Add Incr function

Incr function added for increment integer values by one. pkg/main.go and README updated with  function usage.

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

README.md

@@ -81,6 +81,12 @@ func main() {
 	jack = db.Get("jack")
 	fmt.Println("Jack:", jack)
 
+	newAge, err := db.Incr("john")
+	if err != nil {
+		log.Fatalf(err.Error())
+	}
+	fmt.Printf("John's new age is %s", newAge)
+
 	err = db.Close() // Call while closing the database.
 	if err != nil {
 		log.Fatalf(err.Error())

example/pkg/main.go

@@ -27,6 +27,12 @@ func main() {
 	jack = db.Get("jack")
 	fmt.Println("Jack:", jack)
 
+	newAge, err := db.Incr("john")
+	if err != nil {
+		log.Fatalf(err.Error())
+	}
+	fmt.Printf("John's new age is %s", newAge)
+
 	err = db.Close()
 	if err != nil {
 		log.Fatalf(err.Error())

incr.go

@@ -0,0 +1,21 @@
+package kvs
+
+import "strconv"
+
+// Incr increments value of the key by 1. It is only applicable for integer
+// convertable values. If the value is not able to convert integer, it returns
+// error with empty string.
+func (k *Kvs) Incr(key string) (string, error) {
+	val := k.kv[key]
+	valInt, err := strconv.Atoi(val)
+	if err != nil {
+		return "", err
+	}
+	k.kv[key] = convStr(valInt + 1)
+	return k.kv[key], nil
+}
+
+// convStr converts integer to string.
+func convStr(i int) string {
+	return strconv.Itoa(i)
+}

incr_test.go

@@ -0,0 +1,81 @@
+package kvs
+
+import (
+	"os"
+	"testing"
+	"time"
+)
+
+func TestConvStr(t *testing.T) {
+	i := 12
+	s := convStr(i)
+	if s != "12" {
+		t.Fatalf("String conversion is wrong.")
+	}
+	t.Logf("Converted successfully: %s", s)
+}
+
+func TestKvs_Incr(t *testing.T) {
+	db, err := open(t.Name(), "", 2*time.Minute)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+	t.Logf("db created.")
+
+	k, v := "age", "12"
+	db.Set(k, v)
+	t.Logf("Key-value pair is set.")
+	t.Logf("%s: %s", k, v)
+	val, err := db.Incr(k)
+	if err != nil {
+		t.Fatalf(err.Error())
+	}
+
+	if val != "13" {
+		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_IncrStr(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.Incr(k)
+	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.")
+}