pin", locals: { answer: } }
+    end
+  end
 end

app/views/actions/_pin.html.haml

@@ -1,5 +1,5 @@
 - if answer.pinned?
-  = button_to pin_answer_path(id: answer.id),
+  = button_to unpin_answer_path(id: answer.id),
     class: "dropdown-item",
     method: :delete,
     form: { id: "ab-pin-#{answer.id}", data: { turbo_stream: true } } do

config/routes.rb

@@ -147,6 +147,7 @@ Rails.application.routes.draw do
   get "/@:username", to: "user#show", as: :user
   get "/@:username/a/:id", to: "answer#show", as: :answer
   post "/@:username/a/:id/pin", to: "answer#pin", as: :pin_answer
+  delete "/@:username/a/:id/pin", to: "answer#unpin", as: :unpin_answer
   get "/@:username/q/:id", to: "question#show", as: :question
   get "/@:username/followers", to: "user#followers", as: :show_user_followers
   get "/@:username/followings", to: "user#followings", as: :show_user_followings

lib/use_case/answer/unpin.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+module UseCase
+  module Answer
+    class Unpin < UseCase::Base
+      option :user, type: Types.Instance(::User)
+      option :answer, type: Types.Instance(::Answer)
+
+      def call
+        check_ownership!
+        check_pinned!
+
+        answer.pinned_at = nil
+        answer.save!
+
+        {
+          status:   200,
+          resource: nil
+        }
+      end
+
+      private
+
+      def check_ownership!
+        raise ::Errors::NotAuthorized unless answer.user == user
+      end
+
+      def check_pinned!
+        raise ::Errors::BadRequest if answer.pinned_at.nil?
+      end
+    end
+  end
+end