object.go

package stringreplace

import (
	"reflect"

	"github.com/golang/glog"
)

// VisitObjectStrings visits recursively all string fields in the object and call the
// visitor function on them. The visitor function can be used to modify the
// value of the string fields.
func VisitObjectStrings(obj interface{}, visitor func(string) string) {
	visitValue(reflect.ValueOf(obj), visitor)
}

func visitValue(v reflect.Value, visitor func(string) string) {
	// you'll never be able to substitute on a nil.  Check the kind first or you'll accidentally
	// end up panic-ing
	switch v.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
		if v.IsNil() {
			return
		}
	}

	switch v.Kind() {

	case reflect.Ptr:
		visitValue(v.Elem(), visitor)
	case reflect.Interface:
		visitValue(reflect.ValueOf(v.Interface()), visitor)

	case reflect.Slice, reflect.Array:
		vt := v.Type().Elem()
		for i := 0; i < v.Len(); i++ {
			val := visitUnsettableValues(vt, v.Index(i), visitor)
			v.Index(i).Set(val)
		}
	case reflect.Struct:
		for i := 0; i < v.NumField(); i++ {
			visitValue(v.Field(i), visitor)
		}

	case reflect.Map:
		vt := v.Type().Elem()
		for _, k := range v.MapKeys() {
			val := visitUnsettableValues(vt, v.MapIndex(k), visitor)
			v.SetMapIndex(k, val)
		}

	case reflect.String:
		if !v.CanSet() {
			glog.Infof("Unable to set String value '%v'", v)
			return
		}
		v.SetString(visitor(v.String()))

	default:
		glog.V(5).Infof("Unknown field type '%s': %v", v.Kind(), v)
	}
}

// visitUnsettableValues creates a copy of the object you want to modify and returns the modified result
func visitUnsettableValues(typeOf reflect.Type, original reflect.Value, visitor func(string) string) reflect.Value {
	val := reflect.New(typeOf).Elem()
	existing := original
	// if the value type is interface, we must resolve it to a concrete value prior to setting it back.
	if existing.CanInterface() {
		existing = reflect.ValueOf(existing.Interface())
	}
	switch existing.Kind() {
	case reflect.String:
		s := visitor(existing.String())
		val.Set(reflect.ValueOf(s))
	default:
		if existing.IsValid() && existing.Kind() != reflect.Invalid {
			val.Set(existing)
		}
		visitValue(val, visitor)
	}

	return val
}