fillin.go

/*
Copyright 2020 The Magma Authors.

This source code is licensed under the BSD-style license found in the
LICENSE file in the root directory of this source tree.

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package mconfig is protoc generated GRPC package as well as helper functions such as FillIn
package protos

import (
	"reflect"
	"strings"
)

// Go Struct tag to specify an alternative name for field name matching
const MAGMA_ALT_NAME_TAG string = "magma_alt_name"

//
// FillIn assigns matching field values of src to dest
// A fields from src & dest are considered "matching" if they have
// identical names & Types
// FillIn will recursively inspect structures to find matching fields
// and return number of successfully set fields
func FillIn(src interface{}, dest interface{}) int {
	if src == nil || dest == nil {
		return 0 // nothing to do
	}
	vs, vd := reflect.ValueOf(src), reflect.ValueOf(dest)
	return fillIn(&vs, &vd)
}

func fillIn(vs *reflect.Value, vd *reflect.Value) int {

	var savedVd *reflect.Value

	ks, kd := vs.Kind(), vd.Kind()
	// First, "dereference" pointers and corresponding parameters
	for ks == reflect.Ptr && kd == reflect.Ptr {
		if vs.IsNil() { // nothing coming from source, return
			return 0
		}
		var vdo reflect.Value
		if vd.IsNil() { // check if we need initialize destination
			if !vd.CanSet() { // dest is not settable, return
				return 0
			}
			savedVd = vd
			vdo = reflect.New(vd.Type().Elem()).Elem()
			vd = &vdo
		} else {
			vdo = vd.Elem()
		}

		vso := vs.Elem()
		vs, vd = &vso, &vdo
		ks, kd = vs.Kind(), vd.Kind()
		if ks != kd && !vs.Type().ConvertibleTo(vd.Type()) {
			return 0
		}
	}

	if !vd.CanSet() {
		return 0 // dest is not settable after differencing - nothing to do
	}

	ts, td := vs.Type(), vd.Type()
	if ts.AssignableTo(td) { // value types match, we can assign directly
		vd.Set(*vs)
	} else if ts.ConvertibleTo(td) { // value types are compatible - assign
		vd.Set(vs.Convert(td))
	} else { // if it's a struct, iterate over all public fields
		count := 0 // keep count of total set fields recursively
		if ks == reflect.Struct && kd == reflect.Struct {
			count = convertStruct(vs, vd)
		}
		if ks == reflect.Map && kd == reflect.Map {
			count = convertMap(vs, vd)
		}
		// if no matching fields (count == 0), leave nil Ptr at nil
		if savedVd != nil && count > 0 {
			savedVd.Set(vd.Addr())
		}
		return count
	}

	// value was set directly, update nil Ptr if needed
	if savedVd != nil {
		savedVd.Set(vd.Addr())
	}
	return 1
}

func convertStruct(vs *reflect.Value, vd *reflect.Value) int {
	count := 0
	altSrcNames := map[string]int{}
	ts, td := vs.Type(), vd.Type()
	for i := 0; i < ts.NumField(); i++ {
		fts := ts.Field(i)
		if altNm := fts.Tag.Get(MAGMA_ALT_NAME_TAG); len(altNm) > 0 {
			altSrcNames[altNm] = i
		}
	}
	for i := 0; i < td.NumField(); i++ {
		ftd := td.Field(i)
		fs := vs.FieldByName(ftd.Name)
		if !fs.IsValid() {
			if altNm := ftd.Tag.Get(MAGMA_ALT_NAME_TAG); len(altNm) > 0 {
				fs = vs.FieldByName(altNm)
			}
			if !fs.IsValid() {
				sidx, ok := altSrcNames[ftd.Name]
				if ok {
					fs = vs.Field(sidx)
				} else {
					fsnl := ftd.Name[:1] + strings.ToLower(ftd.Name[1:]) // to lower case, but preserve the first rune
					fs = vs.FieldByNameFunc(func(sn string) bool { return sn[:1]+strings.ToLower(sn[1:]) == fsnl })
					if !fs.IsValid() {
						continue
					}
				}
			}
		}
		vdf := vd.Field(i)
		if fs.Kind() == vdf.Kind() || fs.Type().ConvertibleTo(ftd.Type) {
			count += fillIn(&fs, &vdf)
		}
	}
	return count
}

func convertMap(vs *reflect.Value, vd *reflect.Value) int {
	count := 0
	if len(vs.MapKeys()) > 0 {
		vd.Set(reflect.MakeMap(vd.Type()))
	}
	for _, mapKey := range vs.MapKeys() {
		mapVal := vs.MapIndex(mapKey)
		if mapVal.Kind() == reflect.Ptr {
			if mapVal.IsNil() {
				continue
			}
			mapVal = mapVal.Elem()
		}
		copyVal := reflect.New(vd.Type().Elem()).Elem()
		if copyVal.Kind() == reflect.Ptr {
			copyValObj := reflect.New(copyVal.Type().Elem()).Elem()
			fillIn(&mapVal, &copyValObj)
			copyVal.Set(copyValObj.Addr())
		} else {
			fillIn(&mapVal, &copyVal)
		}
		vd.SetMapIndex(mapKey, copyVal)
	}
	return count
}

// SafeInit traverses given struct ptr and fills in all nil struct pointer, map & slice fields with defult initialized
// elements recursively
func SafeInit(s interface{}) interface{} {
	t := reflect.TypeOf(s)
	k := t.Kind()
	v := reflect.ValueOf(s)

	if s == nil || ((k == reflect.Ptr || k == reflect.Slice || k == reflect.Map) && v.IsNil()) {
		switch k {
		case reflect.Ptr:
			s = reflect.New(t.Elem()).Interface()
		case reflect.Slice:
			s = reflect.MakeSlice(t, 0, 0).Interface()
		case reflect.Map:
			s = reflect.MakeMap(t).Interface()
		}
		t = reflect.TypeOf(s)
		k = t.Kind()
		v = reflect.ValueOf(s)
	}
	if k == reflect.Ptr {
		t = t.Elem()
		if t.Kind() == reflect.Struct {
			v = v.Elem()
			fn := t.NumField()
			for i := 0; i < fn; i++ {
				switch t.Field(i).Type.Kind() {
				case reflect.Ptr, reflect.Map, reflect.Slice:
					fv := v.Field(i)
					newFld := SafeInit(fv.Interface())
					if fv.IsNil() && fv.CanSet() {
						fv.Set(reflect.ValueOf(newFld))
					}
				case reflect.Struct:
					fv := v.Field(i)
					if fv.CanAddr() {
						SafeInit(fv.Addr().Interface())
					}
				}
			}
		}
	}
	return s
}