/*
 * Copyright (c) 2017, Oracle and/or its affiliates. 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.lang.invoke;

import sun.invoke.util.Wrapper;

import java.lang.invoke.AbstractConstantGroup.BSCIWithCache;
import java.util.Arrays;

import static java.lang.invoke.BootstrapCallInfo.makeBootstrapCallInfo;
import static java.lang.invoke.ConstantGroup.makeConstantGroup;
import static java.lang.invoke.MethodHandleNatives.*;
import static java.lang.invoke.MethodHandleStatics.TRACE_METHOD_LINKAGE;
import static java.lang.invoke.MethodHandles.Lookup;
import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;

final class BootstrapMethodInvoker {
    /**
     * Factored code for invoking a bootstrap method for invokedynamic
     * or a dynamic constant.
     * @param resultType the expected return type (either CallSite or a constant type)
     * @param bootstrapMethod the BSM to call
     * @param name the method name or constant name
     * @param type the method type or constant type
     * @param info information passed up from the JVM, to derive static arguments
     * @param callerClass the class containing the resolved method call or constant load
     * @param <T> the expected return type
     * @return the expected value, either a CallSite or a constant value
     */
    static <T> T invoke(Class<T> resultType,
                        MethodHandle bootstrapMethod,
                        // Callee information:
                        String name, Object type,
                        // Extra arguments for BSM, if any:
                        Object info,
                        // Caller information:
                        Class<?> callerClass) {
        MethodHandles.Lookup caller = IMPL_LOOKUP.in(callerClass);
        Object result;
        boolean pullMode = isPullModeBSM(bootstrapMethod);  // default value is false
        boolean vmIsPushing = !staticArgumentsPulled(info); // default value is true
        MethodHandle pullModeBSM;
        // match the VM with the BSM
        if (vmIsPushing) {
            // VM is pushing arguments at us
            pullModeBSM = null;
            if (pullMode) {
                bootstrapMethod = Adapters.pushMePullYou(bootstrapMethod, true);
            }
        } else {
            // VM wants us to pull args from it
            pullModeBSM = pullMode ? bootstrapMethod :
                    Adapters.pushMePullYou(bootstrapMethod, false);
            bootstrapMethod = null;
        }
        try {
            info = maybeReBox(info);
            if (info == null) {
                // VM is allowed to pass up a null meaning no BSM args
                result = bootstrapMethod.invoke(caller, name, type);
            }
            else if (!info.getClass().isArray()) {
                // VM is allowed to pass up a single BSM arg directly
                result = bootstrapMethod.invoke(caller, name, type, info);
            }
            else if (info.getClass() == int[].class) {
                // VM is allowed to pass up a pair {argc, index}
                // referring to 'argc' BSM args at some place 'index'
                // in the guts of the VM (associated with callerClass).
                // The format of this index pair is private to the
                // handshake between the VM and this class only.
                // This supports "pulling" of arguments.
                // The VM is allowed to do this for any reason.
                // The code in this method makes up for any mismatches.
                BootstrapCallInfo<Object> bsci
                    = new VM_BSCI<>(bootstrapMethod, name, type, caller, (int[])info);
                // Pull-mode API is (Lookup, BootstrapCallInfo) -> Object
                result = pullModeBSM.invoke(caller, bsci);
            }
            else {
                // VM is allowed to pass up a full array of resolved BSM args
                Object[] argv = (Object[]) info;
                maybeReBoxElements(argv);
                switch (argv.length) {
                    case 0:
                        result = bootstrapMethod.invoke(caller, name, type);
                        break;
                    case 1:
                        result = bootstrapMethod.invoke(caller, name, type,
                                                        argv[0]);
                        break;
                    case 2:
                        result = bootstrapMethod.invoke(caller, name, type,
                                                        argv[0], argv[1]);
                        break;
                    case 3:
                        result = bootstrapMethod.invoke(caller, name, type,
                                                        argv[0], argv[1], argv[2]);
                        break;
                    case 4:
                        result = bootstrapMethod.invoke(caller, name, type,
                                                        argv[0], argv[1], argv[2], argv[3]);
                        break;
                    case 5:
                        result = bootstrapMethod.invoke(caller, name, type,
                                                        argv[0], argv[1], argv[2], argv[3], argv[4]);
                        break;
                    case 6:
                        result = bootstrapMethod.invoke(caller, name, type,
                                                        argv[0], argv[1], argv[2], argv[3], argv[4], argv[5]);
                        break;
                    default:
                        final int NON_SPREAD_ARG_COUNT = 3;  // (caller, name, type)
                        final int MAX_SAFE_SIZE = MethodType.MAX_MH_ARITY / 2 - NON_SPREAD_ARG_COUNT;
                        if (argv.length >= MAX_SAFE_SIZE) {
                            // to be on the safe side, use invokeWithArguments which handles jumbo lists
                            Object[] newargv = new Object[NON_SPREAD_ARG_COUNT + argv.length];
                            newargv[0] = caller;
                            newargv[1] = name;
                            newargv[2] = type;
                            System.arraycopy(argv, 0, newargv, NON_SPREAD_ARG_COUNT, argv.length);
                            result = bootstrapMethod.invokeWithArguments(newargv);
                            break;
                        }
                        MethodType invocationType = MethodType.genericMethodType(NON_SPREAD_ARG_COUNT + argv.length);
                        MethodHandle typedBSM = bootstrapMethod.asType(invocationType);
                        MethodHandle spreader = invocationType.invokers().spreadInvoker(NON_SPREAD_ARG_COUNT);
                        result = spreader.invokeExact(typedBSM, (Object) caller, (Object) name, type, argv);
                }
            }
            if (resultType.isPrimitive()) {
                // Non-reference conversions are more than just plain casts.
                // By pushing the value through a funnel of the form (T x)->x,
                // the boxed result can be widened as needed.  See MH::asType.
                MethodHandle funnel = MethodHandles.identity(resultType);
                result = funnel.invoke(result);
                // Now it is the wrapper type for resultType.
                resultType = Wrapper.asWrapperType(resultType);
            }
            return resultType.cast(result);
        }
        catch (Error e) {
            // Pass through an Error, including BootstrapMethodError, any other
            // form of linkage error, such as IllegalAccessError if the bootstrap
            // method is inaccessible, or say ThreadDeath/OutOfMemoryError
            // See the "Linking Exceptions" section for the invokedynamic
            // instruction in JVMS 6.5.
            throw e;
        }
        catch (Throwable ex) {
            // Wrap anything else in BootstrapMethodError
            throw new BootstrapMethodError("bootstrap method initialization exception", ex);
        }
    }

