/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * 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/. */

// API class

package org.mozilla.javascript;

import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * Factory class that Rhino runtime uses to create new {@link Context} instances. A <code>
 * ContextFactory</code> can also notify listeners about context creation and release.
 *
 * <p>When the Rhino runtime needs to create new {@link Context} instance during execution of {@link
 * Context#enter()} or {@link Context}, it will call {@link #makeContext()} of the current global
 * ContextFactory. See {@link #getGlobal()} and {@link #initGlobal(ContextFactory)}.
 *
 * <p>It is also possible to use explicit ContextFactory instances for Context creation. This is
 * useful to have a set of independent Rhino runtime instances under single JVM. See {@link
 * #call(ContextAction)}.
 *
 * <p>The following example demonstrates Context customization to terminate scripts running more
 * then 10 seconds and to provide better compatibility with JavaScript code using MSIE-specific
 * features.
 *
 * <pre>
 * import org.mozilla.javascript.*;
 *
 * class MyFactory extends ContextFactory
 * {
 *
 *     // Custom {@link Context} to store execution time.
 *     private static class MyContext extends Context
 *     {
 *         long startTime;
 *     }
 *
 *     static {
 *         // Initialize GlobalFactory with custom factory
 *         ContextFactory.initGlobal(new MyFactory());
 *     }
 *
 *     // Override {@link #makeContext()}
 *     protected Context makeContext()
 *     {
 *         MyContext cx = new MyContext();
 *         // Make Rhino runtime to call observeInstructionCount
 *         // each 10000 bytecode instructions
 *         cx.setInstructionObserverThreshold(10000);
 *         return cx;
 *     }
 *
 *     // Override {@link #hasFeature(Context, int)}
 *     public boolean hasFeature(Context cx, int featureIndex)
 *     {
 *         // Turn on maximum compatibility with MSIE scripts
 *         switch (featureIndex) {
 *             case {@link Context#FEATURE_NON_ECMA_GET_YEAR}:
 *                 return true;
 *
 *             case {@link Context#FEATURE_MEMBER_EXPR_AS_FUNCTION_NAME}:
 *                 return true;
 *
 *             case {@link Context#FEATURE_RESERVED_KEYWORD_AS_IDENTIFIER}:
 *                 return true;
 *
 *             case {@link Context#FEATURE_PARENT_PROTO_PROPERTIES}:
 *                 return false;
 *         }
 *         return super.hasFeature(cx, featureIndex);
 *     }
 *
 *     // Override {@link #observeInstructionCount(Context, int)}
 *     protected void observeInstructionCount(Context cx, int instructionCount)
 *     {
 *         MyContext mcx = (MyContext)cx;
 *         long currentTime = System.currentTimeMillis();
 *         if (currentTime - mcx.startTime &gt; 10*1000) {
 *             // More then 10 seconds from Context creation time:
 *             // it is time to stop the script.
 *             // Throw Error instance to ensure that script will never
 *             // get control back through catch or finally.
 *             throw new Error();
 *         }
 *     }
 *
 *     // Override {@link #doTopCall(Callable,
 * Context, Scriptable,
 * Scriptable, Object[])}
 *     protected Object doTopCall(Callable callable,
 *                                Context cx, Scriptable scope,
 *                                Scriptable thisObj, Object[] args)
 *     {
 *         MyContext mcx = (MyContext)cx;
 *         mcx.startTime = System.currentTimeMillis();
 *
 *         return super.doTopCall(callable, cx, scope, thisObj, args);
 *     }
 *
 * }
 * </pre>
 */
public class ContextFactory {
    private static volatile boolean hasCustomGlobal;
    private static ContextFactory global = new ContextFactory();

    private volatile boolean sealed;

    private final Object listenersLock = new Object();
    private volatile Object listeners;
    private boolean disabledListening;
    private ClassLoader applicationClassLoader;

    /** Listener of {@link Context} creation and release events. */
    public interface Listener {
        /** Notify about newly created {@link Context} object. */
        public void contextCreated(Context cx);

        /**
         * Notify that the specified {@link Context} instance is no longer associated with the
         * current thread.
         */
        public void contextReleased(Context cx);
    }

    /**
     * Get global ContextFactory.
     *
     * @see #hasExplicitGlobal()
     * @see #initGlobal(ContextFactory)
     */
    public static ContextFactory getGlobal() {
        return global;
    }

