almost done, queue fix next

util/queue/structs.go

@@ -0,0 +1,66 @@
+package queue
+
+import (
+	"sync"
+)
+
+// Queue is a thin wrapper around a buffered channel.
+type Queue[T any] struct {
+	ch       chan T
+	closedMu sync.Mutex
+	closed   bool
+	closedCh chan struct{}
+}
+
+func NewQueue[T any](capacity int) *Queue[T] {
+	if capacity <= 0 {
+		panic("capacity > 0 required")
+	}
+
+	return &Queue[T]{
+		ch:       make(chan T, capacity),
+		closedCh: make(chan struct{}),
+	}
+}
+
+// Cap returns capacity.
+func (q *Queue[T]) Cap() int { return cap(q.ch) }
+
+// Len returns current length (snapshot).
+func (q *Queue[T]) Len() int { return len(q.ch) }
+
+// Enqueue returns immediately: true if enqueued, false otherwise.
+func (q *Queue[T]) Enqueue(v T) bool {
+	select {
+	case q.ch <- v:
+		return true
+	default:
+		return false
+	}
+}
+
+// Dequeue returns immediately (item, true) or (zero, false) if empty.
+func (q *Queue[T]) Dequeue() (T, bool) {
+	var zero T
+	select {
+	case v := <-q.ch:
+		return v, true
+	default:
+		return zero, false
+	}
+}
+
+// Close closes the queue. Further Enqueue attempts return ErrClosed. Consumers drain until channel empty then see ErrClosed.
+func (q *Queue[T]) Close() {
+	q.closedMu.Lock()
+
+	if q.closed {
+		q.closedMu.Unlock()
+		return
+	}
+
+	q.closed = true
+	close(q.closedCh)
+	close(q.ch)
+	q.closedMu.Unlock()
+}