/*

 * Copyright (c) 2016, 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  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  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  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 java.net.http;

import java.nio.ByteBuffer;

import static java.lang.String.format;

import static java.net.http.WSFrame.Opcode.ofCode;

import static java.net.http.WSUtils.dump;

/*

 * A collection of utilities for reading, writing, and masking frames.

 */

final class WSFrame {

    private WSFrame() { }

    static final int MAX_HEADER_SIZE_BYTES = 2 + 8 + 4;

    enum Opcode {

        CONTINUATION   (0x0),

        TEXT           (0x1),

        BINARY         (0x2),

        NON_CONTROL_0x3(0x3),

        NON_CONTROL_0x4(0x4),

        NON_CONTROL_0x5(0x5),

        NON_CONTROL_0x6(0x6),

        NON_CONTROL_0x7(0x7),

        CLOSE          (0x8),

        PING           (0x9),

        PONG           (0xA),

        CONTROL_0xB    (0xB),

        CONTROL_0xC    (0xC),

        CONTROL_0xD    (0xD),

        CONTROL_0xE    (0xE),

        CONTROL_0xF    (0xF);

        private static final Opcode[] opcodes;

        static {

            Opcode[] values = values();

            opcodes = new Opcode[values.length];

            for (Opcode c : values) {

                assert opcodes[c.code] == null

                        : WSUtils.dump(c, c.code, opcodes[c.code]);

                opcodes[c.code] = c;

            }

        }

        private final byte code;

        private final char shiftedCode;

        private final String description;

        Opcode(int code) {

            this.code = (byte) code;

            this.shiftedCode = (char) (code << 8);

            this.description = format("%x (%s)", code, name());

        }

        boolean isControl() {

            return (code & 0x8) != 0;

        }

        static Opcode ofCode(int code) {

            return opcodes[code & 0xF];

        }

        @Override

        public String toString() {

            return description;

        }

    }

    /*

     * A utility to mask payload data.

     */

    static final class Masker {

        private final ByteBuffer acc = ByteBuffer.allocate(8);

        private final int[] maskBytes = new int[4];

        private int offset;

        private long maskLong;

        /*

         * Sets up the mask.

         */

        Masker mask(int value) {

            acc.clear().putInt(value).putInt(value).flip();

            for (int i = 0; i < maskBytes.length; i++) {

                maskBytes[i] = acc.get(i);

            }

            offset = 0;

            maskLong = acc.getLong(0);

            return this;

        }

        /*

         * Reads as many bytes as possible from the given input buffer, writing

         * the resulting masked bytes to the given output buffer.

         *

         * src.remaining() <= dst.remaining() // TODO: do we need this restriction?

         * 'src' and 'dst' can be the same ByteBuffer

         */

        Masker applyMask(ByteBuffer src, ByteBuffer dst) {

            if (src.remaining() > dst.remaining()) {

                throw new IllegalArgumentException(dump(src, dst));

            }

            begin(src, dst);

            loop(src, dst);

            end(src, dst);

            return this;

        }

        // Applying the remaining of the mask (strictly not more than 3 bytes)

        // byte-wise

        private void begin(ByteBuffer src, ByteBuffer dst) {

            if (offset > 0) {

                for (int i = src.position(), j = dst.position();

                     offset < 4 && i <= src.limit() - 1 && j <= dst.limit() - 1;

                     i++, j++, offset++) {

                    dst.put(j, (byte) (src.get(i) ^ maskBytes[offset]));

                    dst.position(j + 1);

                    src.position(i + 1);

                }

                offset &= 3;

            }

        }

        private void loop(ByteBuffer src, ByteBuffer dst) {

            int i = src.position();

            int j = dst.position();

            final int srcLim = src.limit() - 8;

            final int dstLim = dst.limit() - 8;

            for (; i <= srcLim && j <= dstLim; i += 8, j += 8) {

                dst.putLong(j, (src.getLong(i) ^ maskLong));

            }

            if (i > src.limit()) {

                src.position(i - 8);

            } else {

                src.position(i);

            }

            if (j > dst.limit()) {

                dst.position(j - 8);

            } else {

                dst.position(j);

            }

        }

        // Applying the mask to the remaining bytes byte-wise (don't make any

        // assumptions on how many, hopefully not more than 7 for 64bit arch)

        private void end(ByteBuffer src, ByteBuffer dst) {

            for (int i = src.position(), j = dst.position();

                 i <= src.limit() - 1 && j <= dst.limit() - 1;

                 i++, j++, offset = (offset + 1) & 3) { // offset cycle through 0..3

                dst.put(j, (byte) (src.get(i) ^ maskBytes[offset]));

                src.position(i + 1);

                dst.position(j + 1);

            }

        }

    }

    /*

     * A builder of frame headers, capable of writing to a given buffer.

