package cn.mb.cloud.common.sentinel.fallback;

import cn.mb.cloud.common.core.constant.enums.ErrorCodeConstants;
import cn.mb.cloud.common.core.util.ResponseData;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * 公共 Sentinel Feign 降级处理的安全替代实现。
 *
 * <p>依赖版本假定所有泛型返回类型均为 {@link Class}。对于
 * {@code Map<String, Object>} 等声明并不成立，其运行时类型为
 * {@link ParameterizedType}；此前转换失败会以 AssertionError 掩盖原始下游异常。</p>
 */
public class DefaultFeignFallback<T> implements MethodInterceptor {
    private static final Logger log = LoggerFactory.getLogger(DefaultFeignFallback.class);

    private final Class<T> targetType;
    private final String targetName;
    private final Throwable cause;

    public DefaultFeignFallback(Class<T> targetType, String targetName, Throwable cause) {
        this.targetType = targetType;
        this.targetName = targetName;
        this.cause = cause;
    }

    @Override
    public Object intercept(Object object, Method method, Object[] arguments, MethodProxy methodProxy) {
        log.error("FunFeignFallback:[{}.{}] serviceId:[{}] message:[{}]",
                targetType.getName(), method.getName(), targetName, cause == null ? null : cause.getMessage());

        Type declaredReturnType = method.getGenericReturnType();
        Class<?> returnType = rawType(declaredReturnType);
        Object data = defaultValue(returnType);

        // 仅显式声明返回 ResponseData 的方法可以返回 ResponseData 降级结果。
        // 在 Map/List 方法中返回该对象会导致 Feign 代理再次抛出 ClassCastException。
        if (ResponseData.class.equals(returnType)) {
            Type dataType = firstTypeArgument(declaredReturnType);
            return ResponseData.builder()
                    .code(ErrorCodeConstants.FAIL.getValue())
                    .msg("系统降级,请稍后再试！")
                    .data(defaultValue(rawType(dataType)))
                    .build();
        }
        return data;
    }

    private Type firstTypeArgument(Type type) {
        if (type instanceof ParameterizedType) {
            Type[] arguments = ((ParameterizedType) type).getActualTypeArguments();
            if (arguments.length > 0) return arguments[0];
        }
        return null;
    }

    private Class<?> rawType(Type type) {
        if (type instanceof Class<?>) return (Class<?>) type;
        if (type instanceof ParameterizedType) return rawType(((ParameterizedType) type).getRawType());
        return Object.class;
    }

    private Object defaultValue(Class<?> type) {
        if (List.class.isAssignableFrom(type)) return new ArrayList<Object>();
        if (Set.class.isAssignableFrom(type)) return new HashSet<Object>();
        if (Map.class.isAssignableFrom(type)) return new HashMap<Object, Object>();
        if (Boolean.class.equals(type) || boolean.class.equals(type)) return Boolean.FALSE;
        if (type.isPrimitive()) return primitiveDefault(type);
        return null;
    }

    private Object primitiveDefault(Class<?> type) {
        if (char.class.equals(type)) return Character.valueOf('\0');
        if (byte.class.equals(type)) return Byte.valueOf((byte) 0);
        if (short.class.equals(type)) return Short.valueOf((short) 0);
        if (int.class.equals(type)) return Integer.valueOf(0);
        if (long.class.equals(type)) return Long.valueOf(0L);
        if (float.class.equals(type)) return Float.valueOf(0F);
        if (double.class.equals(type)) return Double.valueOf(0D);
        return null;
    }
}