1 files changed, 79 insertions, 0 deletions
diff --git a/internal/streamrow/ringbuffer.go b/internal/streamrow/ringbuffer.go
new file mode 100644
index 0000000..7820502
--- /dev/null
+++ b/internal/streamrow/ringbuffer.go
@@ -0,0 +1,79 @@
+package streamrow
+
+import "sync"
+
+const RingBufferCapacity = 10000
+
+// RingBuffer is a fixed-capacity circular buffer of stream rows used by the
+// tracing engine (write side) and the TUI stream view (read side). It
+// satisfies the runtime.EventSink interface (Push + Len + Snapshot).
+type RingBuffer struct {
+	mu          sync.RWMutex
+	buf         []Row
+	start       int
+	size        int
+	totalPushed uint64
+}
+
+// NewRingBuffer allocates an empty RingBuffer with the default capacity.
+func NewRingBuffer() *RingBuffer {
+	return &RingBuffer{buf: make([]Row, RingBufferCapacity)}
+}
+
+// Push appends a row to the ring buffer, overwriting the oldest entry when full.
+func (r *RingBuffer) Push(ev Row) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if r.size < RingBufferCapacity {
+		idx := (r.start + r.size) % RingBufferCapacity
+		r.buf[idx] = ev
+		r.size++
+	} else {
+		r.buf[r.start] = ev
+		r.start = (r.start + 1) % RingBufferCapacity
+	}
+	r.totalPushed++
+}
+
+// Snapshot returns a copy of all rows in insertion order.
+func (r *RingBuffer) Snapshot() []Row {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
+	if r.size == 0 {
+		return make([]Row, 0)
+	}
+
+	out := make([]Row, r.size)
+	for i := 0; i < r.size; i++ {
+		out[i] = r.buf[(r.start+i)%RingBufferCapacity]
+	}
+	return out
+}
+
+// Len returns the current number of rows in the buffer.
+func (r *RingBuffer) Len() int {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	return r.size
+}
+
+// TotalPushed returns the total number of rows pushed since construction or
+// the last Reset, including those that have been overwritten.
+func (r *RingBuffer) TotalPushed() uint64 {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	return r.totalPushed
+}
+
+// Reset clears all rows and resets the total-pushed counter.
+func (r *RingBuffer) Reset() {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	clear(r.buf)
+	r.start = 0
+	r.size = 0
+	r.totalPushed = 0
+}