From 9ad0f9bb2bdfe47f144e2a0e8951dcfe6344a4ea Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 24 Aug 2024 16:58:01 -0400
Subject: Queue

---
 queue.go      | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 queue_test.go | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 queue.go
 create mode 100644 queue_test.go

diff --git a/queue.go b/queue.go
new file mode 100644
index 0000000..5e28412
--- /dev/null
+++ b/queue.go
@@ -0,0 +1,49 @@
+package share
+
+// Queue is a FIFO queue with an unlimited capacity.
+//
+// Closing the Enqueue channel closes the Queue. The Queue waits
+// until all elements have been drained from the Dequeue channel
+// before closing it.
+type Queue[T any] struct {
+	// Sending to Enqueue adds an element to the back of the Queue
+	// and never blocks.
+	Enqueue chan<-T
+
+
+	// Receiving from Dequeue removes an element from the front
+	// of the queue or, if the queue is empty, blocks until an element
+	// is enqueued.
+	Dequeue <-chan T
+}
+
+func NewQueue[T any]() Queue[T] {
+	in, out := make(chan T), make(chan T)
+
+	go func() {
+		defer close(out)
+
+		var queue []T
+
+		for v := range in {
+			queue = append(queue, v)
+
+			for len(queue) > 0 {
+				select {
+				case out <- queue[0]:
+					queue = queue[1:]
+				case v, ok := <-in:
+					if !ok {
+						for _, x := range queue {
+							out <- x
+						}
+						return
+					}
+					queue = append(queue, v)
+				}
+			}
+		}
+	}()
+
+	return Queue[T]{Enqueue: in, Dequeue: out}
+}
diff --git a/queue_test.go b/queue_test.go
new file mode 100644
index 0000000..33666d8
--- /dev/null
+++ b/queue_test.go
@@ -0,0 +1,37 @@
+package share_test
+
+import (
+	"testing"
+
+	"git.samanthony.xyz/share"
+)
+
+func TestQueue(t *testing.T) {
+	q := share.NewQueue[string]()
+
+	vals := []string{"foo", "bar", "baz", "xyz"}
+	
+	go func() {
+		for _, v := range vals {
+			q.Enqueue <- v
+		}
+		close(q.Enqueue)
+	}()
+
+	go func() {
+		i := 0
+		for front := range q.Dequeue {
+			t.Log("received", front, "from queue")
+			if i > len(vals)-1 {
+				t.Fatal("received too many elements from queue")
+			}
+			if front != vals[i] {
+				t.Fatalf("received %v from queue; wanted %v", front, vals[i])
+			}
+			i++
+		}
+		if i < len(vals) {
+			t.Fatal("did not receive enough values from queue")
+		}
+	}()
+}
\ No newline at end of file
-- 
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