Add support for promoting pawns

app/controllers/pieces_controller.rb

@@ -23,6 +23,12 @@ def valid_moves
     render json: selected_piece.valid_moves
   end
 
+  def promote
+    render(text: 'Piece is not promotable', status: :forbidden) && return unless selected_piece.promotable?
+    selected_piece.promote_to!(params[:type])
+    redirect_to current_game
+  end
+
   private
 
   def authorize_player

app/models/chess_piece.rb

@@ -77,6 +77,10 @@ def load_potential_moves
     potential_moves
   end
 
+  def promotable?
+    false
+  end
+
   private
 
   def move_for(coordinates)

app/models/pawn.rb

@@ -16,11 +16,25 @@ def move_to!(coordinates)
     two_step_move = diff_in_y(coordinates.y) == FIRST_MOVE_FACTOR
     capture_en_passant(coordinates) if game.can_en_passant?(coordinates)
     super
-    game.update(en_passant_position: "#{coordinates.x},#{backward_one(coordinates.y)}") if two_step_move
+    update_en_passant(coordinates) if two_step_move
+    game.update_current_player!(opposite_color) if promotable?
+  end
+
+  def promotable?
+    position_y == 8 || position_y == 1
+  end
+
+  def promote_to!(type)
+    update(type: type)
+    game.update_current_player!(color)
   end
 
   private
 
+  def update_en_passant(coordinates)
+    game.update(en_passant_position: "#{coordinates.x},#{backward_one(coordinates.y)}")
+  end
+
   def capture_en_passant(coordinates)
     game.chess_pieces.find_by(
       position_x: coordinates.x,

config/routes.rb

@@ -2,7 +2,10 @@
   devise_for :users, controllers: { omniauth_callbacks: 'users/omniauth_callbacks' }
   root 'static_pages#index'
   resources :pieces, only: [:show, :update] do
-    get 'valid_moves', on: :member
+    member do
+      get 'valid_moves'
+      put 'promote'
+    end
   end
   resources :users, only: [:show, :update] do
     get '/username', to: 'users#username'

spec/controllers/pieces_controller_spec.rb

@@ -1,34 +1,30 @@
 require 'rails_helper'
 
 RSpec.describe PiecesController, type: :controller do
-  describe 'GET pieces#show' do
-    before do
-      @black_player = create(:user)
-      @game = create(:game, black_player: @black_player)
-    end
+  let(:white_player) { create(:user) }
+  let(:black_player) { create(:user) }
+  let(:game) { create(:game, white_player: white_player, black_player: black_player) }
 
+  describe 'GET pieces#show' do
     it 'responds successfully with an HTTP 200 status code' do
-      sign_in @black_player
-      @game.update_current_player!('white')
-      piece_id = @game.chess_pieces.find_by(position_x: 1, position_y: 7)
+      sign_in black_player
+      game.update_current_player!('white')
+      piece_id = game.chess_pieces.find_by(position_x: 1, position_y: 7)
       get :show, id: piece_id
 
       expect(response).to be_success
       expect(response).to have_http_status(200)
     end
 
     it 'redirects to login if not signed in' do
-      piece_id = @game.chess_pieces.first.id
+      piece_id = game.chess_pieces.first.id
       get :show, id: piece_id
 
       expect(response).to redirect_to new_user_session_path
     end
   end
 
   describe 'PUT pieces#update' do
-    let(:white_player) { create(:user) }
-    let(:game) { create(:game, white_player: white_player) }
-
     it 'responds successfully with an HTTP 302 status code' do
       sign_in white_player
       piece_id = game.chess_pieces.find_by(position_x: 1, position_y: 2).id
@@ -65,8 +61,6 @@
   end
 
   describe 'GET pieces#valid_moves' do
-    let(:game) { create(:game) }
-
     it 'returns valid moves for the piece' do
       pawn = create(:game).chess_pieces.find_by(position_x: 1, position_y: 2)
       sign_in pawn.game.white_player
@@ -86,4 +80,17 @@
       expect(response).to have_http_status(:forbidden)
     end
   end
+
+  describe 'PUT pieces#promote' do
+    it 'promotes the pawn to the specified piece' do
+      sign_in white_player
+      pawn = create(:pawn, position_x: 1, position_y: 8, color: :white, game: game)
+      game.current_player_is_white_player!
+
+      put :promote, id: pawn, type: 'Queen'
+
+      expect(Queen.find(pawn.id)).to be_a Queen
+      expect(game.reload.current_player_is_black_player?).to eq true
+    end
+  end
 end

spec/models/pawn_spec.rb

@@ -98,4 +98,28 @@
       expect(Pawn.find_by(id: pawn.id)).to be_nil
     end
   end
+
+  describe '#promotable?' do
+    it 'is false when not in rank 1 or 8' do
+      pawn = build(:pawn, position_x: 1, position_y: 4)
+
+      expect(pawn.promotable?).to eq false
+    end
+
+    it 'is true when promotion is available' do
+      pawn = build(:pawn, position_x: 1, position_y: 8)
+
+      expect(pawn.promotable?).to eq true
+    end
+  end
+
+  describe '#promote_to!' do
+    it 'promotes the pawn to the specified type' do
+      pawn = build(:pawn, position_x: 1, position_y: 8)
+
+      pawn.promote_to!('Queen')
+
+      expect(pawn.type).to eq 'Queen'
+    end
+  end
 end