/*
 * Copyright 2008-2009 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 * 
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 * 
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 * 
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * 
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package java.dyn;

import sun.dyn.util.MethodHandleInvoker;
import java.util.WeakHashMap;
import sun.reflect.Reflection;

/**
 * Static methods which control the linkage of invokedynamic call sites.
 * @author John Rose, JSR 292 EG
 */
public class Linkage {
    private Linkage() {}  // do not instantiate

    /**
     * Register a bootstrap method for use for a given caller class.
     * The method handle must be of a type equivalent to {@link Linkage#bootstrapInvokeDynamic}.
     * <p>
     * The operation will fail with an exception if any of the following conditions hold:
     * <ul>
     * <li>The caller of this method is in a different package than the {@code callerClass},
     *     and there is a security manager, and its {@code checkPermission} call throws
     *     when passed {@link LinkagePermission}("registerBootstrapMethod",callerClass).
     * <li>The given class already has a bootstrap method, either from an embedded
     *     {@code BootstrapInvokeDynamic} classfile attribute, or from a previous
     *     call to this method.
     * <li>The given class is already fully initialized.
     * <li>The given class is in the process of initialization, in another thread.
     * </ul>
     * Because of these rules, a class may install its own bootstrap method in
     * a static initializer.
     */
    public static
    void registerBootstrapMethod(Class callerClass, MethodHandle mh) {
        Class callc = Reflection.getCallerClass(2);
        checkPackagePrivilege(callc, callerClass, "registerBootstrapMethod");
        if (mh != null && mh.type() != BOOTSTRAP_METHOD_TYPE)
            throw new WrongMethodTypeException(mh.type().toString());
        synchronized (bootstrapMethods) {
            if (bootstrapMethods.containsKey(callerClass))
                throw new IllegalStateException("bootstrap method already declared in "+callerClass);
            bootstrapMethods.put(callerClass, mh);
        }
    }

    /**
     * Simplified version of registerBootstrapMethod for self-registration,
     * to be called from a static initializer.
     * Finds a static method of type (CallSite, Object[]) -> Object in the
     * caller's class, and installs it on the caller.
     * @throws IllegalArgumentException if there is no such method
     */
    public static
    void registerBootstrapMethod(String name) {
        Class callc = Reflection.getCallerClass(2);
        MethodHandle bootstrapMethod = 
            MethodHandles.findStaticFrom(callc, callc, name, BOOTSTRAP_METHOD_TYPE);
        if (bootstrapMethod == null)
            throw new IllegalArgumentException("cannot find bootstrap method: "+name);
        Linkage.registerBootstrapMethod(callc, bootstrapMethod);
    }
    
    /**
     * Report the bootstrap method registered for a given class.
     * Returns null if the class has never yet registered a bootstrap method,
     * or if the class has explicitly registered a null bootstrap method.
     * Only callers privileged to set the bootstrap method may inquire
     * about it, because a bootstrap method is potentially a back-door entry
     * point into its class.
     */
    public static
    MethodHandle getBootstrapMethod(Class callerClass) {
        Class callc = Reflection.getCallerClass(2);
        checkPackagePrivilege(callc, callerClass, "registerBootstrapMethod");
        synchronized (bootstrapMethods) {
            return bootstrapMethods.get(callerClass);
        }
    }

    /** The type of any bootstrap method is (CallSite,Object...)Object.
     *  The varargs marker is required.
     */
    public static final MethodType BOOTSTRAP_METHOD_TYPE
            = MethodType.make(Object.class,
                              CallSite.class, Object[].class);

    private static MethodHandleInvoker bootstrapMethodInvoker;

    private static final WeakHashMap<Class, MethodHandle> bootstrapMethods =
            new WeakHashMap<Class, MethodHandle>();

    /**
     * Determine if the caller class has declared or registered its own bootstrap method.
     * If so, delegate this call to it.  Otherwise, throw an IncompatibleClassChangeError.
     * <p>
     * This routine, or an equivalent sequence of actions, is called from the
     * JVM when an {@code invokedynamic} instruction is executed
     * but its call site is unlinked (has a null target method).
     * <p>
     * This routine can be called from Java code whether or not the call site
     * currently has a target, and will invoke the bootstrap method regardless
     * of he call site's linkage state.
     * <p>
     * Although invoking the bootstrap method does not in and of itself cause
     * state change in the call site, the actions eventually performed by
     * the bootstrap method may include installed a new target on the call site.
     * <p>
     * Note that linkage state changes are individually atomic, but are not
     * serialized in any way with respect to calls to the bootstrap method,
     * or executions of the {@code invokedynamic} instruction.  Therefore,
     * an {@code invokedynamic} call site may be linked several times if
     * several threads concurrently execute it in an unlinked state.
     * It is up to the user-defined bootstrap method to make sure this
     * race condition is resolved safely, either by performing linkage
     * decisions under suitable locks (as the JVM does) or by ensuring
     * that all racing threads come to the same conclusion, and independently
     * install equivalent target methods.
     */
    public static
    Object bootstrapInvokeDynamic(CallSite site, Object... arguments) {
        Class callerClass = site.callerClass();
        MethodHandle mh;
        synchronized (bootstrapMethods) {
            mh = bootstrapMethods.get(callerClass);
        }
        if (mh == null)
            throw new IllegalStateException("no bootstrap method declared in "+callerClass);