    /**
     * Check if global factory was set. Return true to indicate that {@link
     * #initGlobal(ContextFactory)} was already called and false to indicate that the global factory
     * was not explicitly set.
     *
     * @see #getGlobal()
     * @see #initGlobal(ContextFactory)
     */
    public static boolean hasExplicitGlobal() {
        return hasCustomGlobal;
    }

    /**
     * Set global ContextFactory. The method can only be called once.
     *
     * @see #getGlobal()
     * @see #hasExplicitGlobal()
     */
    public static synchronized void initGlobal(ContextFactory factory) {
        if (factory == null) {
            throw new IllegalArgumentException();
        }
        if (hasCustomGlobal) {
            throw new IllegalStateException();
        }
        hasCustomGlobal = true;
        global = factory;
    }

    public interface GlobalSetter {
        public void setContextFactoryGlobal(ContextFactory factory);

        public ContextFactory getContextFactoryGlobal();
    }

    public static synchronized GlobalSetter getGlobalSetter() {
        if (hasCustomGlobal) {
            throw new IllegalStateException();
        }
        hasCustomGlobal = true;
        class GlobalSetterImpl implements GlobalSetter {
            @Override
            public void setContextFactoryGlobal(ContextFactory factory) {
                global = factory == null ? new ContextFactory() : factory;
            }

            @Override
            public ContextFactory getContextFactoryGlobal() {
                return global;
            }
        }
        return new GlobalSetterImpl();
    }

    /**
     * Create new {@link Context} instance to be associated with the current thread. This is a
     * callback method used by Rhino to create {@link Context} instance when it is necessary to
     * associate one with the current execution thread. <code>makeContext()</code> is allowed to
     * call {@link Context#seal(Object)} on the result to prevent {@link Context} changes by hostile
     * scripts or applets.
     */
    protected Context makeContext() {
        return new Context(this);
    }

    /**
     * Implementation of {@link Context#hasFeature(int featureIndex)}. This can be used to customize
     * {@link Context} without introducing additional subclasses.
     */
    protected boolean hasFeature(Context cx, int featureIndex) {
        int version;
        switch (featureIndex) {
            case Context.FEATURE_NON_ECMA_GET_YEAR:
                /*
                 * During the great date rewrite of 1.3, we tried to track the
                 * evolving ECMA standard, which then had a definition of
                 * getYear which always subtracted 1900.  Which we
                 * implemented, not realizing that it was incompatible with
                 * the old behavior...  now, rather than thrash the behavior
                 * yet again, we've decided to leave it with the - 1900
                 * behavior and point people to the getFullYear method.  But
                 * we try to protect existing scripts that have specified a
                 * version...
                 */
                version = cx.getLanguageVersion();
                return (version == Context.VERSION_1_0
                        || version == Context.VERSION_1_1
                        || version == Context.VERSION_1_2);

            case Context.FEATURE_MEMBER_EXPR_AS_FUNCTION_NAME:
                return false;

            case Context.FEATURE_RESERVED_KEYWORD_AS_IDENTIFIER:
                return true;

            case Context.FEATURE_TO_STRING_AS_SOURCE:
                version = cx.getLanguageVersion();
                return version == Context.VERSION_1_2;

            case Context.FEATURE_PARENT_PROTO_PROPERTIES:
                return true;

            case Context.FEATURE_E4X:
                version = cx.getLanguageVersion();
                return (version == Context.VERSION_DEFAULT || version >= Context.VERSION_1_6);

            case Context.FEATURE_DYNAMIC_SCOPE:
                return false;

            case Context.FEATURE_STRICT_VARS:
                return false;

            case Context.FEATURE_STRICT_EVAL:
                return false;

            case Context.FEATURE_LOCATION_INFORMATION_IN_ERROR:
                return false;

            case Context.FEATURE_STRICT_MODE:
                return false;

            case Context.FEATURE_WARNING_AS_ERROR:
                return false;

            case Context.FEATURE_ENHANCED_JAVA_ACCESS:
                return false;

            case Context.FEATURE_V8_EXTENSIONS:
                return true;

            case Context.FEATURE_OLD_UNDEF_NULL_THIS:
                return cx.getLanguageVersion() <= Context.VERSION_1_7;

            case Context.FEATURE_ENUMERATE_IDS_FIRST:
                return cx.getLanguageVersion() >= Context.VERSION_ES6;

