add GetMessageType

Makefile

@@ -0,0 +1,4 @@
+test:
+	@go test
+
+.PHONY: test

list_test.go

@@ -1,19 +1,11 @@
 package midi
 
 import (
-	"fmt"
 	"testing"
 )
 
 func TestDevices(t *testing.T) {
-	devices, err := Devices()
-	if err != nil {
+	if _, err := Devices(); err != nil {
 		t.Fatal(err)
 	}
-	for i, d := range devices {
-		if d == nil {
-			continue
-		}
-		fmt.Printf("device %d: %#v\n", i, *d)
-	}
 }

midi.go

@@ -28,3 +28,23 @@ type CC struct {
 	Number int
 	Value  int
 }
+
+const (
+	MessageTypeUnknown = iota
+	MessageTypeCC
+	MessageTypeNoteOff
+	MessageTypeNoteOn
+	MessageTypePolyKeyPressure
+)
+
+// GetMessageType returns the message type for the provided packet.
+func GetMessageType(p Packet) int {
+	switch p.Data[0] & 0xF0 {
+	case 0x80:
+		return MessageTypeNoteOff
+	case 0x90:
+		return MessageTypeNoteOn
+	default:
+		return MessageTypeUnknown
+	}
+}

midi_test.go

@@ -0,0 +1,28 @@
+package midi
+
+import (
+	"testing"
+)
+
+func TestGetMessageType(t *testing.T) {
+	for _, tc := range []struct {
+		Expect int
+		Input  Packet
+		Name   string
+	}{
+		{
+			Expect: MessageTypeNoteOn,
+			Input:  Packet{Data: [3]uint8{0x90, 0x4f, 0x16}},
+			Name:   "Note On message type",
+		},
+		{
+			Expect: MessageTypeNoteOff,
+			Input:  Packet{Data: [3]uint8{0x80, 0x4f, 0x0}},
+			Name:   "Note Off message type",
+		},
+	} {
+		if expect, got := tc.Expect, GetMessageType(tc.Input); expect != got {
+			t.Fatalf("%s: expected %d, got %d", tc.Name, expect, got)
+		}
+	}
+}