com.amazon.ask.mvc.annotation.plugin.AutoPredicate Maven / Gradle / Ivy

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/*
    Copyright 2018 Amazon.com, Inc. or its affiliates. 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. A copy of the License is located at

        http://aws.amazon.com/apache2.0/

    or in the "license" file accompanying this file. This file 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 com.amazon.ask.mvc.annotation.plugin;

import com.amazon.ask.dispatcher.request.handler.HandlerInput;
import com.amazon.ask.interaction.Utils;
import com.amazon.ask.mvc.annotation.condition.WhenDialogState;
import com.amazon.ask.mvc.annotation.condition.WhenSessionAttribute;
import com.amazon.ask.mvc.mapper.AnnotationContext;
import com.amazon.ask.mvc.plugin.PredicateResolver;

import java.lang.annotation.*;
import java.util.Optional;
import java.util.function.BiFunction;
import java.util.function.Predicate;
import java.util.stream.Stream;

/**
 * Added to annotations that make a mapping conditional, based on a predicate.
 *
 * @see WhenSessionAttribute
 * @see WhenDialogState
 */
@Target(ElementType.ANNOTATION_TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface AutoPredicate {
    Class> value();

    interface Plugin
        extends BiFunction> {
    }

    class Scanner implements PredicateResolver {
        @Override
        @SuppressWarnings("unchecked")
        public Optional> resolve(AnnotationContext context) {
            return context.scanAnnotations()
                .flatMap(annotation -> {
                    AutoPredicate meta = annotation.annotationType().getAnnotation(AutoPredicate.class);
                    if (meta != null) {
                        AutoPredicate.Plugin plugin = (AutoPredicate.Plugin) Utils.instantiate(meta.value());
                        return Stream.of(plugin.apply(context, annotation));
                    } else {
                        return Stream.empty();
                    }
                })
                .reduce(Predicate::and);
        }
    }
}