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/*
 * Copyright 2020-2022 the original author or authors.
 *
 * 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 io.mybatis.provider.defaults;

import io.mybatis.provider.EntityClassFinder;

import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.Optional;

/**
 * 根据泛型，从返回值、参数、接口泛型参数来判断对应的实体类类型
 *
 * @author liuzh
 */
public abstract class GenericEntityClassFinder implements EntityClassFinder {

  @Override
  public Optional> findEntityClass(Class mapperType, Method mapperMethod) {
    //先判断返回值
    Optional> optionalClass;
    if (mapperMethod != null) {
      optionalClass = getEntityClassByMapperMethodReturnType(mapperType, mapperMethod);
      if (optionalClass.isPresent()) {
        return optionalClass;
      }
      //再判断参数
      optionalClass = getEntityClassByMapperMethodParamTypes(mapperType, mapperMethod);
      if (optionalClass.isPresent()) {
        return optionalClass;
      }
      //最后从接口泛型中获取
      optionalClass = getEntityClassByMapperMethodAndMapperType(mapperType, mapperMethod);
      if (optionalClass.isPresent()) {
        return optionalClass;
      }
    }
    return getEntityClassByMapperType(mapperType);
  }

  /**
   * 根据方法返回值获取
   *
   * @param mapperType   接口
   * @param mapperMethod 方法
   * @return 实体类类型
   */
  protected Optional> getEntityClassByMapperMethodReturnType(Class mapperType, Method mapperMethod) {
    Class returnType = GenericTypeResolver.getReturnType(mapperMethod, mapperType);
    return isEntityClass(returnType) ? Optional.of(returnType) : Optional.empty();
  }

  /**
   * 根据方法参数获取
   *
   * @param mapperType   接口
   * @param mapperMethod 方法
   * @return 实体类类型
   */
  protected Optional> getEntityClassByMapperMethodParamTypes(Class mapperType, Method mapperMethod) {
    return getEntityClassByTypes(GenericTypeResolver.resolveParamTypes(mapperMethod, mapperType));
  }

  /**
   * 根据方法所在接口泛型获取，只有定义在泛型接口中的方法才能通过泛型获取，定义的最终使用类中的无法通过泛型获取
   *
   * @param mapperType   接口
   * @param mapperMethod 方法
   * @return 实体类类型
   */
  protected Optional> getEntityClassByMapperMethodAndMapperType(Class mapperType, Method mapperMethod) {
    return getEntityClassByTypes(GenericTypeResolver.resolveMapperTypes(mapperMethod, mapperType));
  }

  /**
   * 根据接口泛型获取，当前方法只根据接口泛型获取实体类，和当前执行的方法无关，是优先级最低的一种情况
   *
   * @param mapperType 接口
   * @return 实体类类型
   */
  protected Optional> getEntityClassByMapperType(Class mapperType) {
    return getEntityClassByTypes(GenericTypeResolver.resolveMapperTypes(mapperType));
  }

  /**
   * 根据 type 获取可能的实体类型
   *
   * @param type 类型
   * @return 实体类类型
   */
  protected Optional> getEntityClassByType(Type type) {
    if (type instanceof Class) {
      if (isEntityClass((Class) type)) {
        return Optional.of((Class) type);
      }
    } else if (type instanceof GenericTypeResolver.ParameterizedTypeImpl) {
      return getEntityClassByTypes(((GenericTypeResolver.ParameterizedTypeImpl) type).getActualTypeArguments());
    } else if (type instanceof GenericTypeResolver.WildcardTypeImpl) {
      Optional> optionalClass = getEntityClassByTypes(((GenericTypeResolver.WildcardTypeImpl) type).getLowerBounds());
      if (optionalClass.isPresent()) {
        return optionalClass;
      }
      return getEntityClassByTypes(((GenericTypeResolver.WildcardTypeImpl) type).getUpperBounds());
    } else if (type instanceof GenericTypeResolver.GenericArrayTypeImpl) {
      return getEntityClassByType(((GenericTypeResolver.GenericArrayTypeImpl) type).getGenericComponentType());
    }
    return Optional.empty();
  }

  /**
   * 遍历 types 获取可能的实体类型
   *
   * @param types 类型
   * @return 实体类类型
   */
  protected Optional> getEntityClassByTypes(Type[] types) {
    for (Type type : types) {
      Optional> optionalClass = getEntityClassByType(type);
      if (optionalClass.isPresent()) {
        return optionalClass;
      }
    }
    return Optional.empty();
  }

}