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/*--------------------------------------------------------------------------
 *  Copyright 2004 Taro L. Saito
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *--------------------------------------------------------------------------*/
//--------------------------------------
// XerialJ
//
// VariableLengthInteger.java
// Since: 2005/07/21 14:59:45
//
// $URL$
// $Author$
//--------------------------------------
package org.xerial.util;

import java.io.ByteArrayInputStream;
import java.math.BigInteger;
import java.util.Vector;

import org.xerial.core.XerialErrorCode;
import org.xerial.core.XerialException;
import org.xerial.util.io.Buffer;
import org.xerial.util.io.BufferWriter;

/**
 * Variable length number representation. When the most significant bit (MSB) of
 * a byte is 0, it means the termination of the value, when the MSB of a byte is
 * 1, its following bytes must be read to compute the value.
 * 
 * 0XXXXXXX : [0, 127 (= M1 - 1)] 1XXXXXXX 0XXXXXXX : [M1, M1 + 127 * 2^7 + 127
 * (= M2-1)] 1XXXXXXX 1XXXXXXX 0XXXXXXX : [M2, M2 + 127 * 2^14 + 127 * 2^7 +
 * 127]
 * 
 * [0, 0 + (2 ^ 7 - 1) = 127] [128, 128 + (2^14 - 1) = 16511] [16512, 16512 +
 * (2^21 - 1) = 2113663]
 * 
 * @author leo
 * 
 */
public class VariableLengthInteger {
    static private int[] upperBoundByByteSize;
    static {
        Vector upperBoundArray = new Vector();
        BigInteger previousMaximum = BigInteger.ZERO;
        BigInteger intMax = BigInteger.valueOf(Integer.MAX_VALUE);

        int byteSize = 1;
        BigInteger valueRange = BigInteger.ZERO;
        while (previousMaximum.compareTo(intMax) < 0) {
            valueRange = BigInteger.ZERO.setBit(byteSize++ * 7);
            previousMaximum = previousMaximum.add(valueRange);
            if (previousMaximum.compareTo(intMax) > 0)
                break;
            upperBoundArray.add(previousMaximum.subtract(BigInteger.ONE).intValue());
        }

        upperBoundByByteSize = new int[upperBoundArray.size()];
        int i = 0;
        for (int val : upperBoundArray) {
            upperBoundByByteSize[i++] = val;
        }
    }

    byte[] _binaryRepresentation = null;

    public VariableLengthInteger(int value) {
        translate(value);
    }

    public VariableLengthInteger(byte[] byteArray, int offset) throws XerialException {
        translate(byteArray, offset);
    }

    public byte[] getByte() {
        assert _binaryRepresentation != null;
        return _binaryRepresentation;
    }

    public int size() {
        assert _binaryRepresentation != null;
        return _binaryRepresentation.length;
    }

    public int intValue() {
        assert _binaryRepresentation != null;
        int value = 0;
        for (int i = 0; i < _binaryRepresentation.length; i++) {
            value <<= 7;
            value |= _binaryRepresentation[i] & 0x7F;
        }
        if (_binaryRepresentation.length > 1)
            value += upperBoundByByteSize[_binaryRepresentation.length - 2] + 1;
        return value;
    }

    private void translate(int value) {
        int byteSize;
        for (byteSize = 1; byteSize <= upperBoundByByteSize.length; byteSize++) {
            if (value <= upperBoundByByteSize[byteSize - 1])
                break;
        }

        if (byteSize > 1)
            value -= upperBoundByByteSize[byteSize - 2] + 1; // subtract offset

        _binaryRepresentation = new byte[byteSize];
        int mask = 0x7F << ((byteSize - 1) * 7);
        for (int i = 0; i < byteSize; i++) {
            _binaryRepresentation[i] = (byte) ((value & mask) >> ((byteSize - (i + 1)) * 7));
            mask >>= 7;
        }
        for (int i = 0; i < _binaryRepresentation.length - 1; i++) {
            _binaryRepresentation[i] |= 0x80;
        }

    }

    public static int byteSize(byte[] buffer, int offset) throws XerialException {
        int byteLength = 1;
        int index = offset;
        while ((buffer[index++] & 0x80) != 0) {
            byteLength++;
            if (byteLength > upperBoundByByteSize.length) {
                throw new XerialException(XerialErrorCode.InvalidFormat,
                        "cannot read the variable length integer whose bite size is larger than "
                                + upperBoundByByteSize.length);
            }
        }
        return byteLength;

    }

    /**
     * Gets the byte size of the value as an variable length integer
     * 
     * @param value
     * @return
     */
    public static int byteSize(int value) {
        int byteSize;
        for (byteSize = 1; byteSize <= upperBoundByByteSize.length; byteSize++) {
            if (value <= upperBoundByByteSize[byteSize - 1])
                break;
        }
        return byteSize;
    }

    public static int readFrom(byte[] buffer, int offset) throws XerialException {
        int value = 0;
        int byteLength = byteSize(buffer, offset);
        if (byteLength > Buffer.INT_SIZE) {
            if (!(byteLength == (Buffer.INT_SIZE + 1) && (buffer[offset] > 0x87))) // 1000 0111
                throw new XerialException(XerialErrorCode.INVALID_INPUT,
                        "value larger than 2^31-1 cannot be read");
        }

        for (int i = 0; i < byteLength; i++) {
            value <<= 7;
            value |= buffer[offset + i] & 0x7F;
        }

        return value;
    }

    public static VariableLengthInteger readFrom(ByteArrayInputStream buffer)
            throws XerialException {
        byte[] byteArray = new byte[upperBoundByByteSize.length];
        int size = 0, b;
        while (((b = buffer.read()) & 0x80) != 0) {
            byteArray[size++] = (byte) b;
        }
        return new VariableLengthInteger(byteArray, 0);
    }

    private void translate(byte[] byteArray, int offset) throws XerialException {
        int index = offset;
        while (index < byteArray.length) {
            if ((byteArray[index] & 0x80) == 0) {
                int byteSize = index - offset + 1;
                _binaryRepresentation = new byte[byteSize];
                for (int i = 0; i < byteSize; i++)
                    _binaryRepresentation[i] = byteArray[offset + i];
                return;
            }
            index++;
        }
        throw new XerialException(XerialErrorCode.InvalidFormat, "invalid code");
    }

    public int writeTo(BufferWriter writer) {
        for (int i = 0; i < _binaryRepresentation.length; i++) {
            writer.writeByte(_binaryRepresentation[i]);
        }
        return _binaryRepresentation.length;
    }

}