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The Alexa Skills Kit MVC Framework extends the existing ASK SDK, adding features for mapping requests to methods and rendering responses via view scripts and templates such as Nashorn Javascript and Freemarker. It also integrates with the ASK SDK Interaction Model Mapper framework to create a single environment where both the interaction model and business logic of skills can be managed as code packages.

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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.condition;

import com.amazon.ask.dispatcher.request.handler.HandlerInput;
import com.amazon.ask.interaction.Utils;
import com.amazon.ask.mvc.annotation.plugin.AutoPredicate;
import com.amazon.ask.mvc.mapper.AnnotationContext;

import java.lang.annotation.Documented;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import java.util.*;
import java.util.function.Predicate;

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * When added to a handler method, the method will be invoked only if one
 * of the following conditions is met:
 * 
 *     The attribute is in the session, its value is of type String and it is contained in the values list
 *     The attribute is not in the session (or it has a null value), and matchUndefinedValue is set to true
 * 
 */
@Documented
@Target(value = {METHOD, TYPE})
@Retention(value = RUNTIME)
@Repeatable(WhenSessionAttribute.Container.class)
@AutoPredicate(WhenSessionAttribute.Plugin.class)
public @interface WhenSessionAttribute {

    /**
     * @return the attribute name
     */
    String[] path();

    /**
     * @return possible attribute values
     */
    String[] hasValues() default {};

    /**
     * @return if the condition should match a null or missing value
     */
    boolean matchNull() default false;

    /**
     * Adds support for the {@link WhenSessionAttribute} predicate.
     */
    class Plugin implements AutoPredicate.Plugin {
        @Override
        public Predicate apply(AnnotationContext context, WhenSessionAttribute annotation) {
            final Set values = new HashSet<>(Arrays.asList(annotation.hasValues()));

            return input -> {
                Map session = input.getRequestEnvelope().getSession().getAttributes();
                String value = null;

                if (session != null) {
                    String[] path = annotation.path();

                    Map map = session;
                    for (int i = 0; i < path.length; i++) {
                        Object o = map.get(path[i]);

                        if (i + 1 < path.length) {
                            // not the last element
                            if (o instanceof Map) {
                                map = (Map) o;
                            } else {
                                break;
                            }
                        } else {
                            if (o instanceof String) {
                                // we found the value
                                value = (String) o;
                            } else {
                                break;
                            }
                        }
                    }
                }

                if (value == null) {
                    return annotation.matchNull();
                }

                return values.contains(value);
            };
        }
    }

    /**
     * Adds support for multiple {@link WhenSessionAttribute} predicates.
     */
    @Documented
    @Target(value = {METHOD, TYPE})
    @Retention(value = RUNTIME)
    @AutoPredicate(WhenSessionAttribute.Container.Plugin.class)
    @interface Container {
        /**
         * @return repeated {@link WhenSessionAttribute} annotations.
         */
        WhenSessionAttribute[] value();

        class Plugin implements AutoPredicate.Plugin {
            private static final WhenSessionAttribute.Plugin SINGLE = new WhenSessionAttribute.Plugin();
            @Override
            public Predicate apply(AnnotationContext context, Container container) {
                return Arrays.stream(container.value())
                    .map(whenSessionAttribute -> SINGLE.apply(context, whenSessionAttribute))
                    .reduce(Predicate::and)
                    .orElse(Utils.TRUE);
            }
        }
    }
}