From 0d61f98434b95c754f46c918af5152eda82077cb Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Wed, 24 Jul 2024 08:57:21 +0200
Subject: domain/turn_order: fix a round underflow bug

---
 domain/CMakeLists.txt            |  1 +
 domain/src/turn_order.cpp        |  2 +-
 domain/tests/turn_order_bugs.cpp | 42 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 domain/tests/turn_order_bugs.cpp

(limited to 'domain')

diff --git a/domain/CMakeLists.txt b/domain/CMakeLists.txt
index ec9eb62..6c54e31 100644
--- a/domain/CMakeLists.txt
+++ b/domain/CMakeLists.txt
@@ -41,6 +41,7 @@ add_executable("domain-tests"
 
   "tests/disposition.cpp"
   "tests/participant.cpp"
+  "tests/turn_order_bugs.cpp"
   "tests/turn_order.cpp"
 )
 
diff --git a/domain/src/turn_order.cpp b/domain/src/turn_order.cpp
index e3a1e23..d3140b1 100644
--- a/domain/src/turn_order.cpp
+++ b/domain/src/turn_order.cpp
@@ -122,7 +122,7 @@ namespace turns::domain
     m_data[old_active]->is_active() = false;
     m_data[*m_active]->is_active() = true;
 
-    if (m_active == 0)
+    if (m_active == 0 && m_round_number > 0)
     {
       m_round_number = m_round_number - 1;
     }
diff --git a/domain/tests/turn_order_bugs.cpp b/domain/tests/turn_order_bugs.cpp
new file mode 100644
index 0000000..418a36c
--- /dev/null
+++ b/domain/tests/turn_order_bugs.cpp
@@ -0,0 +1,42 @@
+#include "turns/domain/participant.hpp"
+#include "turns/domain/turn_order.hpp"
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <giomm/liststore.h>
+
+namespace turns::domain::tests
+{
+  /**
+   * Bug description:
+   *
+   * After having stepped according to the step pattern below, tt was possible to step backward often enough to underflow the round number:
+   * - forward
+   * - backward
+   * - forward
+   */
+  SCENARIO("Can step back infinitely", "[turn_order][bug]")
+  {
+    GIVEN("a non-empty turn_order")
+    {
+      auto instance = turn_order::create();
+
+      instance->add("A", 0, disposition::neutral);
+
+      WHEN("it is started and then stepped forward, backward, forward")
+      {
+        instance->start();
+        instance->next();
+        instance->previous();
+        instance->next();
+
+        THEN("it is not possible to step backwards more than once")
+        {
+          instance->previous();
+          instance->previous();
+          REQUIRE(instance->round_number() == 0);
+        }
+      }
+    }
+  }
+}  // namespace turns::domain::tests
\ No newline at end of file
-- 
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