From 966f2a709f6aa4a022c7c13900f97c083ee8a92a Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Thu, 1 Oct 2026 19:30:27 +0200
Subject: kstd: ring_buffer: fix empty() and size()

---
 libs/kstd/kstd/ring_buffer.hpp       | 17 ++++++-----------
 libs/kstd/kstd/ring_buffer.tests.cpp | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/libs/kstd/kstd/ring_buffer.hpp b/libs/kstd/kstd/ring_buffer.hpp
index 92605fc2..48f4da0d 100644
--- a/libs/kstd/kstd/ring_buffer.hpp
+++ b/libs/kstd/kstd/ring_buffer.hpp
@@ -186,7 +186,7 @@ namespace kstd
       }
 
       std::ranges::for_each(std::views::iota(0uz, count), [&](auto i) { m_storage.construct(i); });
-      m_write_index = count % capacity();
+      m_size = count;
     }
 
     //! Construct a ring buffer with a given number of copies of a given value.
@@ -201,7 +201,7 @@ namespace kstd
       }
 
       std::ranges::for_each(std::views::iota(0uz, count), [&](auto i) { m_storage.construct(i, value); });
-      m_write_index = count % capacity();
+      m_size = count;
     }
 
     //! @}
@@ -314,7 +314,7 @@ namespace kstd
     //! @return @p true iff. this ring buffer is empty, @p false otherwise.
     [[nodiscard]] constexpr auto empty() const noexcept -> bool
     {
-      return m_write_index == m_read_index;
+      return m_size == 0;
     }
 
     //! Get the size of this ring buffer.
@@ -322,12 +322,7 @@ namespace kstd
     //! @return The number of elements currently stored in this ring buffer.
     [[nodiscard]] constexpr auto size() const noexcept -> size_type
     {
-      if (m_write_index >= m_read_index)
-      {
-        return m_write_index - m_read_index;
-      }
-
-      return capacity() - (m_read_index - m_write_index);
+      return m_size;
     }
 
     //! Get the maximum number of elements this ring buffer can hold.
@@ -375,8 +370,8 @@ namespace kstd
 
     //! The underlying storage for the elements of this ring buffer.
     bits::basic_storage<value_type, Capacity> m_storage{};
-    //! The index of the next element to be written.
-    size_type m_write_index{};
+    //! The current number of elements in the buffer.
+    size_type m_size{};
     //! The index of the first element to be read.
     size_type m_read_index{};
   };
diff --git a/libs/kstd/kstd/ring_buffer.tests.cpp b/libs/kstd/kstd/ring_buffer.tests.cpp
index a118c2c3..bff8f804 100644
--- a/libs/kstd/kstd/ring_buffer.tests.cpp
+++ b/libs/kstd/kstd/ring_buffer.tests.cpp
@@ -204,6 +204,26 @@ SCENARIO("Ring Buffer initialization and construction", "[kstd][ring_buffer]")
     }
   }
 
+  GIVEN("A full buffer")
+  {
+    auto buffer = kstd::ring_buffer<int, 5>{5};
+
+    THEN("the capacity is 5")
+    {
+      REQUIRE(buffer.capacity() == 5);
+    }
+
+    THEN("the buffer is not empty")
+    {
+      REQUIRE_FALSE(buffer.empty());
+    }
+
+    THEN("the size is equal to the capacity")
+    {
+      REQUIRE(buffer.size() == buffer.capacity());
+    }
+  }
+
   WHEN("constructing by n-value-initialized constructor using a capacity of 5")
   {
     auto buffer = kstd::ring_buffer<int, 5>{3};
-- 
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