package com.itsoku.lambda;


import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.ref.WeakReference;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;

public class LambdaUtils {

    private static final Map<Class<?>, WeakReference<SerializedLambda>> FUNC_CACHE = new ConcurrentHashMap<>();

    /**
     * 解析 lambda 表达式, 该方法只是调用了 {@link SerializedLambda#resolve(SFunction)} 中的方法，在此基础上加了缓存。
     * 该缓存可能会在任意不定的时间被清除
     *
     * @param func 需要解析的 lambda 对象
     * @param <T>  类型，被调用的 Function 对象的目标类型
     * @return 返回解析后的结果
     * @see SerializedLambda#resolve(SFunction)
     */
    public static <T> SerializedLambda resolve(SFunction<T, ?> func) {
        Class<?> clazz = func.getClass();
        return Optional.ofNullable(FUNC_CACHE.get(clazz))
                .map(WeakReference::get)
                .orElseGet(() -> {
                    SerializedLambda lambda = SerializedLambda.resolve(func);
                    FUNC_CACHE.put(clazz, new WeakReference<>(lambda));
                    return lambda;
                });
    }

    public static <T> String getPropFromLambda(SFunction<T, ?> lambda) {
        return getPropertyNameFromLambda(resolve(lambda));
    }

    private static String getPropertyNameFromLambda(SerializedLambda resolve) {
        try {
            BeanInfo beanInfo = Introspector.getBeanInfo(resolve.getImplClass());
            PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
            if (propertyDescriptors != null) {
                for (PropertyDescriptor propertyDescriptor : propertyDescriptors) {
                    if (propertyDescriptor.getReadMethod().getName().equals(resolve.getImplMethodName())) {
                        return propertyDescriptor.getName();
                    }
                }
            }
            throw new IllegalPropertyException(resolve.getImplClassName(), resolve.getImplMethodName());
        } catch (IntrospectionException e) {
            throw new RuntimeException(e.getMessage(), e);
        }
    }
}