Extract possible collisions to Utils (#31)

src/strategy/cautious_carol.cr

@@ -10,20 +10,7 @@ class Strategy::CautiousCarol < Strategy::Base
     return RandomValid.new(@context).move if valid_moves[:moves].empty?
 
     # Check for head-to-head collision possibilities
-    dangerous_moves = [] of BattleSnake::Point
-    @context.enemies.each do |snake|
-      next if (snake.head <=> @context.you.head) > 2
-      next if snake.body.size < @context.you.body.size
-
-      # Check if we share valid moves (meeting point for collision)
-      @context.valid_moves(snake.head)[:neighbors].values.each do |point|
-        meeting_point = valid_moves[:neighbors].values.find do |p|
-          (point <=> p).zero?
-        end
-        next if meeting_point.nil?
-        dangerous_moves << point
-      end
-    end
+    dangerous_moves = Utils.possible_collisions(@context)
 
     # Calculate chase closest food direction
     closest_food = ChaseClosestFood.new(@context).move

src/strategy/utils/possible_collisions.cr

@@ -0,0 +1,24 @@
+# Implementation that returns all moves that could cause a collision with
+# another snake which would result in death.
+def Strategy::Utils.possible_collisions(context : BattleSnake::Context)
+  valid_moves = context.valid_moves(context.you.head)
+  dangerous_moves = [] of BattleSnake::Point
+
+  context.enemies.each do |snake|
+    # Snake is too far away to collide
+    next if (snake.head <=> context.you.head) > 2
+    # We're larger than the snake (not dangerous)
+    next if snake.body.size < context.you.body.size
+
+    # Check if we share valid moves (meeting point for collision)
+    context.valid_moves(snake.head)[:neighbors].values.each do |point|
+      meeting_point = valid_moves[:neighbors].values.find do |p|
+        (point <=> p).zero?
+      end
+      next if meeting_point.nil?
+      dangerous_moves << point
+    end
+  end
+
+  dangerous_moves
+end