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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.vertexium.inmemory.security;

/**
 * A sequence of bytes.
 */
abstract class ByteSequence implements Comparable {

    /**
     * Gets a byte within this sequence.
     *
     * @param i index into sequence
     * @return byte
     * @throws IllegalArgumentException if i is out of range
     */
    public abstract byte byteAt(int i);

    /**
     * Gets the length of this sequence.
     *
     * @return sequence length
     */
    public abstract int length();

    /**
     * Returns a portion of this sequence.
     *
     * @param start index of subsequence start (inclusive)
     * @param end   index of subsequence end (exclusive)
     */
    public abstract ByteSequence subSequence(int start, int end);

    /**
     * Returns a byte array containing the bytes in this sequence. This method
     * may copy the sequence data or may return a backing byte array directly.
     *
     * @return byte array
     */
    public abstract byte[] toArray();

    /**
     * Determines whether this sequence is backed by a byte array.
     *
     * @return true if sequence is backed by a byte array
     */
    public abstract boolean isBackedByArray();

    /**
     * Gets the backing byte array for this sequence.
     *
     * @return byte array
     */
    public abstract byte[] getBackingArray();

    /**
     * Gets the offset for this sequence. This value represents the starting
     * point for the sequence in the backing array, if there is one.
     *
     * @return offset (inclusive)
     */
    public abstract int offset();

    /**
     * Compares the two given byte sequences, byte by byte, returning a negative,
     * zero, or positive result if the first sequence is less than, equal to, or
     * greater than the second. The comparison is performed starting with the
     * first byte of each sequence, and proceeds until a pair of bytes differs,
     * or one sequence runs out of byte (is shorter). A shorter sequence is
     * considered less than a longer one.
     *
     * @param bs1 first byte sequence to compare
     * @param bs2 second byte sequence to compare
     * @return comparison result
     */
    public static int compareBytes(ByteSequence bs1, ByteSequence bs2) {

        int minLen = Math.min(bs1.length(), bs2.length());

        for (int i = 0; i < minLen; i++) {
            int a = (bs1.byteAt(i) & 0xff);
            int b = (bs2.byteAt(i) & 0xff);

            if (a != b) {
                return a - b;
            }
        }

        return bs1.length() - bs2.length();
    }

    /**
     * Compares this byte sequence to another.
     *
     * @param obs byte sequence to compare
     * @return comparison result
     * @see #compareBytes(ByteSequence, ByteSequence)
     */
    public int compareTo(ByteSequence obs) {
        if (isBackedByArray() && obs.isBackedByArray()) {
            return WritableComparator.compareBytes(getBackingArray(), offset(), length(), obs.getBackingArray(), obs.offset(), obs.length());
        }

        return compareBytes(this, obs);
    }

    @Override
    public boolean equals(Object o) {
        if (o instanceof ByteSequence) {
            ByteSequence obs = (ByteSequence) o;

            if (this == o)
                return true;

            if (length() != obs.length())
                return false;

            return compareTo(obs) == 0;
        }

        return false;

    }

    @Override
    public int hashCode() {
        int hash = 1;
        if (isBackedByArray()) {
            byte[] data = getBackingArray();
            int end = offset() + length();
            for (int i = offset(); i < end; i++)
                hash = (31 * hash) + data[i];
        } else {
            for (int i = 0; i < length(); i++)
                hash = (31 * hash) + byteAt(i);
        }
        return hash;
    }

}