feat: new method--decrBy (#135)

structure/string.go

@@ -269,6 +269,34 @@ func (s *StringStructure) Decr(key []byte, ttl time.Duration) error {
 	return s.Set(key, newValue, ttl)
 }
 
+// DecrBy decrements the integer value of a key by the given amount
+// If the key does not exist, it will be created
+// If the key exists, it will be overwritten
+// If the key is expired, it will be deleted
+// If the key is not expired, it will be updated
+func (s *StringStructure) DecrBy(key []byte, amount int, ttl time.Duration) error {
+	// Get the old value
+	oldValue, err := s.Get(key)
+	if err != nil {
+		return err
+	}
+
+	// Convert the old value to an integer
+	oldIntValue, err := strconv.Atoi(string(oldValue))
+	if err != nil {
+		return err
+	}
+
+	// Decrement the integer value
+	newIntValue := oldIntValue - amount
+
+	// Convert the new integer value to a byte slice
+	newValue := []byte(strconv.Itoa(newIntValue))
+
+	// Set the value
+	return s.Set(key, newValue, ttl)
+}
+
 // encodeStringValue encodes the value
 // format: [type][expire][value]
 // type: 1 byte

structure/string_test.go

@@ -173,3 +173,20 @@ func TestStringStructure_Decr(t *testing.T) {
 	v2, _ := str.Get(randkv.GetTestKey(1))
 	assert.Equal(t, string(v2), "-1")
 }
+
+func TestStringStructure_DecrBy(t *testing.T) {
+	str := initdb()
+
+	err = str.Set(randkv.GetTestKey(1), []byte("1"), 0)
+	assert.Nil(t, err)
+
+	err := str.DecrBy(randkv.GetTestKey(1), 10, 0)
+	assert.Nil(t, err)
+	v1, _ := str.Get(randkv.GetTestKey(1))
+	assert.Equal(t, string(v1), "-9")
+
+	err = str.DecrBy(randkv.GetTestKey(1), 10, 0)
+	assert.Nil(t, err)
+	v2, _ := str.Get(randkv.GetTestKey(1))
+	assert.Equal(t, string(v2), "-19")
+}