//electValue chooses the best value for the variable in hand.
//The preferences goes as
// 1. The value read from the environment
// 2. The default value
// 3. Corresponding zero value if 1 & 2 fails and the variable
// is set as optional
//Returns error if the value is missing(both in environment
//and as default) and the variable is set to mandatory.
func (f *fieldMeta) electValue() (string, *models.EnvError) {
if f.valueHolder != "" {
return f.valueHolder, nil
} else if f.defVal != "" {
return f.defVal, nil
} else if f.mandatory {
return "", models.MandatoryValueMissing()
}
return "", models.OptionalValueMissing()
}
//Map performs the mapping of the environment value
//to the struct.
//source is the structure to which environment values
//are to be mapped.
func (e EnvToStruct) Map(source interface{}) error {
if source == nil {
return errors.New("ivalid source;")
}
rType := reflect.TypeOf(source)
if rType.Kind() != reflect.Ptr {
return errors.New("Expects pointer to target object")
}
rType = rType.Elem()
if rType.Kind() != reflect.Struct {
return errors.New("Expects pointer to struct")
}
rFieldNum := rType.NumField()
metaHolder := make(map[int]fieldMeta, rFieldNum)
for i := 0; i < rFieldNum; i++ {
rTFi := rType.Field(i)
thisMeta := fieldMeta{}
thisMeta.position = i
rFTag := rTFi.Tag.Get(APP_TAG)
tagInfo, tagEr := tagParser(rFTag)
if tagEr != nil {
return *tagEr
}
thisMeta.envName = tagInfo.name
thisMeta.mandatory = tagInfo.mandatory
thisMeta.defVal = tagInfo.deftVal
metaHolder[i] = thisMeta
}
metaHolder = e.envToHolder(e.appName+e.separator, metaHolder)
rValue := reflect.ValueOf(source)
if rValue.IsNil() {
return errors.New("pointer to nil obtained.")
}
if rValue.Kind() == reflect.Ptr {
rValue = rValue.Elem()
}
for i := 0; i < rFieldNum; i++ {
rVFi := rValue.Field(i)
rTFi := rType.Field(i)
if rVFi.Kind() == reflect.Ptr {
rVFi = rVFi.Elem()
}
if rVFi.CanSet() {
thisMeta := metaHolder[i]
electedVal, electionError := thisMeta.electValue()
if electionError != nil {
if *electionError == *models.OptionalValueMissing() {
continue
}
return *electionError.Field(rTFi.Name)
}
switch rTFi.Type.Kind() {
case reflect.Int:
intVal, convErr := strconv.Atoi(electedVal)
if convErr != nil {
return *models.InvalidValue().Field(rTFi.Name)
}
rVFi.Set(reflect.ValueOf(intVal))
case reflect.String:
rVFi.Set(reflect.ValueOf(electedVal))
}
}
}
return nil
}