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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.

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/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.javascript.engine;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import org.mozilla.javascript.Context;

/**
 * 
 * This is an implementation of the standard Java "ScriptEngine" for Rhino. If the Rhino engine
 * (typically in the form of the "rhino-engine" JAR) is in the classpath, then this script
 * engine will be activated.
 * 
 * 
 * See the list of constants in this class for the list of language names, file extensions, and
 * MIME types that this engine supports. This list is essentially the same as the list supported
 * in the Nashorn script engine that was included in Java 8.
 * 
 * 
 * Since this engine and Nashorn support the same language and file extensions, then unless
 * you are sure you are running in an environment that has Nashorn, the best way to get this
 * engine is to call ScriptEngine.getEngineByName("rhino") to ask for Rhino directly.
 * 
 */
public class RhinoScriptEngineFactory
  implements ScriptEngineFactory {

  public static final String NAME = "rhino";
  private static final String LANGUAGE = "javascript";
  private static final List NAMES =
      Arrays.asList("rhino", "Rhino", "javascript", "JavaScript");
  private static final List EXTENSIONS =
      Collections.singletonList("js");
  private static final List MIME_TYPES =
      Arrays.asList("application/javascript", "application/ecmascript",
          "text/javascript", "text/ecmascript");
  private static final String LANGUAGE_VERSION =
      String.valueOf(RhinoScriptEngine.DEFAULT_LANGUAGE_VERSION);

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

  @Override
  public String getEngineVersion() {
    try (Context cx = Context.enter()) {
      String v = cx.getImplementationVersion();
      return (v == null ? "unknown" : v);
    }
  }

  @Override
  public List getExtensions() {
    return EXTENSIONS;
  }

  @Override
  public List getMimeTypes() {
    return MIME_TYPES;
  }

  @Override
  public List 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.ENGINE:
        return getEngineName();
      case ScriptEngine.ENGINE_VERSION:
        return getEngineVersion();
      case ScriptEngine.LANGUAGE:
        return getLanguageName();
      case ScriptEngine.LANGUAGE_VERSION:
        return getLanguageVersion();
      case ScriptEngine.NAME:
        return NAME;
      case "THREADING":
        // Engines are explicitly not thread-safe
        return null;
      default:
        return null;
    }
  }

  @Override
  public String getMethodCallSyntax(String obj, String m, String... args) {
    StringBuilder sb = new StringBuilder();
    sb.append(obj).append('.').append(m).append('(');
    for (int i = 0; i < args.length; i++) {
      if (i > 0) {
        sb.append(',');
      }
      sb.append(args[i]);
    }
    sb.append(");");
    return sb.toString();
  }

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

  @Override
  public String getProgram(String... statements) {
    StringBuilder sb = new StringBuilder();
    for (String stmt : statements) {
      sb.append(stmt).append(";\n");
    }
    return sb.toString();
  }

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