Move next_trade to matcher implementation

lib/rex/book/limit_order_book.rb

@@ -8,7 +8,6 @@ module Rex
         @sell_side = RBTree.new
         @buy_side = RBTree.new
         @order_ids = {} # order_id => order
-        @current_trade_id = 0
         @current_order_id = 0
       end
 
@@ -68,10 +67,6 @@ module Rex
         sell_side.first&.[](0)
       end
 
-      def next_trade_id
-        @current_trade_id += 1
-      end
-
       private
 
       attr_reader(

lib/rex/book/matcher.rb

@@ -1,6 +1,10 @@
 module Rex
   module Book
     class Matcher
+      def initialize
+        @current_trade_id = 0
+      end
+
       def match(order_book)
         trades = []
         highest_buy_order = order_book.highest_buy_order
@@ -10,7 +14,7 @@ module Rex
         while highest_buy_order.price >= lowest_sell_order.price
           max_quantity = min(highest_buy_order.remaining_quantity, lowest_sell_order.remaining_quantity)
           trade = Trade.new(
-            id: order_book.next_trade_id,
+            id: next_trade_id,
             buy_order: highest_buy_order,
             sell_order: lowest_sell_order,
             quantity: max_quantity,
@@ -32,6 +36,10 @@ module Rex
 
       private
 
+      def next_trade_id
+        @current_trade_id += 1
+      end
+
       def min(a, b)
         return a if a < b
         b

spec/book/limit_order_book_spec.rb

@@ -150,12 +150,4 @@ RSpec.describe Rex::Book::LimitOrderBook do
       end
     end
   end
-
-  describe "#next_trade_id" do
-    it "returns an increasing trade id" do
-      expect(instance.next_trade_id).to eq(1)
-      expect(instance.next_trade_id).to eq(2)
-      expect(instance.next_trade_id).to eq(3)
-    end
-  end
 end