     *

     * The builder does not enforce any protocol-level rules, it simply writes

     * a header structure to the buffer. The order of calls to intermediate

     * methods is not significant.

     */

    static final class HeaderBuilder {

        private char firstChar;

        private long payloadLen;

        private int maskingKey;

        private boolean mask;

        HeaderBuilder fin(boolean value) {

            if (value) {

                firstChar |=  0b10000000_00000000;

            } else {

                firstChar &= ~0b10000000_00000000;

            }

            return this;

        }

        HeaderBuilder rsv1(boolean value) {

            if (value) {

                firstChar |=  0b01000000_00000000;

            } else {

                firstChar &= ~0b01000000_00000000;

            }

            return this;

        }

        HeaderBuilder rsv2(boolean value) {

            if (value) {

                firstChar |=  0b00100000_00000000;

            } else {

                firstChar &= ~0b00100000_00000000;

            }

            return this;

        }

        HeaderBuilder rsv3(boolean value) {

            if (value) {

                firstChar |=  0b00010000_00000000;

            } else {

                firstChar &= ~0b00010000_00000000;

            }

            return this;

        }

        HeaderBuilder opcode(Opcode value) {

            firstChar = (char) ((firstChar & 0xF0FF) | value.shiftedCode);

            return this;

        }

        HeaderBuilder payloadLen(long value) {

            payloadLen = value;

            firstChar &= 0b11111111_10000000; // Clear previous payload length leftovers

            if (payloadLen < 126) {

                firstChar |= payloadLen;

            } else if (payloadLen < 65535) {

                firstChar |= 126;

            } else {

                firstChar |= 127;

            }

            return this;

        }

        HeaderBuilder mask(int value) {

            firstChar |= 0b00000000_10000000;

            maskingKey = value;

            mask = true;

            return this;

        }

        HeaderBuilder noMask() {

            firstChar &= ~0b00000000_10000000;

            mask = false;

            return this;

        }

        /*

         * Writes the header to the given buffer.

         *

         * The buffer must have at least MAX_HEADER_SIZE_BYTES remaining. The

         * buffer's position is incremented by the number of bytes written.

         */

        void build(ByteBuffer buffer) {

            buffer.putChar(firstChar);

            if (payloadLen >= 126) {

                if (payloadLen < 65535) {

                    buffer.putChar((char) payloadLen);

                } else {

                    buffer.putLong(payloadLen);

                }

            }

            if (mask) {

                buffer.putInt(maskingKey);

            }

        }

    }

    /*

     * A consumer of frame parts.

     *

     * Guaranteed to be called in the following order by the Frame.Reader:

     *

     *     fin rsv1 rsv2 rsv3 opcode mask payloadLength maskingKey? payloadData+ endFrame

     */

    interface Consumer {

        void fin(boolean value);

        void rsv1(boolean value);

        void rsv2(boolean value);

        void rsv3(boolean value);

        void opcode(Opcode value);

        void mask(boolean value);

        void payloadLen(long value);

        void maskingKey(int value);

        /*

         * Called when a part of the payload is ready to be consumed.

         *

         * Though may not yield a complete payload in a single invocation, i.e.

         *

         *     data.remaining() < payloadLen

         *

         * the sum of `data.remaining()` passed to all invocations of this

         * method will be equal to 'payloadLen', reported in

         * `void payloadLen(long value)`

         *

         * No unmasking is done.

         */

        void payloadData(WSShared<ByteBuffer> data, boolean isLast);

        void endFrame(); // TODO: remove (payloadData(isLast=true)) should be enough

    }

    /*

     * A Reader of Frames.

     *

     * No protocol-level rules are enforced, only frame structure.

     */

    static final class Reader {

        private static final int AWAITING_FIRST_BYTE  =  1;

        private static final int AWAITING_SECOND_BYTE =  2;

        private static final int READING_16_LENGTH    =  4;

        private static final int READING_64_LENGTH    =  8;

        private static final int READING_MASK         = 16;

        private static final int READING_PAYLOAD      = 32;

        // A private buffer used to simplify multi-byte integers reading

        private final ByteBuffer accumulator = ByteBuffer.allocate(8);

        private int state = AWAITING_FIRST_BYTE;

        private boolean mask;

        private long payloadLength;

        /*

         * Reads at most one frame from the given buffer invoking the consumer's

         * methods corresponding to the frame elements found.

