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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.view.resolver;

import com.amazon.ask.mvc.view.BaseView;
import com.fasterxml.jackson.databind.ObjectMapper;

import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.SimpleBindings;
import java.util.Map;

import static com.amazon.ask.util.ValidationUtils.assertNotNull;

/**
 * Renders a response using a {@link ScriptEngine}
 */
public class ScriptEngineView extends BaseView {
    protected final ScriptEngine scriptEngine;
    protected final String script;
    protected final String renderFunction;
    protected final String renderObject;

    public ScriptEngineView(ScriptEngine scriptEngine, String script, String renderObject, String renderFunction, ObjectMapper mapper) throws Exception {
        super(mapper);
        this.scriptEngine = assertNotNull(scriptEngine, "scriptEngine");
        this.script = assertNotNull(script, "script");
        this.renderObject = renderObject;
        this.renderFunction = renderFunction;

        if (renderFunction != null) {
            // render logic is attached to a global function or object
            // script needs to be eval'ed once so its functions and objects are available in the engine state for invocation
            if (scriptEngine instanceof Invocable) {
                this.scriptEngine.eval(script);
            } else {
                throw new IllegalArgumentException("ScriptEngine must be an Invocable if renderFunction or renderObject are specified");
            }
        }
    }

    @Override
    protected String renderInternal(Map model) throws Exception {
        SimpleBindings bindings = new SimpleBindings(model);
        Object result;
        if (renderFunction == null && renderObject == null) {
            // result of script is the response, no method is invoked and the model attributes are bounded globally
            result = scriptEngine.eval(script, bindings);
        } else {
            if (renderObject != null) {
                Object thiz = scriptEngine.eval(renderObject);
                result = ((Invocable) scriptEngine).invokeMethod(thiz, renderFunction, bindings);
            } else {
                result = ((Invocable) scriptEngine).invokeFunction(renderFunction, bindings);
            }
        }

        return toJson(result);
    }

    /**
     * By default we assume the result is a json string, but we may want to override that.
     *
     * @param result rendered by the view
     * @return JSON string of view output
     * @throws Exception if the response is invalid
     */
    protected String toJson(Object result) throws Exception {
        return (String) result;
    }
}