kstd: ring_buffer: implement [cr][begin|end]()

2 files changed, 180 insertions, 0 deletions

diff --git a/libs/kstd/kstd/ring_buffer.hpp b/libs/kstd/kstd/ring_buffer.hpp
index 48f4da0d..b015755d 100644
--- a/libs/kstd/kstd/ring_buffer.hpp
+++ b/libs/kstd/kstd/ring_buffer.hpp
@@ -296,6 +296,42 @@ namespace kstd
       return std::default_sentinel;
     }
 
+    //! Get a reverse iterator to the first element.
+    [[nodiscard]] constexpr auto rbegin() noexcept -> reverse_iterator
+    {
+      return std::make_reverse_iterator(iterator{this, m_size});
+    }
+
+    //! Get a reverse iterator to the first element.
+    [[nodiscard]] constexpr auto rbegin() const noexcept -> const_reverse_iterator
+    {
+      return std::make_reverse_iterator(const_iterator{this, m_size});
+    }
+
+    //! Get a reverse iterator to the first element.
+    [[nodiscard]] constexpr auto crbegin() const noexcept -> const_reverse_iterator
+    {
+      return std::make_reverse_iterator(const_iterator{this, m_size});
+    }
+
+    //! Get a reverse iterator to the first element.
+    [[nodiscard]] constexpr auto rend() noexcept -> reverse_iterator
+    {
+      return std::make_reverse_iterator(iterator{this, 0});
+    }
+
+    //! Get a reverse iterator to the first element.
+    [[nodiscard]] constexpr auto rend() const noexcept -> const_reverse_iterator
+    {
+      return std::make_reverse_iterator(const_iterator{this, 0});
+    }
+
+    //! Get a reverse iterator to the first element.
+    [[nodiscard]] constexpr auto crend() const noexcept -> const_reverse_iterator
+    {
+      return std::make_reverse_iterator(const_iterator{this, 0});
+    }
+
     //! @}
 
     //! @name Capacity
diff --git a/libs/kstd/kstd/ring_buffer.tests.cpp b/libs/kstd/kstd/ring_buffer.tests.cpp
index bff8f804..84adba91 100644
--- a/libs/kstd/kstd/ring_buffer.tests.cpp
+++ b/libs/kstd/kstd/ring_buffer.tests.cpp
@@ -136,6 +136,21 @@ SCENARIO("Ring Buffer interface types", "[kstd][ring_buffer]")
     {
       STATIC_REQUIRE(std::is_same_v<std::default_sentinel_t, decltype(std::declval<buffer &>().cend())>);
     }
+
+    THEN("the return type of rbegin() is `reverse_iterator`")
+    {
+      STATIC_REQUIRE(std::is_same_v<buffer::reverse_iterator, decltype(std::declval<buffer &>().rbegin())>);
+    }
+
+    THEN("the return type of rbegin() is `const_reverse_iterator` on a const buffer")
+    {
+      STATIC_REQUIRE(std::is_same_v<buffer::const_reverse_iterator, decltype(std::declval<buffer const &>().rbegin())>);
+    }
+
+    THEN("the return type of crbegin() is `const_reverse_iterator`")
+    {
+      STATIC_REQUIRE(std::is_same_v<buffer::const_reverse_iterator, decltype(std::declval<buffer &>().crbegin())>);
+    }
   }
 }
 
@@ -418,6 +433,36 @@ SCENARIO("Ring Buffer iterators", "[kstd][ring_buffer]")
       REQUIRE(std::ranges::distance(buffer) == 0);
     }
 