         *

         * As much of the frame's payload, if any, is read. The buffers position

         * is updated to reflect the number of bytes read.

         *

         * Throws WSProtocolException if the frame is malformed.

         */

        void readFrame(WSShared<ByteBuffer> shared, Consumer consumer) {

            ByteBuffer input = shared.buffer();

            loop:

            while (true) {

                byte b;

                switch (state) {

                    case AWAITING_FIRST_BYTE:

                        if (!input.hasRemaining()) {

                            break loop;

                        }

                        b = input.get();

                        consumer.fin( (b & 0b10000000) != 0);

                        consumer.rsv1((b & 0b01000000) != 0);

                        consumer.rsv2((b & 0b00100000) != 0);

                        consumer.rsv3((b & 0b00010000) != 0);

                        consumer.opcode(ofCode(b));

                        state = AWAITING_SECOND_BYTE;

                        continue loop;

                    case AWAITING_SECOND_BYTE:

                        if (!input.hasRemaining()) {

                            break loop;

                        }

                        b = input.get();

                        consumer.mask(mask = (b & 0b10000000) != 0);

                        byte p1 = (byte) (b & 0b01111111);

                        if (p1 < 126) {

                            assert p1 >= 0 : p1;

                            consumer.payloadLen(payloadLength = p1);

                            state = mask ? READING_MASK : READING_PAYLOAD;

                        } else if (p1 < 127) {

                            state = READING_16_LENGTH;

                        } else {

                            state = READING_64_LENGTH;

                        }

                        continue loop;

                    case READING_16_LENGTH:

                        if (!input.hasRemaining()) {

                            break loop;

                        }

                        b = input.get();

                        if (accumulator.put(b).position() < 2) {

                            continue loop;

                        }

                        payloadLength = accumulator.flip().getChar();

                        if (payloadLength < 126) {

                            throw notMinimalEncoding(payloadLength, 2);

                        }

                        consumer.payloadLen(payloadLength);

                        accumulator.clear();

                        state = mask ? READING_MASK : READING_PAYLOAD;

                        continue loop;

                    case READING_64_LENGTH:

                        if (!input.hasRemaining()) {

                            break loop;

                        }

                        b = input.get();

                        if (accumulator.put(b).position() < 8) {

                            continue loop;

                        }

                        payloadLength = accumulator.flip().getLong();

                        if (payloadLength < 0) {

                            throw negativePayload(payloadLength);

                        } else if (payloadLength < 65535) {

                            throw notMinimalEncoding(payloadLength, 8);

                        }

                        consumer.payloadLen(payloadLength);

                        accumulator.clear();

                        state = mask ? READING_MASK : READING_PAYLOAD;

                        continue loop;

                    case READING_MASK:

                        if (!input.hasRemaining()) {

                            break loop;

                        }

                        b = input.get();

                        if (accumulator.put(b).position() != 4) {

                            continue loop;

                        }

                        consumer.maskingKey(accumulator.flip().getInt());

                        accumulator.clear();

                        state = READING_PAYLOAD;

                        continue loop;

                    case READING_PAYLOAD:

                        // This state does not require any bytes to be available

                        // in the input buffer in order to proceed

                        boolean fullyRead;

                        int limit;

                        if (payloadLength <= input.remaining()) {

                            limit = input.position() + (int) payloadLength;

                            payloadLength = 0;

                            fullyRead = true;

                        } else {

                            limit = input.limit();

                            payloadLength -= input.remaining();

                            fullyRead = false;

                        }

                        // FIXME: consider a case where payloadLen != 0,

                        // but input.remaining() == 0

                        //

                        // There shouldn't be an invocation of payloadData with

                        // an empty buffer, as it would be an artifact of

                        // reading

                        consumer.payloadData(shared.share(input.position(), limit), fullyRead);

                        // Update the position manually, since reading the

                        // payload doesn't advance buffer's position

                        input.position(limit);

                        if (fullyRead) {

                            consumer.endFrame();

                            state = AWAITING_FIRST_BYTE;

                        }

                        break loop;

                    default:

                        throw new InternalError(String.valueOf(state));

                }

            }

        }

        private static WSProtocolException negativePayload(long payloadLength) {

            return new WSProtocolException

                    ("5.2.", format("Negative 64-bit payload length %s", payloadLength));

        }

        private static WSProtocolException notMinimalEncoding(long payloadLength, int numBytes) {

            return new WSProtocolException

                    ("5.2.", format("Payload length (%s) is not encoded with minimal number (%s) of bytes",

                            payloadLength, numBytes));

        }

    }

}