Adds clear method and test for CircularBuffer (#176)

* added clear method and test

* removed some duplicate code from the constructor and call new clear method

* changes based on PR comments

* fixed build issue

src/Featurizers/Components/UnitTests/WindowFeaturizerBase_UnitTest.cpp

@@ -408,3 +408,49 @@ TEST_CASE("CircularBuffer - range with offset") {
     // when n and offset are not out of bound
     CHECK(++(++start_iter3) == end_iter3);
 }
+
+TEST_CASE("CircularBuffer - clear") {
+    NS::Featurizers::Components::CircularBuffer<std::int16_t> circ_buf(5);
+    
+    // Add some dummy data
+    circ_buf.push(1);
+    circ_buf.push(2);
+    CHECK(circ_buf.size() == 2);
+
+    // Make sure after clear the size is correct
+    circ_buf.clear();
+    CHECK(circ_buf.size() == 0);
+
+    // Make sure start/end iters are correct after clear
+    auto start_iter = circ_buf.begin();
+    auto end_iter = circ_buf.end();
+    CHECK(start_iter == end_iter);
+    CHECK(circ_buf.capacity() == 5);
+
+    // Add one item and make sure start offset is correct.
+    circ_buf.push(1);
+    auto start_iter2 = circ_buf.begin();
+    CHECK(*start_iter2 == 1);
+
+    // Add till the size is full and make sure capacity is still the same.
+    circ_buf.push(2);
+    circ_buf.push(3);
+    circ_buf.push(4);
+    circ_buf.push(5);
+    circ_buf.push(6);
+    CHECK(circ_buf.size() == 5);
+
+    // Make sure size is correct after final clear.
+    circ_buf.clear();
+    CHECK(circ_buf.size() == 0);
+
+    // Make sure start/end iters are correct after clear
+    auto start_iter3 = circ_buf.begin();
+    auto end_iter3 = circ_buf.end();
+    CHECK(start_iter3 == end_iter3);
+
+    // One more time add one item and make sure the start offset is correct.
+    circ_buf.push(1);
+    auto start_iter4 = circ_buf.begin();
+    CHECK(*start_iter4 == 1);
+}

src/Featurizers/Components/WindowFeaturizerBase.h

@@ -135,6 +135,8 @@ namespace Components {
         // ----------------------------------------------------------------------
         CircularBuffer(size_t max_size);
 
+        void clear();
+
         size_t size() const;
 
         size_t capacity() const;
@@ -291,11 +293,23 @@ bool CircularIterator<T>::at_end() const {
 // ----------------------------------------------------------------------
 
 template <class T>
-CircularBuffer<T>::CircularBuffer(size_t max_size) : _max_size(max_size), _start_offset(0) {
+CircularBuffer<T>::CircularBuffer(size_t max_size) : _max_size(max_size) {
     if (_max_size == 0) {
         throw std::invalid_argument("Max size cannot be zero");
     }
 
+    clear();
+}
+
+template <class T>
+void CircularBuffer<T>::clear() {
+    _data.clear();
+
+    // Make sure that the start offset is back to 0;
+    _start_offset = 0;
+    
+    // The c++ reference says "the vector capacity is not guaranteed to change due to calling this function."
+    // Since the capacity may change, calling reserve again just to make sure we still have the correct size.
     _data.reserve(_max_size);
 }
 
@@ -306,7 +320,7 @@ size_t CircularBuffer<T>::size() const {
 
 template <class T>
 size_t CircularBuffer<T>::capacity() const {
-    return _max_size;
+    return _data.capacity();
 }
 
 template <class T>