/*

 * Copyright (c) 2019, 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.

 *

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.vm.ci.hotspot;

import java.io.ByteArrayOutputStream;

import java.io.DataOutputStream;

import java.io.IOException;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import java.util.Arrays;

import jdk.vm.ci.common.JVMCIError;

import jdk.vm.ci.meta.ResolvedJavaMethod;

import jdk.vm.ci.meta.ResolvedJavaType;

import jdk.vm.ci.meta.SpeculationLog.SpeculationReasonEncoding;

/**

 * Implements a {@link SpeculationReasonEncoding} that {@linkplain #getByteArray() produces} a byte

 * array. Data is added via a {@link DataOutputStream}. When producing the final byte array, if the

 * total length of data exceeds the length of a SHA-1 digest, then a SHA-1 digest of the data is

 * produced instead.

 */

final class HotSpotSpeculationEncoding extends ByteArrayOutputStream implements SpeculationReasonEncoding {

    private DataOutputStream dos = new DataOutputStream(this);

    private byte[] result;

    HotSpotSpeculationEncoding() {

        super(SHA1_LENGTH);

    }

    private void checkOpen() {

        if (result != null) {

            throw new IllegalArgumentException("Cannot update closed speculation encoding");

        }

    }

    private static final int NULL_METHOD = -1;

    private static final int NULL_TYPE = -2;

    private static final int NULL_STRING = -3;

    @Override

    public void addByte(int value) {

        checkOpen();

        try {

            dos.writeByte(value);

        } catch (IOException e) {

            throw new InternalError(e);

        }

    }

    @Override

    public void addShort(int value) {

        checkOpen();

        try {

            dos.writeShort(value);

        } catch (IOException e) {

            throw new InternalError(e);

        }

    }

    @Override

    public void addMethod(ResolvedJavaMethod method) {

        if (!addNull(method, NULL_METHOD)) {

            checkOpen();

            if (method instanceof HotSpotResolvedJavaMethodImpl) {

                try {

                    dos.writeLong(((HotSpotResolvedJavaMethodImpl) method).getMetaspaceMethod());

                } catch (IOException e) {

                    throw new InternalError(e);

                }

            } else {

                throw new IllegalArgumentException("Cannot encode unsupported type " + method.getClass().getName() + ": " + method.format("%H.%n(%p)"));

            }

        }

    }

    @Override

    public void addType(ResolvedJavaType type) {

        if (!addNull(type, NULL_TYPE)) {

            checkOpen();

            if (type instanceof HotSpotResolvedObjectTypeImpl) {

                try {

                    dos.writeLong(((HotSpotResolvedObjectTypeImpl) type).getMetaspaceKlass());

                } catch (IOException e) {

                    throw new InternalError(e);

                }

            } else {

                throw new IllegalArgumentException("Cannot encode unsupported type " + type.getClass().getName() + ": " + type.toClassName());

            }

        }

    }

    @Override

    public void addString(String value) {

        if (!addNull(value, NULL_STRING)) {

            checkOpen();

            try {

                dos.writeChars(value);

            } catch (IOException e) {

                throw new InternalError(e);

            }

        }

    }

    @Override

    public void addInt(int value) {

        checkOpen();

        try {

            dos.writeInt(value);

        } catch (IOException e) {

            throw new InternalError(e);

        }

    }

    @Override

    public void addLong(long value) {

        checkOpen();

        try {

            dos.writeLong(value);

        } catch (IOException e) {

            throw new InternalError(e);

        }

    }

    private boolean addNull(Object o, int nullValue) {

        if (o == null) {

            addInt(nullValue);

            return true;

        }

        return false;

    }

    /**

     * Prototype SHA1 digest that is cloned before use.

     */

    private static final MessageDigest SHA1 = getSHA1();

    private static final int SHA1_LENGTH = SHA1.getDigestLength();

    private static MessageDigest getSHA1() {

        try {

            MessageDigest sha1 = MessageDigest.getInstance("SHA-1");

            sha1.clone();

            return sha1;

        } catch (CloneNotSupportedException | NoSuchAlgorithmException e) {

            // Should never happen given that SHA-1 is mandated in a

            // compliant Java platform implementation.

            throw new JVMCIError("Expect a cloneable implementation of a SHA-1 message digest to be available", e);

        }

    }

    /**

     * Gets the final encoded byte array and closes this encoding such that any further attempts to

     * update it result in an {@link IllegalArgumentException}.

     */

    byte[] getByteArray() {

        if (result == null) {

            if (count > SHA1_LENGTH) {

                try {

                    MessageDigest md = (MessageDigest) SHA1.clone();

                    md.update(buf, 0, count);

                    result = md.digest();

                } catch (CloneNotSupportedException e) {

                    throw new InternalError(e);

                }

            } else {

                if (buf.length == count) {

                    // No need to copy the byte array

                    return buf;

                }

                result = Arrays.copyOf(buf, count);

            }

            dos = null;

        }

        return result;

    }

}