implement RecordQueue type

internal/record.go

@@ -1,18 +1,56 @@
 package internal
 
 import (
+	"container/list"
 	"math/big"
 	"time"
 )
 
 type Record interface {
 	Symbol() string
+	Side() Side
 	Price() *big.Float
 	Quantity() *big.Float
-	Side() Side
 	Timestamp() time.Time
 }
 
-type RecordReader interface {
-	ReadRecord() (Record, error)
+type RecordQueue struct {
+	l *list.List
+}
+
+func (rq *RecordQueue) Push(r Record) {
+	if rq.l == nil {
+		rq.l = list.New()
+	}
+
+	if r == nil {
+		return
+	}
+
+	rq.l.PushBack(r)
+}
+
+// Pop removes and returns the first element of the list as the first return value. If the list is
+// empty returns falso on the 2nd return value, true otherwise.
+func (rq *RecordQueue) Pop() (Record, bool) {
+	if rq.l == nil {
+		return nil, false
+	}
+
+	el := rq.l.Front()
+	if el == nil {
+		return nil, false
+	}
+
+	val := rq.l.Remove(el)
+
+	return val.(Record), true
+}
+
+func (rq *RecordQueue) Len() int {
+	if rq.l == nil {
+		return 0
+	}
+
+	return rq.l.Len()
 }

internal/record_test.go

@@ -0,0 +1,59 @@
+package internal
+
+import (
+	"testing"
+)
+
+func TestRecordQueue_Push(t *testing.T) {
+	var recCount int
+	newRecord := func() Record {
+		recCount++
+		return testRecord{
+			id: recCount,
+		}
+	}
+
+	var rq RecordQueue
+	if rq.Len() != 0 {
+		t.Fatalf("zero value should have zero lenght")
+	}
+
+	_, ok := rq.Pop()
+	if ok {
+		t.Fatalf("Pop() should return (_,false) on a zero value")
+	}
+
+	rq.Push(nil)
+	if rq.Len() != 0 {
+		t.Fatalf("pushing nil should be a no-op")
+	}
+
+	rq.Push(newRecord())
+	if rq.Len() != 1 {
+		t.Fatalf("pushing 1st record should result in lenght of 1")
+	}
+
+	rq.Push(newRecord())
+	if rq.Len() != 2 {
+		t.Fatalf("pushing 2nd record should result in lenght of 2")
+	}
+
+	rec, 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.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")
+	}
+}
+
+type testRecord struct {
+	Record
+
+	id int
+}