    /** The JVM produces java.lang.Integer values to box
     *  CONSTANT_Integer boxes but does not intern them.
     *  Let's intern them.  This is slightly wrong for
     *  a {@code CONSTANT_Dynamic} which produces an
     *  un-interned integer (e.g., {@code new Integer(0)}).
     */
    private static Object maybeReBox(Object x) {
        if (x instanceof Integer) {
            int xi = (int) x;
            if (xi == (byte) xi)
                x = xi;  // must rebox; see JLS 5.1.7
        }
        return x;
    }

    private static void maybeReBoxElements(Object[] xa) {
        for (int i = 0; i < xa.length; i++) {
            xa[i] = maybeReBox(xa[i]);
        }
    }

    /** Canonical VM-aware implementation of BootstrapCallInfo.
     * Knows how to dig into the JVM for lazily resolved (pull-mode) constants.
     */
    private static final class VM_BSCI<T> extends BSCIWithCache<T> {
        private final int[] indexInfo;
        private final Class<?> caller;  // for index resolution only

        VM_BSCI(MethodHandle bsm, String name, T type,
                Lookup lookup, int[] indexInfo) {
            super(bsm, name, type, indexInfo[0]);
            if (!lookup.hasPrivateAccess())  //D.I.D.
                throw new AssertionError("bad Lookup object");
            this.caller = lookup.lookupClass();
            this.indexInfo = indexInfo;
            // scoop up all the easy stuff right away:
            prefetchIntoCache(0, size());
        }

        @Override Object fillCache(int i) {
            Object[] buf = { null };
            copyConstants(i, i+1, buf, 0);
            Object res = wrapNull(buf[0]);
            cache[i] = res;
            int next = i + 1;
            if (next < cache.length && cache[next] == null)
                maybePrefetchIntoCache(next, false);  // try to prefetch
            return res;
        }

        @Override public int copyConstants(int start, int end,
                                           Object[] buf, int pos) {
            int i = start, bufi = pos;
            while (i < end) {
                Object x = cache[i];
                if (x == null)  break;
                buf[bufi++] = unwrapNull(x);
                i++;
            }
            // give up at first null and grab the rest in one big block
            if (i >= end)  return i;
            Object[] temp = new Object[end - i];
            if (TRACE_METHOD_LINKAGE)
                System.out.println("resolving more BSM arguments: "+
                        Arrays.asList(caller.getSimpleName(), Arrays.toString(indexInfo), i, end));
            copyOutBootstrapArguments(caller, indexInfo,
                                      i, end, temp, 0,
                                      true, null);
            for (Object x : temp) {
                x = maybeReBox(x);
                buf[bufi++] = x;
                cache[i++] = wrapNull(x);
            }
            if (end < cache.length && cache[end] == null)
                maybePrefetchIntoCache(end, true);  // try to prefetch
            return i;
        }

