Add IncrBy function

IncrBy function added as a new feature. Example code added to pkg/main.go and README.

Signed-off-by: Gökhan Özeloğlu <gozeloglu@gmail.com>

README.md

@@ -87,6 +87,12 @@ func main() {
 	}
 	fmt.Printf("John's new age is %s", newAge)
 
+	newAge, err = db.IncrBy("john", 3)
+	if err != nil {
+		log.Fatalf(err.Error())
+	}
+	fmt.Printf("John's new age is %s\n", newAge)
+
 	err = db.Close() // Call while closing the database.
 	if err != nil {
 		log.Fatalf(err.Error())

example/pkg/main.go

@@ -31,7 +31,13 @@ func main() {
 	if err != nil {
 		log.Fatalf(err.Error())
 	}
-	fmt.Printf("John's new age is %s", newAge)
+	fmt.Printf("John's new age is %s\n", newAge)
+
+	newAge, err = db.IncrBy("john", 3)
+	if err != nil {
+		log.Fatalf(err.Error())
+	}
+	fmt.Printf("John's new age is %s\n", newAge)
 
 	err = db.Close()
 	if err != nil {

incr.go

@@ -15,6 +15,18 @@ func (k *Kvs) Incr(key string) (string, error) {
 	return k.kv[key], nil
 }
 
+// IncrBy increments the value by given value. If non-integer value is being
+// tried to increment,
+func (k *Kvs) IncrBy(key string, val int) (string, error) {
+	v := k.kv[key]
+	valInt, err := strconv.Atoi(v)
+	if err != nil {
+		return "", err
+	}
+	k.kv[key] = convStr(valInt + val)
+	return k.kv[key], err
+}
+
 // convStr converts integer to string.
 func convStr(i int) string {
 	return strconv.Itoa(i)

incr_test.go

@@ -79,3 +79,68 @@ func TestKvs_IncrStr(t *testing.T) {
 	}
 	t.Logf("temp db removed.")
 }
+
+func TestKvs_IncrBy(t *testing.T) {
+	db, err := open(t.Name(), "", 2*time.Minute)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("db created.")
+
+	k, v, i := "age", "12", 3
+	db.Set(k, v)
+	t.Logf("Key-value pair is set.")
+	t.Logf("%s: %s", k, v)
+	val, err := db.IncrBy(k, i)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+
+	if val != "15" {
+		t.Errorf("incremented value is wrong: %s", val)
+	}
+	t.Logf("value is incremented.")
+	t.Logf("%s: %s", k, val)
+
+	err = db.Close()
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("db closed.")
+
+	err = os.RemoveAll(db.dir)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("temp db removed.")
+}
+
+func TestKvs_IncrByStr(t *testing.T) {
+	db, err := open(t.Name(), "", 2*time.Minute)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("db created.")
+
+	k, v := "foo", "bar"
+	db.Set(k, v)
+	t.Logf("Key-value pair is set.")
+	t.Logf("%s: %s", k, v)
+	_, err = db.IncrBy(k, 3)
+	if err == nil {
+		t.Fatalf("error expected, but nil got.")
+	}
+	t.Logf("value could not incremented. it is string.")
+
+	err = db.Close()
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("db closed.")
+
+	err = os.RemoveAll(db.dir)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("temp db removed.")
+}