//
// Copyright 2023 Bytedance Ltd. and/or its affiliates
//
// 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 mysql

import (
	"reflect"
	"strings"
	"sync"
)

var schemaCache = &sync.Map{}

func hasValue(tag, attr string) bool {
	parts := strings.Split(tag, ";")
	for _, p := range parts {
		if strings.HasPrefix(strings.ToUpper(p), strings.ToUpper(attr)) {
			return true
		}
	}
	return false
}

func diffValue(a, b reflect.Value) (fields []string, diff bool) {
	a, b = reflect.Indirect(a), reflect.Indirect(b)
	if !a.IsValid() || !b.IsValid() {
		if a.IsValid() {
			b = reflect.New(a.Type()).Elem()
		} else if b.IsValid() {
			a = reflect.New(b.Type()).Elem()
		} else {
			diff = false
			return
		}
	}
	if a.IsZero() && b.IsZero() {
		diff = false
		return
	}
	switch {
	case a.Kind() == reflect.Struct:
		fields = diffStruct(a, b)
		diff = len(fields) > 0
	case a.Comparable() && b.Comparable():
		diff = !a.Equal(b)
	case a.CanInterface() && b.CanInterface():
		diff = !reflect.DeepEqual(a.Interface(), b.Interface())
	default:
		diff = true
	}
	return
}

func diffStruct(currVal, prevVal reflect.Value) []string {
	result := make([]string, 0)
	poType := currVal.Type()
	for i := 0; i < currVal.NumField(); i++ {
		field := poType.Field(i)
		fieldVal := currVal.Field(i)
		prevFiledVal := prevVal.Field(i)
		fieldVal, prevFiledVal = reflect.Indirect(fieldVal), reflect.Indirect(prevFiledVal)
		fieldName := field.Name
		fieldTag := field.Tag.Get("gorm")
		if fieldVal.Kind() == reflect.Struct {
			if structDiff, diff := diffValue(fieldVal, prevFiledVal); diff {
				if field.Anonymous || hasValue(fieldTag, "embedded") {
					result = append(result, structDiff...)
				} else {
					result = append(result, fieldName)
				}
			}
		} else {
			if _, diff := diffValue(fieldVal, prevFiledVal); diff {
				result = append(result, fieldName)
			}
		}
	}
	return result
}

// DiffModel 模型差异对比，返回gorm命名规范的更新数据
// 支持以下类型比对：常规数据类型(bool, int, float, string, time.Time)，嵌套可导出的非指针的 struct
func DiffModel(curr, prev interface{}) []string {
	currVal, prevVal := reflect.Indirect(reflect.ValueOf(curr)), reflect.Indirect(reflect.ValueOf(prev))
	if currVal.Kind() != reflect.Struct || prevVal.Kind() != reflect.Struct {
		return nil
	}
	return diffStruct(currVal, prevVal)
}