/**
 * The MurmurHash3 algorithm was created by Austin Appleby and placed in the public domain.
 * This java port was authored by Yonik Seeley and also placed into the public domain.
 * The author hereby disclaims copyright to this source code.
 * <p>
 * This produces exactly the same hash values as the final C++
 * version of MurmurHash3 and is thus suitable for producing the same hash values across
 * platforms.
 * <p>
 * The 32 bit x86 version of this hash should be the fastest variant for relatively short keys like ids.
 * murmurhash3_x64_128 is a good choice for longer strings or if you need more than 32 bits of hash.
 * <p>
 * Note - The x86 and x64 versions do _not_ produce the same results, as the
 * algorithms are optimized for their respective platforms.
 * <p>
 * See http://github.com/yonik/java_util for future updates to this file.
 */
public final class MurmurHash3 {

    /**
     * 128 bits of state
     */
    public static final class LongPair {
        public long val1;
        public long val2;
    }

    public static final int fmix32(int h) {
        h ^= h >>> 16;
        h *= 0x85ebca6b;
        h ^= h >>> 13;
        h *= 0xc2b2ae35;
        h ^= h >>> 16;
        return h;
    }

    public static final long fmix64(long k) {
        k ^= k >>> 33;
        k *= 0xff51afd7ed558ccdL;
        k ^= k >>> 33;
        k *= 0xc4ceb9fe1a85ec53L;
        k ^= k >>> 33;
        return k;
    }

    /**
     * Gets a long from a byte buffer in little endian byte order.
     */
    public static final long getLongLittleEndian(byte[] buf, int offset) {
        return ((long) buf[offset + 7] << 56)   // no mask needed
                | ((buf[offset + 6] & 0xffL) << 48)
                | ((buf[offset + 5] & 0xffL) << 40)
                | ((buf[offset + 4] & 0xffL) << 32)
                | ((buf[offset + 3] & 0xffL) << 24)
                | ((buf[offset + 2] & 0xffL) << 16)
                | ((buf[offset + 1] & 0xffL) << 8)
                | ((buf[offset] & 0xffL));        // no shift needed
    }


    /**
     * Returns the MurmurHash3_x86_32 hash of the UTF-8 bytes of the String without actually encoding
     * the string to a temporary buffer.  This is more than 2x faster than hashing the result
     * of String.getBytes().
     */
    public static long murmurhash3_x86_32(CharSequence data, int seed) {
        final int c1 = 0xcc9e2d51;
        final int c2 = 0x1b873593;

        int h1 = seed;

        int offset = 0;
        int len = data.length();
        int pos = offset;
        int end = offset + len;
        int k1 = 0;
        int k2 = 0;
        int shift = 0;
        int bits = 0;
        int nBytes = 0;   // length in UTF8 bytes


        while (pos < end) {
            int code = data.charAt(pos++);
            if (code < 0x80) {
                k2 = code;
                bits = 8;

            } else if (code < 0x800) {
                k2 = (0xC0 | (code >> 6))
                        | ((0x80 | (code & 0x3F)) << 8);
                bits = 16;
            } else if (code < 0xD800 || code > 0xDFFF || pos >= end) {
                // we check for pos>=end to encode an unpaired surrogate as 3 bytes.
                k2 = (0xE0 | (code >> 12))
                        | ((0x80 | ((code >> 6) & 0x3F)) << 8)
                        | ((0x80 | (code & 0x3F)) << 16);
                bits = 24;
            } else {
                // surrogate pair
                // int utf32 = pos < end ? (int) data.charAt(pos++) : 0;
                int utf32 = (int) data.charAt(pos++);
                utf32 = ((code - 0xD7C0) << 10) + (utf32 & 0x3FF);
                k2 = (0xff & (0xF0 | (utf32 >> 18)))
                        | ((0x80 | ((utf32 >> 12) & 0x3F))) << 8
                        | ((0x80 | ((utf32 >> 6) & 0x3F))) << 16
                        | (0x80 | (utf32 & 0x3F)) << 24;
                bits = 32;
            }


            k1 |= k2 << shift;

