Add DecrBy function

DecrementedBy feature added. Its tests and usage added. Also, missing comment line added in IncrBy

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

README.md

@@ -99,6 +99,12 @@ func main() {
 	}
 	fmt.Printf("John's decremented age is: %s\n", decrAge)
 
+	decrAge, err = db.DecrBy("john", 3)
+	if err != nil {
+		log.Fatalf(err.Error())
+	}
+	fmt.Printf("John's decremented age is: %s\n", decrAge)
+
 	exist := db.Exists("john")
 	fmt.Println(exist)
 

decr.go

@@ -17,3 +17,18 @@ func (k *Kvs) Decr(key string) (string, error) {
 	k.kv[key] = strconv.Itoa(valInt - 1)
 	return k.kv[key], nil
 }
+
+// DecrBy decreases the value by given value. If non-integer value is being
+// tried to decrement, it returns error.
+func (k *Kvs) DecrBy(key string, val int) (string, error) {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+
+	v := k.kv[key]
+	valInt, err := strconv.Atoi(v)
+	if err != nil {
+		return "", err
+	}
+	k.kv[key] = strconv.Itoa(valInt - val)
+	return k.kv[key], nil
+}

decr_test.go

@@ -70,3 +70,68 @@ func TestKvs_DecrStr(t *testing.T) {
 	}
 	t.Logf("temp db removed.")
 }
+
+func TestKvs_DecrBy(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.DecrBy(k, i)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+
+	if val != "9" {
+		t.Errorf("decremented value is wrong: %s", val)
+	}
+	t.Logf("value is decremented.")
+	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_DecrByStr(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.DecrBy(k, 3)
+	if err == nil {
+		t.Fatalf("error expected, but nil got.")
+	}
+	t.Logf("value could not decremented. 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.")
+}

example/pkg/main.go

@@ -45,6 +45,12 @@ func main() {
 	}
 	fmt.Printf("John's decremented age is: %s\n", decrAge)
 
+	decrAge, err = db.DecrBy("john", 3)
+	if err != nil {
+		log.Fatalf(err.Error())
+	}
+	fmt.Printf("John's decremented age is: %s\n", decrAge)
+
 	exist := db.Exists("john")
 	fmt.Println(exist)
 

incr.go

@@ -16,7 +16,7 @@ func (k *Kvs) Incr(key string) (string, error) {
 }
 
 // IncrBy increments the value by given value. If non-integer value is being
-// tried to increment,
+// tried to increment, it returns error.
 func (k *Kvs) IncrBy(key string, val int) (string, error) {
 	v := k.kv[key]
 	valInt, err := strconv.Atoi(v)