            case Context.FEATURE_THREAD_SAFE_OBJECTS:
                return false;

            case Context.FEATURE_INTEGER_WITHOUT_DECIMAL_PLACE:
                return false;

            case Context.FEATURE_LITTLE_ENDIAN:
                return false;

            case Context.FEATURE_ENABLE_XML_SECURE_PARSING:
                return true;

            case Context.FEATURE_ENABLE_JAVA_MAP_ACCESS:
                return false;
        }
        // It is a bug to call the method with unknown featureIndex
        throw new IllegalArgumentException(String.valueOf(featureIndex));
    }

    private static boolean isDom3Present() {
        Class<?> nodeClass = Kit.classOrNull("org.w3c.dom.Node");
        if (nodeClass == null) return false;
        // Check to see whether DOM3 is present; use a new method defined in
        // DOM3 that is vital to our implementation
        try {
            nodeClass.getMethod("getUserData", new Class<?>[] {String.class});
            return true;
        } catch (NoSuchMethodException e) {
            return false;
        }
    }

    /**
     * Provides a default {@link org.mozilla.javascript.xml.XMLLib.Factory XMLLib.Factory} to be
     * used by the <code>Context</code> instances produced by this factory. See {@link
     * Context#getE4xImplementationFactory} for details.
     *
     * <p>May return null, in which case E4X functionality is not supported in Rhino.
     *
     * <p>The default implementation now prefers the DOM3 E4X implementation.
     */
    protected org.mozilla.javascript.xml.XMLLib.Factory getE4xImplementationFactory() {
        // Must provide default implementation, rather than abstract method,
        // so that past implementors of ContextFactory do not fail at runtime
        // upon invocation of this method.
        // Note that the default implementation returns null if we
        // neither have XMLBeans nor a DOM3 implementation present.

        if (isDom3Present()) {
            return org.mozilla.javascript.xml.XMLLib.Factory.create(
                    "org.mozilla.javascript.xmlimpl.XMLLibImpl");
        }
        return null;
    }

    /**
     * Create class loader for generated classes. This method creates an instance of the default
     * implementation of {@link GeneratedClassLoader}. Rhino uses this interface to load generated
     * JVM classes when no {@link SecurityController} is installed. Application can override the
     * method to provide custom class loading.
     */
    protected GeneratedClassLoader createClassLoader(final ClassLoader parent) {
        return AccessController.doPrivileged(
                new PrivilegedAction<DefiningClassLoader>() {
                    @Override
                    public DefiningClassLoader run() {
                        return new DefiningClassLoader(parent);
                    }
                });
    }

    /**
     * Get ClassLoader to use when searching for Java classes. Unless it was explicitly initialized
     * with {@link #initApplicationClassLoader(ClassLoader)} the method returns null to indicate
     * that Thread.getContextClassLoader() should be used.
     */
    public final ClassLoader getApplicationClassLoader() {
        return applicationClassLoader;
    }

    /**
     * Set explicit class loader to use when searching for Java classes.
     *
     * @see #getApplicationClassLoader()
     */
    public final void initApplicationClassLoader(ClassLoader loader) {
        if (loader == null) throw new IllegalArgumentException("loader is null");
        if (!Kit.testIfCanLoadRhinoClasses(loader))
            throw new IllegalArgumentException("Loader can not resolve Rhino classes");

        if (this.applicationClassLoader != null)
            throw new IllegalStateException("applicationClassLoader can only be set once");
        checkNotSealed();

        this.applicationClassLoader = loader;
    }

    /**
     * Execute top call to script or function. When the runtime is about to execute a script or
     * function that will create the first stack frame with scriptable code, it calls this method to
     * perform the real call. In this way execution of any script happens inside this function.
     */
    protected Object doTopCall(
            Callable callable, Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
        Object result = callable.call(cx, scope, thisObj, args);
        return result instanceof ConsString ? result.toString() : result;
    }

