Remove the debug session.

src/Go.cr

@@ -3,6 +3,7 @@ require "kemal"
 require "json"
 
 URL = "localhost"
+PORT = "3000"
 GAME_CACHE = {} of String => Go::Game
 
 def query_game(db, id) : Go::Game?
@@ -116,6 +117,4 @@ ws "/game/:id" do |socket, env|
     end
 end
 
-GAME_CACHE["debug"] = Go::Game.new(Go::Size::Small, "black", "white")
-
 Kemal.run

src/Go/Game.cr

@@ -56,9 +56,60 @@ module Go
             end
         end
 
+        private def count_neighbors(x, y, color, visited)
+            if visited.includes?({x, y}) || (x < 0 || x >= @size.value || y < 0 || y >= @size.value)
+                return 0
+            else
+                visited.push({x, y})
+                case @board[{x, y}]?
+                when color
+                    return count_neighbors(x - 1, y, color, visited) + 
+                        count_neighbors(x + 1, y, color, visited) +
+                        count_neighbors(x, y - 1, color, visited) +
+                        count_neighbors(x, y + 1, color, visited)
+                when nil
+                    return 1
+                else
+                    return 0
+                end
+            end
+            return 0
+        end
+
+        private def remove_color(x, y, color)
+            if !(x < 0 || x >= @size.value || y < 0 || y >= @size.value) && @board[{x, y}]? == color
+                @board.delete({x, y})
+                remove_color(x - 1, y, color)
+                remove_color(x + 1, y, color)
+                remove_color(x, y - 1, color)
+                remove_color(x, y + 1, color)
+            end
+        end
+
+        private def try_remove_branch(x, y, color)
+            if @board[{x, y}]? == color
+                neighbor_count = count_neighbors(x, y, color, [] of Tuple(Int8, Int8))
+                if neighbor_count == 0
+                    remove_color(x, y, color)
+                end
+            end
+        end
+
+        def invert(color)
+            color == Color::Black ? Color::White : Color::Black
+        end
+
         def update(x, y, color)
-            @board[{x, y}] = color
-            @turn = @turn == Color::Black ? Color::White : Color::Black
+            if @turn == color
+                @board[{x, y}] = color
+                new_color = invert(color)
+                try_remove_branch(x - 1, y, new_color)
+                try_remove_branch(x + 1, y, new_color)
+                try_remove_branch(x, y - 1, new_color)
+                try_remove_branch(x, y + 1, new_color)
+                try_remove_branch(x, y, color)
+                @turn = new_color
+            end
         end
 
         private def color_char(color)

src/Go/views/game.ecr

@@ -4,7 +4,7 @@
     var node = document.getElementById('elm-root')
     var app = Elm.Main.embed(node, {
         'black' : <%= black %>,
-        'url' : "<%= "ws://" + URL + ":" + Kemal.config.port.to_s %>",
+        'url' : "<%= "ws://" + URL + ":" + PORT %>",
         'id' : "<%= id %>",
         'size' : <%= size %>
     })