        private static final int MIN_PF = 4;
        private void maybePrefetchIntoCache(int i, boolean bulk) {
            int len = cache.length;
            assert(0 <= i && i <= len);
            int pfLimit = i;
            if (bulk)  pfLimit += i;  // exponential prefetch expansion
            // try to prefetch at least MIN_PF elements
            if (pfLimit < i + MIN_PF)  pfLimit = i + MIN_PF;
            if (pfLimit > len || pfLimit < 0)  pfLimit = len;
            // stop prefetching where cache is more full than empty
            int empty = 0, nonEmpty = 0, lastEmpty = i;
            for (int j = i; j < pfLimit; j++) {
                if (cache[j] == null) {
                    empty++;
                    lastEmpty = j;
                } else {
                    nonEmpty++;
                    if (nonEmpty > empty) {
                        pfLimit = lastEmpty + 1;
                        break;
                    }
                    if (pfLimit < len)  pfLimit++;
                }
            }
            if (bulk && empty < MIN_PF && pfLimit < len)
                return;  // not worth the effort
            prefetchIntoCache(i, pfLimit);
        }

        private void prefetchIntoCache(int i, int pfLimit) {
            if (pfLimit <= i)  return;  // corner case
            Object[] temp = new Object[pfLimit - i];
            if (TRACE_METHOD_LINKAGE)
                System.out.println("prefetching BSM arguments: "+
                        Arrays.asList(caller.getSimpleName(), Arrays.toString(indexInfo), i, pfLimit));
            copyOutBootstrapArguments(caller, indexInfo,
                                      i, pfLimit, temp, 0,
                                      false, NOT_PRESENT);
            for (Object x : temp) {
                if (x != NOT_PRESENT && cache[i] == null) {
                    cache[i] = wrapNull(maybeReBox(x));
                }
                i++;
            }
        }
    }

    /*non-public*/ static final
    class Adapters {
        // skeleton for push-mode BSM which wraps a pull-mode BSM:
        static Object pushToBootstrapMethod(MethodHandle pullModeBSM,
                                            MethodHandles.Lookup lookup, String name, Object type,
                                            Object... arguments) throws Throwable {
            ConstantGroup cons = makeConstantGroup(Arrays.asList(arguments));
            BootstrapCallInfo<?> bsci = makeBootstrapCallInfo(pullModeBSM, name, type, cons);
            if (TRACE_METHOD_LINKAGE)
                System.out.println("pull-mode BSM gets pushed arguments from fake BSCI");
            return pullModeBSM.invoke(lookup, bsci);
        }

        // skeleton for pull-mode BSM which wraps a push-mode BSM:
        static Object pullFromBootstrapMethod(MethodHandle pushModeBSM,
                                              MethodHandles.Lookup lookup, BootstrapCallInfo<?> bsci)
                throws Throwable {
            int argc = bsci.size();
            Object arguments[] = new Object[3 + argc];
            arguments[0] = lookup;
            arguments[1] = bsci.invocationName();
            arguments[2] = bsci.invocationType();
            bsci.copyConstants(0, argc, arguments, 3);
            if (TRACE_METHOD_LINKAGE)
                System.out.println("pulled arguments from VM for push-mode BSM");
            return pushModeBSM.invokeWithArguments(arguments);
        }
        static final MethodHandle MH_pushToBootstrapMethod;
        static final MethodHandle MH_pullFromBootstrapMethod;
        static {
            final Class<?> THIS_CLASS = Adapters.class;
            try {
                MH_pushToBootstrapMethod = IMPL_LOOKUP
                    .findStatic(THIS_CLASS, "pushToBootstrapMethod",
                                MethodType.methodType(Object.class, MethodHandle.class,
                                        Lookup.class, String.class, Object.class, Object[].class));
                MH_pullFromBootstrapMethod = IMPL_LOOKUP
                    .findStatic(THIS_CLASS, "pullFromBootstrapMethod",
                                MethodType.methodType(Object.class, MethodHandle.class,
                                        Lookup.class, BootstrapCallInfo.class));
            } catch (Throwable ex) {
                throw new InternalError(ex);
            }
        }

        /** Given a push-mode BSM (taking one argument) convert it to a
         *  pull-mode BSM (taking N pre-resolved arguments).
         *  This method is used when, in fact, the JVM is passing up
         *  pre-resolved arguments, but the BSM is expecting lazy stuff.
         *  Or, when goToPushMode is true, do the reverse transform.
         *  (The two transforms are exactly inverse.)
         */
        static MethodHandle pushMePullYou(MethodHandle bsm, boolean goToPushMode) {
            if (TRACE_METHOD_LINKAGE)
                System.out.println("converting BSM to "+(goToPushMode ? "push mode" : "pull mode"));
            assert(isPullModeBSM(bsm) == goToPushMode);  //there must be a change
            if (goToPushMode) {
                return Adapters.MH_pushToBootstrapMethod.bindTo(bsm).withVarargs(true);
            } else {
                return Adapters.MH_pullFromBootstrapMethod.bindTo(bsm).withVarargs(false);
            }
        }
    }
}