    /**
     * Implementation of {@link Context#observeInstructionCount(int instructionCount)}. This can be
     * used to customize {@link Context} without introducing additional subclasses.
     */
    protected void observeInstructionCount(Context cx, int instructionCount) {}

    protected void onContextCreated(Context cx) {
        Object listeners = this.listeners;
        for (int i = 0; ; ++i) {
            Listener l = (Listener) Kit.getListener(listeners, i);
            if (l == null) break;
            l.contextCreated(cx);
        }
    }

    protected void onContextReleased(Context cx) {
        Object listeners = this.listeners;
        for (int i = 0; ; ++i) {
            Listener l = (Listener) Kit.getListener(listeners, i);
            if (l == null) break;
            l.contextReleased(cx);
        }
    }

    public final void addListener(Listener listener) {
        checkNotSealed();
        synchronized (listenersLock) {
            if (disabledListening) {
                throw new IllegalStateException();
            }
            listeners = Kit.addListener(listeners, listener);
        }
    }

    public final void removeListener(Listener listener) {
        checkNotSealed();
        synchronized (listenersLock) {
            if (disabledListening) {
                throw new IllegalStateException();
            }
            listeners = Kit.removeListener(listeners, listener);
        }
    }

    /** The method is used only to implement Context.disableStaticContextListening() */
    final void disableContextListening() {
        checkNotSealed();
        synchronized (listenersLock) {
            disabledListening = true;
            listeners = null;
        }
    }

    /**
     * Checks if this is a sealed ContextFactory.
     *
     * @see #seal()
     */
    public final boolean isSealed() {
        return sealed;
    }

    /**
     * Seal this ContextFactory so any attempt to modify it like to add or remove its listeners will
     * throw an exception.
     *
     * @see #isSealed()
     */
    public final void seal() {
        checkNotSealed();
        sealed = true;
    }

    protected final void checkNotSealed() {
        if (sealed) throw new IllegalStateException();
    }

    /**
     * Call {@link ContextAction#run(Context cx)} using the {@link Context} instance associated with
     * the current thread. If no Context is associated with the thread, then {@link #makeContext()}
     * will be called to construct new Context instance. The instance will be temporary associated
     * with the thread during call to {@link ContextAction#run(Context)}.
     *
     * @see ContextFactory#call(ContextAction)
     * @see Context#call(ContextFactory factory, Callable callable, Scriptable scope, Scriptable
     *     thisObj, Object[] args)
     */
    public final <T> T call(ContextAction<T> action) {
        return Context.call(this, action);
    }

    /**
     * Get a context associated with the current thread, creating one if need be. The Context stores
     * the execution state of the JavaScript engine, so it is required that the context be entered
     * before execution may begin. Once a thread has entered a Context, then getCurrentContext() may
     * be called to find the context that is associated with the current thread.
     *
     * <p>Calling <code>enterContext()</code> will return either the Context currently associated
     * with the thread, or will create a new context and associate it with the current thread. Each
     * call to <code>enterContext()</code> must have a matching call to {@link Context#exit()}.
     *
     * <pre>
     *      Context cx = contextFactory.enterContext();
     *      try {
     *          ...
     *          cx.evaluateString(...);
     *      } finally {
     *          Context.exit();
     *      }
     * </pre>
     *
     * Instead of using <code>enterContext()</code>, <code>exit()</code> pair consider using {@link
     * #call(ContextAction)} which guarantees proper association of Context instances with the
     * current thread. With this method the above example becomes:
     *
     * <pre>
     *      ContextFactory.call(new ContextAction() {
     *          public Object run(Context cx) {
     *              ...
     *              cx.evaluateString(...);
     *              return null;
     *          }
     *      });
     * </pre>
     *
     * @return a Context associated with the current thread
     * @see Context#getCurrentContext()
     * @see Context#exit()
     * @see #call(ContextAction)
     */
    public Context enterContext() {
        return enterContext(null);
    }

    /**
     * @deprecated use {@link #enterContext()} instead
     * @return a Context associated with the current thread
     */
    @Deprecated
    public final Context enter() {
        return enterContext(null);
    }

    /** @deprecated Use {@link Context#exit()} instead. */
    @Deprecated
    public final void exit() {
        Context.exit();
    }

    /**
     * Get a Context associated with the current thread, using the given Context if need be.
     *
     * <p>The same as <code>enterContext()</code> except that <code>cx</code> is associated with the
     * current thread and returned if the current thread has no associated context and <code>cx
     * </code> is not associated with any other thread.
     *
     * @param cx a Context to associate with the thread if possible
     * @return a Context associated with the current thread
     * @see #enterContext()
     * @see #call(ContextAction)
     * @throws IllegalStateException if <code>cx</code> is already associated with a different
     *     thread
     */
    public final Context enterContext(Context cx) {
        return Context.enter(cx, this);
    }
}
