Merge pull request 'Peek method for the RecordQueue type' (#3) from peeking-record-queue into main

Reviewed-on: applications/broker2anexoj#3

internal/record.go

@@ -38,14 +38,10 @@ func (rq *RecordQueue) Push(r Record) {
 	rq.l.PushBack(r)
 }
 
-// Pop removes and returns the first Record of the list as the first return value. If the list is
-// empty returns falso on the 2nd return value, true otherwise.
+// Pop removes and returns the first Record of the queue in the 1st return value. If the list is
+// empty returns false on the 2nd return value, true otherwise.
 func (rq *RecordQueue) Pop() (Record, bool) {
-	if rq == nil || rq.l == nil {
-		return nil, false
-	}
-
-	el := rq.l.Front()
+	el := rq.frontElement()
 	if el == nil {
 		return nil, false
 	}
@@ -55,6 +51,26 @@ func (rq *RecordQueue) Pop() (Record, bool) {
 	return val.(Record), true
 }
 
+// Peek returns the front Record of the queue in the 1st return value. If the list is empty returns
+// false on the 2nd return value, true otherwise.
+func (rq *RecordQueue) Peek() (Record, bool) {
+	el := rq.frontElement()
+	if el == nil {
+		return nil, false
+	}
+
+	return el.Value.(Record), true
+}
+
+func (rq *RecordQueue) frontElement() *list.Element {
+	if rq == nil || rq.l == nil {
+		return nil
+	}
+
+	return rq.l.Front()
+}
+
+// Len returns how many elements are currently on the queue
 func (rq *RecordQueue) Len() int {
 	if rq == nil || rq.l == nil {
 		return 0

internal/record_test.go

@@ -14,6 +14,7 @@ func TestRecordQueue(t *testing.T) {
 	}
 
 	var rq RecordQueue
+
 	if rq.Len() != 0 {
 		t.Fatalf("zero value should have zero lenght")
 	}
@@ -23,6 +24,11 @@ func TestRecordQueue(t *testing.T) {
 		t.Fatalf("Pop() should return (_,false) on a zero value")
 	}
 
+	_, ok = rq.Peek()
+	if ok {
+		t.Fatalf("Peek() should return (_,false) on a zero value")
+	}
+
 	rq.Push(nil)
 	if rq.Len() != 0 {
 		t.Fatalf("pushing nil should be a no-op")
@@ -38,18 +44,39 @@ func TestRecordQueue(t *testing.T) {
 		t.Fatalf("pushing 2nd record should result in lenght of 2")
 	}
 
-	rec, ok := rq.Pop()
+	peekRec, ok := rq.Peek()
+	if !ok {
+		t.Fatalf("Peek() should return (_,true) when the list is not empty")
+	}
+
+	if peekRec, ok := peekRec.(testRecord); ok {
+		if peekRec.id != 1 {
+			t.Fatalf("Peek() should return the 1st record pushed but returned %d", peekRec.id)
+		}
+	} else {
+		t.Fatalf("Peek() should return the original record type")
+	}
+
+	if rq.Len() != 2 {
+		t.Fatalf("Peek() should not affect the list length")
+	}
+
+	popRec, ok := rq.Pop()
 	if !ok {
 		t.Fatalf("Pop() should return (_,true) when the list is not empty")
 	}
 
-	if rec, ok := rec.(testRecord); ok {
+	if rec, ok := popRec.(testRecord); ok {
 		if rec.id != 1 {
 			t.Fatalf("Pop() should return the first record pushed but returned %d", rec.id)
 		}
 	} else {
 		t.Fatalf("Pop() should return the original record")
 	}
+
+	if rq.Len() != 1 {
+		t.Fatalf("Pop() should remove an element from the list")
+	}
 }
 
 func TestRecordQueueNilReceiver(t *testing.T) {
@@ -59,7 +86,12 @@ func TestRecordQueueNilReceiver(t *testing.T) {
 		t.Fatalf("nil receiver should have zero lenght")
 	}
 
-	_, ok := rq.Pop()
+	_, ok := rq.Peek()
+	if ok {
+		t.Fatalf("Peek() on a nil receiver should return (_,false)")
+	}
+
+	_, ok = rq.Pop()
 	if ok {
 		t.Fatalf("Pop() on a nil receiver should return (_,false)")
 	}