new filler abstraction

Author: mcuadros

filler.go

@@ -0,0 +1,109 @@
+package defaults
+
+import (
+	"reflect"
+)
+
+type fieldData struct {
+	Field reflect.StructField
+	Value reflect.Value
+}
+
+type fillerFunc func(field *fieldData, config string)
+
+type Filler struct {
+	FuncByName map[string]fillerFunc
+	FuncByKind map[reflect.Kind]fillerFunc
+	Tag        string
+}
+
+func (self *Filler) Fill(variable interface{}) {
+	fields := self.getFields(variable)
+	self.setDefaultValues(fields)
+}
+
+func (self *Filler) getFields(variable interface{}) []*fieldData {
+	valueObject := reflect.ValueOf(variable).Elem()
+
+	return self.getFieldsFromValue(valueObject)
+}
+
+func (self *Filler) getFieldsFromValue(valueObject reflect.Value) []*fieldData {
+	typeObject := valueObject.Type()
+
+	count := valueObject.NumField()
+	results := make([]*fieldData, 0)
+	for i := 0; i < count; i++ {
+		value := valueObject.Field(i)
+		field := typeObject.Field(i)
+
+		if value.CanSet() {
+			results = append(results, &fieldData{
+				Value: value,
+				Field: field,
+			})
+		}
+	}
+
+	return results
+}
+
+func (self *Filler) setDefaultValues(fields []*fieldData) {
+	for _, field := range fields {
+		if self.isEmpty(field) {
+			self.setDefaultValue(field)
+		}
+	}
+}
+
+func (self *Filler) isEmpty(field *fieldData) bool {
+	switch field.Value.Kind() {
+	case reflect.Bool:
+		if field.Value.Bool() != false {
+			return false
+		}
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		if field.Value.Int() != 0 {
+			return false
+		}
+	case reflect.Float32, reflect.Float64:
+		if field.Value.Float() != .0 {
+			return false
+		}
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		if field.Value.Uint() != 0 {
+			return false
+		}
+	case reflect.Slice:
+		if field.Value.Type().Elem().Kind() == reflect.Uint8 {
+			if field.Value.Bytes() != nil {
+				return false
+			}
+		}
+	case reflect.String:
+		if field.Value.String() != "" {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (self *Filler) setDefaultValue(field *fieldData) {
+	tagValue := field.Field.Tag.Get(self.Tag)
+
+	function := self.getFunctionByKind(field.Field.Type.Kind())
+	if function == nil {
+		return
+	}
+
+	function(field, tagValue)
+}
+
+func (self *Filler) getFunctionByKind(k reflect.Kind) fillerFunc {
+	if f, ok := self.FuncByKind[k]; ok == true {
+		return f
+	}
+
+	return nil
+}