/*

 * Copyright (c) 2015, 2018, 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

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

 * questions.

 */

import java.nio.ByteBuffer;

import java.util.Arrays;

final class IntegerWriter {

    private static final int NEW                = 0;

    private static final int CONFIGURED         = 1;

    private static final int FIRST_BYTE_WRITTEN = 2;

    private static final int DONE               = 4;

    private int state = NEW;

    private int payload;

    private int N;

    private int value;

    //

    //      0   1   2   3   4   5   6   7

    //    +---+---+---+---+---+---+---+---+

    //    |   |   |   |   |   |   |   |   |

    //    +---+---+---+-------------------+

    //    |<--------->|<----------------->|

    //       payload           N=5

    //

    // payload is the contents of the left-hand side part of the octet;

    //         it is truncated to fit into 8-N bits, where 1 <= N <= 8;

    //

    public IntegerWriter configure(int value, int N, int payload) {

        if (state != NEW) {

            throw new IllegalStateException("Already configured");

        }

        if (value < 0) {

            throw new IllegalArgumentException("value >= 0: value=" + value);

        }

        checkPrefix(N);

        this.value = value;

        this.N = N;

        this.payload = payload & 0xFF & (0xFFFFFFFF << N);

        state = CONFIGURED;

        return this;

    }

    public boolean write(ByteBuffer output) {

        if (state == NEW) {

            throw new IllegalStateException("Configure first");

        }

        if (state == DONE) {

            return true;

        }

        if (!output.hasRemaining()) {

            return false;

        }

        if (state == CONFIGURED) {

            int max = (2 << (N - 1)) - 1;

            if (value < max) {

                output.put((byte) (payload | value));

                state = DONE;

                return true;

            }

            output.put((byte) (payload | max));

            value -= max;

            state = FIRST_BYTE_WRITTEN;

        }

        if (state == FIRST_BYTE_WRITTEN) {

            while (value >= 128 && output.hasRemaining()) {

                output.put((byte) (value % 128 + 128));

                value /= 128;

            }

            if (!output.hasRemaining()) {

                return false;

            }

            output.put((byte) value);

            state = DONE;

            return true;

        }

        throw new InternalError(Arrays.toString(

                new Object[]{state, payload, N, value}));

    }

    private static void checkPrefix(int N) {

        if (N < 1 || N > 8) {

            throw new IllegalArgumentException("1 <= N <= 8: N= " + N);

        }

    }

    public IntegerWriter reset() {

        state = NEW;

        return this;

    }

}