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 * The Universal Permissive License (UPL), Version 1.0
 *
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 * data (collectively the "Software"), free of charge and under any and all
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 * unmodified Software as contributed to or provided by such licensor, or (ii)
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 * (a) the Software, and
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 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
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 * Software and the Larger Work(s), and to sublicense the foregoing rights on
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package com.oracle.truffle.js.scriptengine;

import java.lang.ref.WeakReference;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Objects;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;

import org.graalvm.polyglot.Engine;

public final class GraalJSEngineFactory implements ScriptEngineFactory {

    private static final String ENGINE_NAME = "Graal.js";
    private static final String NAME = "javascript";
    private static final String LANGUAGE = "ECMAScript";
    private static final String LANGUAGE_VERSION = "ECMAScript 262 Edition 11";

    private static final String NASHORN_ENGINE_NAME = "Oracle Nashorn";
    private static final List<String> names;
    private static final List<String> mimeTypes;
    private static final List<String> extensions;

    public static final boolean RegisterAsNashornScriptEngineFactory = Boolean.getBoolean("graaljs.RegisterGraalJSAsNashorn");

    static {
        List<String> nameList = new ArrayList<>(Arrays.asList("Graal.js", "graal.js", "Graal-js", "graal-js", "Graal.JS", "Graal-JS", "GraalJS", "GraalJSPolyglot", "js", "JS", "JavaScript",
                        "javascript", "ECMAScript", "ecmascript"));
        List<String> mimeTypeList = new ArrayList<>(Arrays.asList("application/javascript", "application/ecmascript", "text/javascript", "text/ecmascript"));
        List<String> extensionList = new ArrayList<>(Arrays.asList("js", "mjs"));
        boolean java8 = System.getProperty("java.specification.version").compareTo("1.9") < 0;
        if (java8) {
            ScriptEngineFactory nashornFactory = getNashornEngineFactory();
            if (nashornFactory != null) {
                if (RegisterAsNashornScriptEngineFactory) {
                    nameList.addAll(nashornFactory.getNames());
                    mimeTypeList.addAll(nashornFactory.getMimeTypes());
                    extensionList.addAll(nashornFactory.getExtensions());
                }
                clearEngineFactory(nashornFactory);
            }
        }
        names = Collections.unmodifiableList(nameList);
        mimeTypes = Collections.unmodifiableList(mimeTypeList);
        extensions = Collections.unmodifiableList(extensionList);
    }

    private WeakReference<Engine> defaultEngine;
    private final Engine userDefinedEngine;

    public GraalJSEngineFactory() {
        this.defaultEngine = null; // lazy
        this.userDefinedEngine = null;
    }

    GraalJSEngineFactory(Engine engine) {
        this.userDefinedEngine = engine;
    }

    private static Engine createDefaultEngine() {
        return Engine.newBuilder().allowExperimentalOptions(true).build();
    }

    
Returns the underlying polyglot engine.
/**
     * Returns the underlying polyglot engine.
     */
    public Engine getPolyglotEngine() {
        if (userDefinedEngine != null) {
            return userDefinedEngine;
        } else {
            Engine engine = defaultEngine == null ? null : defaultEngine.get();
            if (engine == null) {
                engine = createDefaultEngine();
                defaultEngine = new WeakReference<>(engine);
            }
            return engine;
        }
    }

    @Override
    public String getEngineName() {
        return ENGINE_NAME;
    }

    @Override
    public String getEngineVersion() {
        return getPolyglotEngine().getVersion();
    }

    @Override
    public List<String> getExtensions() {
        return extensions;
    }

    @Override
    public List<String> getMimeTypes() {
        return mimeTypes;
    }

    @Override
    public List<String> getNames() {
        return names;
    }

    @Override
    public String getLanguageName() {
        return LANGUAGE;
    }

    @Override
    public String getLanguageVersion() {
        return LANGUAGE_VERSION;
    }

    @Override
    public Object getParameter(String key) {
        switch (key) {
            case ScriptEngine.NAME:
                return NAME;
            case ScriptEngine.ENGINE:
                return getEngineName();
            case ScriptEngine.ENGINE_VERSION:
                return getEngineVersion();
            case ScriptEngine.LANGUAGE:
                return getLanguageName();
            case ScriptEngine.LANGUAGE_VERSION:
                return getLanguageVersion();
            default:
                return null;
        }
    }

    @Override
    public GraalJSScriptEngine getScriptEngine() {
        return new GraalJSScriptEngine(this);
    }

    @Override
    public String getMethodCallSyntax(final String obj, final String method, final String... args) {
        Objects.requireNonNull(obj);
        Objects.requireNonNull(method);
        final StringBuilder sb = new StringBuilder().append(obj).append('.').append(method).append('(');
        final int len = args.length;

        if (len > 0) {
            Objects.requireNonNull(args[0]);
            sb.append(args[0]);
        }
        for (int i = 1; i < len; i++) {
            Objects.requireNonNull(args[i]);
            sb.append(',').append(args[i]);
        }
        sb.append(')');

        return sb.toString();
    }

    @Override
    public String getOutputStatement(final String toDisplay) {
        return "print(" + toDisplay + ")";
    }

    @Override
    public String getProgram(final String... statements) {
        final StringBuilder sb = new StringBuilder();

        for (final String statement : statements) {
            Objects.requireNonNull(statement);
            sb.append(statement).append(';');
        }

        return sb.toString();
    }

    private static ScriptEngineFactory getNashornEngineFactory() {
        for (ScriptEngineFactory factory : new ScriptEngineManager().getEngineFactories()) {
            if (NASHORN_ENGINE_NAME.equals(factory.getEngineName())) {
                return factory;
            }
        }
        return null;
    }

    private static void clearEngineFactory(ScriptEngineFactory factory) {
        assert factory != null;

        try {
            Class<?> clazz = factory.getClass();
            for (String immutableListFieldName : new String[]{"names", "mimeTypes", "extensions"}) {
                Field immutableListField = clazz.getDeclaredField(immutableListFieldName);
                immutableListField.setAccessible(true);
                Object immutableList = immutableListField.get(null);

                Class<?> unmodifiableListClazz = Class.forName("java.util.Collections$UnmodifiableList");
                Field unmodifiableListField = unmodifiableListClazz.getDeclaredField("list");
                unmodifiableListField.setAccessible(true);

                Class<?> unmodifiableCollectionClazz = Class.forName("java.util.Collections$UnmodifiableCollection");
                Field unmodifiableCField = unmodifiableCollectionClazz.getDeclaredField("c");
                unmodifiableCField.setAccessible(true);

                List<?> list = (List<?>) unmodifiableListField.get(immutableList);
                List<Object> filteredList = new ArrayList<>();

                for (Object item : list) {
                    if (!RegisterAsNashornScriptEngineFactory && item.toString().toLowerCase().equals("nashorn")) {
                        filteredList.add(item);
                    }
                }

                unmodifiableListField.set(immutableList, filteredList);
                unmodifiableCField.set(immutableList, filteredList);
            }
        } catch (NullPointerException | ClassNotFoundException | IllegalAccessException | IllegalArgumentException | NoSuchFieldException | SecurityException e) {
            System.err.println("Failed to clear engine names [" + factory.getEngineName() + "]");
            e.printStackTrace();
        }
    }
}