+    THEN("rbegin() returns an iterator equal to rend()")
+    {
+      REQUIRE(buffer.rbegin() == buffer.rend());
+    }
+
+    THEN("rbegin() returns an iterator equal to crend()")
+    {
+      REQUIRE(buffer.rbegin() == buffer.crend());
+    }
+
+    THEN("crbegin() returns an iterator equal to rend()")
+    {
+      REQUIRE(buffer.crbegin() == buffer.rend());
+    }
+
+    THEN("crbegin() returns an iterator equal to crend()")
+    {
+      REQUIRE(buffer.crbegin() == buffer.crend());
+    }
+
+    THEN("the distance between rbegin() and rend() is 0")
+    {
+      REQUIRE(std::ranges::distance(buffer.rbegin(), buffer.rend()) == 0);
+    }
+
+    THEN("the distance between crbegin() and crend() is 0")
+    {
+      REQUIRE(std::ranges::distance(buffer.crbegin(), buffer.crend()) == 0);
+    }
+
     WHEN("working through a const reference")
     {
       auto const & ref = buffer;
@@ -441,6 +486,16 @@ SCENARIO("Ring Buffer iterators", "[kstd][ring_buffer]")
       {
         REQUIRE(std::ranges::distance(buffer) == 0);
       }
+
+      THEN("rbegin() returns an iterator equal to rend()")
+      {
+        REQUIRE(buffer.rbegin() == buffer.rend());
+      }
+
+      THEN("the distance between rbegin() and rend() is 0")
+      {
+        REQUIRE(std::ranges::distance(buffer.rbegin(), buffer.rend()) == 0);
+      }
     }
   }
 
@@ -503,6 +558,46 @@ SCENARIO("Ring Buffer iterators", "[kstd][ring_buffer]")
       REQUIRE(*buffer.cbegin() == 'a');
     }
 
+    THEN("rbegin() returns an iterator that does not equal rend()")
+    {
+      REQUIRE(buffer.rbegin() != buffer.rend());
+    }
+
+    THEN("rbegin() returns an iterator that does not equal crend()")
+    {
+      REQUIRE(buffer.rbegin() != buffer.crend());
+    }
+
+    THEN("the distance between rbegin() and rend() is 3")
+    {
+      REQUIRE(std::ranges::distance(buffer.rbegin(), buffer.rend()) == 3);
+    }
+
+    THEN("the distance between crbegin() and crend() is 3")
+    {
+      REQUIRE(std::ranges::distance(buffer.crbegin(), buffer.crend()) == 3);
+    }
+
+    THEN("rbegin() returns an iterator to the first element")
+    {
+      REQUIRE(*buffer.rbegin() == 'a');
+    }
+
+    THEN("crbegin() returns an iterator that does not equal rend()")
+    {
+      REQUIRE(buffer.crbegin() != buffer.rend());
+    }
+
+    THEN("crbegin() returns an iterator that does not equal crend()")
+    {
+      REQUIRE(buffer.crbegin() != buffer.crend());
+    }
+
+    THEN("crbegin() returns an iterator to the first element")
+    {
+      REQUIRE(*buffer.crbegin() == 'a');
+    }
+
     THEN(
         "incrementing the iterator returned by begin() past the end, yields an iterator equal to std::default_sentinel")
     {
@@ -565,6 +660,45 @@ SCENARIO("Ring Buffer iterators", "[kstd][ring_buffer]")
       REQUIRE(it == buffer.cend());
     }
 
+    THEN("incrementing the iterator returned by rbegin() past the end, yields an iterator equal to rend()")
+    {
+      auto it = buffer.rbegin();
+      ++it;
+      ++it;
+      ++it;
+
+      REQUIRE(it == buffer.rend());
+    }
+
+    THEN("incrementing the iterator returned by rbegin() past the end, yields an iterator equal to crend()")
+    {
+      auto it = buffer.rbegin();
+      ++it;
+      ++it;
+      ++it;
+
+      REQUIRE(it == buffer.crend());
+    }
+
+    THEN("incrementing the iterator returned by crbegin() past the end, yields an iterator equal to rend()")
+    {
+      auto it = buffer.crbegin();
+      ++it;
+      ++it;
+      ++it;
+
+      REQUIRE(it == buffer.rend());
+    }
+
+    THEN("incrementing the iterator returned by crbegin() past the end, yields an iterator equal to crend()")
+    {
+      auto it = buffer.crbegin();
+      ++it;
+      ++it;
+      ++it;
+
+      REQUIRE(it == buffer.crend());
+    }
     WHEN("working through a const reference")
     {
       auto const & ref = buffer;
@@ -614,6 +748,16 @@ SCENARIO("Ring Buffer iterators", "[kstd][ring_buffer]")
 
         REQUIRE(it == ref.end());
       }
+
+      THEN("incrementing the iterator returned by rbegin() past the end, yields an iterator equal to rend()")
+      {
+        auto it = ref.rbegin();
+        ++it;
+        ++it;
+        ++it;
+
+        REQUIRE(it == ref.rend());
+      }
     }
   }
 }