proptools/proptools.go

// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// 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 proptools

import (
	"fmt"
	"reflect"
	"strings"
	"unicode"
	"unicode/utf8"
)

func PropertyNameForField(fieldName string) string {
	r, size := utf8.DecodeRuneInString(fieldName)
	propertyName := string(unicode.ToLower(r))
	if len(fieldName) > size {
		propertyName += fieldName[size:]
	}
	return propertyName
}

func FieldNameForProperty(propertyName string) string {
	r, size := utf8.DecodeRuneInString(propertyName)
	fieldName := string(unicode.ToUpper(r))
	if len(propertyName) > size {
		fieldName += propertyName[size:]
	}
	return fieldName
}

func CloneProperties(structValue reflect.Value) reflect.Value {
	result := reflect.New(structValue.Type())
	CopyProperties(result.Elem(), structValue)
	return result
}

func CopyProperties(dstValue, srcValue reflect.Value) {
	typ := dstValue.Type()
	if srcValue.Type() != typ {
		panic(fmt.Errorf("can't copy mismatching types (%s <- %s)",
			dstValue.Kind(), srcValue.Kind()))
	}

	for i := 0; i < srcValue.NumField(); i++ {
		field := typ.Field(i)
		if field.PkgPath != "" {
			// The field is not exported so just skip it.
			continue
		}

		srcFieldValue := srcValue.Field(i)
		dstFieldValue := dstValue.Field(i)

		switch srcFieldValue.Kind() {
		case reflect.Bool, reflect.String, reflect.Int, reflect.Uint:
			dstFieldValue.Set(srcFieldValue)
		case reflect.Struct:
			CopyProperties(dstFieldValue, srcFieldValue)
		case reflect.Slice:
			if !srcFieldValue.IsNil() {
				if field.Type.Elem().Kind() != reflect.String {
					panic(fmt.Errorf("can't copy field %q: slice elements are "+
						"not strings", field.Name))
				}
				if srcFieldValue != dstFieldValue {
					newSlice := reflect.MakeSlice(field.Type, srcFieldValue.Len(),
						srcFieldValue.Len())
					reflect.Copy(newSlice, srcFieldValue)
					dstFieldValue.Set(newSlice)
				}
			} else {
				dstFieldValue.Set(srcFieldValue)
			}
		case reflect.Ptr, reflect.Interface:
			if !srcFieldValue.IsNil() {
				if dstFieldValue.IsNil() ||
					dstFieldValue.Type() != srcFieldValue.Type() {

					// We can't use the existing destination allocation, so
					// clone a new one.
					elem := srcFieldValue.Elem()
					if srcFieldValue.Kind() == reflect.Interface {
						if elem.Kind() != reflect.Ptr {
							panic(fmt.Errorf("can't clone field %q: interface "+
								"refers to a non-pointer", field.Name))
						}
						elem = elem.Elem()
					}
					if elem.Kind() != reflect.Struct {
						panic(fmt.Errorf("can't clone field %q: points to a "+
							"non-struct", field.Name))
					}
					dstFieldValue.Set(CloneProperties(elem))
				} else {
					// Re-use the existing allocation.
					CopyProperties(dstFieldValue.Elem().Elem(), srcFieldValue.Elem().Elem())
				}
			} else {
				dstFieldValue.Set(srcFieldValue)
			}
		default:
			panic(fmt.Errorf("unexpected kind for property struct field %q: %s",
				field.Name, srcFieldValue.Kind()))
		}
	}
}

func ZeroProperties(structValue reflect.Value) {
	typ := structValue.Type()

	for i := 0; i < structValue.NumField(); i++ {
		field := typ.Field(i)
		if field.PkgPath != "" {
			// The field is not exported so just skip it.
			continue
		}

		fieldValue := structValue.Field(i)

		switch fieldValue.Kind() {
		case reflect.Bool, reflect.String, reflect.Struct, reflect.Slice, reflect.Int, reflect.Uint:
			fieldValue.Set(reflect.Zero(fieldValue.Type()))
		case reflect.Ptr, reflect.Interface:
			if !fieldValue.IsNil() {
				// We leave the pointer intact and zero out the struct that's
				// pointed to.
				elem := fieldValue.Elem()
				if fieldValue.Kind() == reflect.Interface {
					if elem.Kind() != reflect.Ptr {
						panic(fmt.Errorf("can't zero field %q: interface "+
							"refers to a non-pointer", field.Name))
					}
					elem = elem.Elem()
				}
				if elem.Kind() != reflect.Struct {
					panic(fmt.Errorf("can't zero field %q: points to a "+
						"non-struct", field.Name))
				}
				ZeroProperties(elem)
			}
		default:
			panic(fmt.Errorf("unexpected kind for property struct field %q: %s",
				field.Name, fieldValue.Kind()))
		}
	}
}

func CloneEmptyProperties(structValue reflect.Value) reflect.Value {
	result := reflect.New(structValue.Type())
	cloneEmptyProperties(result.Elem(), structValue)
	return result
}

func cloneEmptyProperties(dstValue, srcValue reflect.Value) {
	typ := srcValue.Type()
	for i := 0; i < srcValue.NumField(); i++ {
		field := typ.Field(i)
		if field.PkgPath != "" {
			// The field is not exported so just skip it.
			continue
		}

		srcFieldValue := srcValue.Field(i)
		dstFieldValue := dstValue.Field(i)

		switch srcFieldValue.Kind() {
		case reflect.Bool, reflect.String, reflect.Slice, reflect.Int, reflect.Uint:
			// Nothing
		case reflect.Struct:
			cloneEmptyProperties(dstFieldValue, srcFieldValue)
		case reflect.Ptr, reflect.Interface:
			if !srcFieldValue.IsNil() {
				elem := srcFieldValue.Elem()
				if srcFieldValue.Kind() == reflect.Interface {
					if elem.Kind() != reflect.Ptr {
						panic(fmt.Errorf("can't clone field %q: interface "+
							"refers to a non-pointer", field.Name))
					}
					elem = elem.Elem()
				}
				if elem.Elem().Kind() != reflect.Struct {
					panic(fmt.Errorf("can't clone field %q: points to a "+
						"non-struct", field.Name))
				}
				dstFieldValue.Set(CloneEmptyProperties(elem.Elem()))
			}
		default:
			panic(fmt.Errorf("unexpected kind for property struct field %q: %s",
				field.Name, srcFieldValue.Kind()))
		}
	}
}

func HasTag(field reflect.StructField, name, value string) bool {
	tag := field.Tag.Get(name)
	for _, entry := range strings.Split(tag, ",") {
		if entry == value {
			return true
		}
	}

	return false
}