From 2b9c82c4f6bf208a3d6648d7cc13b1f6c1b73616 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tim=20K=C3=A4chele?= <mail@timkaechele.me>
Date: Sun, 29 Oct 2023 00:01:31 +0200
Subject: [PATCH] Add stack overflow based test case for matcher implementation

---
 lib/rex/matcher.rb       |  2 ++
 spec/factories/orders.rb |  1 +
 spec/matcher_spec.rb     | 48 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/lib/rex/matcher.rb b/lib/rex/matcher.rb
index 9fe34f2..bbd6d60 100644
--- a/lib/rex/matcher.rb
+++ b/lib/rex/matcher.rb
@@ -28,6 +28,8 @@ module Rex
 
         return trades if highest_buy_order.nil? || lowest_sell_order.nil?
       end
+
+      trades
     end
 
     private
diff --git a/spec/factories/orders.rb b/spec/factories/orders.rb
index f61c2a0..85fc021 100644
--- a/spec/factories/orders.rb
+++ b/spec/factories/orders.rb
@@ -7,5 +7,6 @@ FactoryBot.define do
     sequence(:is_buy) { |i| (i % 2).zero? }
     sequence(:price) { 100 }
     sequence(:amount) { 20 }
+    remaining_amount { amount }
   end
 end
diff --git a/spec/matcher_spec.rb b/spec/matcher_spec.rb
index c75c8b9..3f504eb 100644
--- a/spec/matcher_spec.rb
+++ b/spec/matcher_spec.rb
@@ -48,5 +48,53 @@ RSpec.describe Rex::Matcher do
         expect(instance.match(Rex::OrderBook.new)).to eq([])
       end
     end
+
+    # https://stackoverflow.com/a/18524231/3200224
+    # Testing a common example with a proven to be correct solution
+    context "stack overflow scenario" do
+      let(:order_1) { build(:order, price: 2030, is_buy: false, amount: 100) }
+      let(:order_2) { build(:order, price: 2025, is_buy: false, amount: 100) }
+      let(:order_3) { build(:order, price: 2030, is_buy: false, amount: 200) }
+      let(:order_4) { build(:order, price: 2015, is_buy: true, amount: 100) }
+      let(:order_5) { build(:order, price: 2020, is_buy: true, amount: 200) }
+      let(:order_6) { build(:order, price: 2015, is_buy: true, amount: 200) }
+
+      let(:crossing_order) { build(:order, is_buy: true, amount: 250, price: 2035) }
+
+      before do
+        order_book.add_order(order_1)
+        order_book.add_order(order_2)
+        order_book.add_order(order_3)
+        order_book.add_order(order_4)
+        order_book.add_order(order_5)
+        order_book.add_order(order_6)
+
+        order_book.add_order(crossing_order)
+      end
+
+      it "matches the orders accordingly" do
+        trades = instance.match(order_book)
+
+        expect(trades.length).to eq(3)
+
+        expect(trades[0].id).to eq(1)
+        expect(trades[0].price).to eq(2025)
+        expect(trades[0].amount).to eq(100)
+        expect(trades[0].buy_order).to eq(crossing_order)
+        expect(trades[0].sell_order).to eq(order_2)
+
+        expect(trades[1].id).to eq(2)
+        expect(trades[1].price).to eq(2030)
+        expect(trades[1].amount).to eq(100)
+        expect(trades[1].buy_order).to eq(crossing_order)
+        expect(trades[1].sell_order).to eq(order_1)
+
+        expect(trades[2].id).to eq(3)
+        expect(trades[2].price).to eq(2030)
+        expect(trades[2].amount).to eq(50)
+        expect(trades[2].buy_order).to eq(crossing_order)
+        expect(trades[2].sell_order).to eq(order_3)
+      end
+    end
   end
 end