        System.out.println(site+": calling bootstrap "+mh); // FIXME
        if (bootstrapMethodInvoker == null)
            bootstrapMethodInvoker = MethodHandleInvoker.make(BOOTSTRAP_METHOD_TYPE);
        return bootstrapMethodInvoker.invoke(mh, site, arguments);
    }

    /**
     * Invalidate all <code>invokedynamic</code> call sites everywhere.
     * <p>
     * When this method returns, every <code>invokedynamic</code> instruction
     * will invoke its bootstrap method on next call.
     * <p>
     * It is unspecified whether call sites already known to the Java
     * code will continue to be associated with <code>invokedynamic</code>
     * instructions.  If any call site is still so associated, its
     * {@link CallSite#getTarget()} method is guaranteed to return null
     * the invalidation operation completes.
     * <p>
     * Invalidation operations are likely to be slow.  Use them sparingly.
     */
    public static
    Object invalidateAll() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkPermission(new LinkagePermission("invalidateAll"));
        }
        throw new UnsupportedOperationException("NYI");
    }

    /**
     * Invalidate all <code>invokedynamic</code> call sites associated
     * with the given class.
     * (These are exactly those sites which report the given class
     * via the {@link CallSite#callerClass()} method.)
     * <p>
     * When this method returns, every matching <code>invokedynamic</code>
     * instruction will invoke its bootstrap method on next call.
     * <p>
     * For additional semantics of call site invalidation,
     * see {@link #invalidateAll()}.
     */
    public static
    Object invalidateCallerClass(Class<?> callerClass) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkPermission(new LinkagePermission("invalidateAll", callerClass));
        }
        throw new UnsupportedOperationException("NYI");
    }

    /**
     * Ensure the requesting class have privileges to perform invokedynamic
     * linkage operations on subjectClass.  True if requestingClass is
     * null (meaning the request originates from the JVM) or if the
     * classes are in the same package and have consistent class loaders.
     * (The subject class loader must be identical with or be a child of
     * the requesting class loader.)
     * @param requestingClass
     * @param subjectClass
     */
    // FIXME: factor this logic into sun.dyn.util.VerifyAccess
    static void checkPackagePrivilege(Class requestingClass, Class subjectClass,
                                    String permissionName) {
        if (requestingClass == null)  return;
        if (requestingClass == subjectClass)  return;
        SecurityManager security = System.getSecurityManager();
        if (security == null)  return;  // open season
        ClassLoader rcl = requestingClass.getClassLoader();
        ClassLoader scl = subjectClass.getClassLoader();
        if (isParent(rcl, scl)) {
            String rn = requestingClass.getName();
            if (rn.startsWith("java.dyn."))  return;
            String sn = subjectClass.getName();
            if (samePackage(rn, sn))  return;
        }
        security.checkPermission(new LinkagePermission(permissionName, requestingClass));
    }
    
    static
    MethodHandle findBootstrapMethod(Class callerClass, Class searchBootstrapClass) {
        if (searchBootstrapClass != null)  throw new UnsupportedOperationException("NYI");
        MethodHandle mh = getBootstrapMethod(callerClass);
        System.out.println("reporting bootstrap method to JVM: "+mh); //FIXME
        return mh;
    }

    private static boolean isParent(ClassLoader rcl, ClassLoader scl) {
        while (scl != null && scl != rcl)
            scl = scl.getParent();
        return (scl == rcl);
    }

    private static boolean samePackage(String rn, String sn) {
        assert((rn.indexOf('/') & sn.indexOf('/')) < 0);  // no bytecode names
        int lastDot  = rn.lastIndexOf('.');
        if (lastDot != sn.lastIndexOf('.'))  return false;
        return rn.startsWith(sn.substring(0, lastDot+1));
    }

}