            // int used_bits = 32 - shift;  // how many bits of k2 were used in k1.
            // int unused_bits = bits - used_bits; //  (bits-(32-shift)) == bits+shift-32  == bits-newshift

            shift += bits;
            if (shift >= 32) {
                // mix after we have a complete word

                k1 *= c1;
                k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
                k1 *= c2;

                h1 ^= k1;
                h1 = (h1 << 13) | (h1 >>> 19);  // ROTL32(h1,13);
                h1 = h1 * 5 + 0xe6546b64;

                shift -= 32;
                // unfortunately, java won't let you shift 32 bits off, so we need to check for 0
                if (shift != 0) {
                    k1 = k2 >>> (bits - shift);   // bits used == bits - newshift
                } else {
                    k1 = 0;
                }
                nBytes += 4;
            }

        } // inner

        // handle tail
        if (shift > 0) {
            nBytes += shift >> 3;
            k1 *= c1;
            k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
            k1 *= c2;
            h1 ^= k1;
        }

        // finalization
        h1 ^= nBytes;

        // fmix(h1);
        h1 ^= h1 >>> 16;
        h1 *= 0x85ebca6b;
        h1 ^= h1 >>> 13;
        h1 *= 0xc2b2ae35;
        h1 ^= h1 >>> 16;

        return h1 & 0xFFFFFFFFL;
    }

    // The following set of methods and constants are borrowed from:
    // `This method is borrowed from `org.apache.commons.codec.digest.MurmurHash3`

    // Constants for 128-bit variant
    private static final long C1 = 0x87c37b91114253d5L;
    private static final long C2 = 0x4cf5ad432745937fL;
    private static final int R1 = 31;
    private static final int R2 = 27;
    private static final int R3 = 33;
    private static final int M = 5;
    private static final int N1 = 0x52dce729;
    private static final int N2 = 0x38495ab5;

    /**
     * Gets the little-endian long from 8 bytes starting at the specified index.
     *
     * @param data The data
     * @param index The index
     * @return The little-endian long
     */
    private static long getLittleEndianLong(final byte[] data, final int index) {
        return (((long) data[index    ] & 0xff)      ) |
                (((long) data[index + 1] & 0xff) <<  8) |
                (((long) data[index + 2] & 0xff) << 16) |
                (((long) data[index + 3] & 0xff) << 24) |
                (((long) data[index + 4] & 0xff) << 32) |
                (((long) data[index + 5] & 0xff) << 40) |
                (((long) data[index + 6] & 0xff) << 48) |
                (((long) data[index + 7] & 0xff) << 56);
    }

    public static long[] hash128x64(final byte[] data) {
        return hash128x64(data, 0, data.length, 0);
    }

    /**
     * Generates 128-bit hash from the byte array with the given offset, length and seed.
     *
     * <p>This is an implementation of the 128-bit hash function {@code MurmurHash3_x64_128}
     * from from Austin Applyby's original MurmurHash3 {@code c++} code in SMHasher.</p>
     *
     * @param data The input byte array
     * @param offset The first element of array
     * @param length The length of array
     * @param seed The initial seed value
     * @return The 128-bit hash (2 longs)
     */
    public static long[] hash128x64(final byte[] data, final int offset, final int length, final long seed) {
        long h1 = seed;
        long h2 = seed;
        final int nblocks = length >> 4;

        // body
        for (int i = 0; i < nblocks; i++) {
            final int index = offset + (i << 4);
            long k1 = getLittleEndianLong(data, index);
            long k2 = getLittleEndianLong(data, index + 8);

            // mix functions for k1
            k1 *= C1;
            k1 = Long.rotateLeft(k1, R1);
            k1 *= C2;
            h1 ^= k1;
            h1 = Long.rotateLeft(h1, R2);
            h1 += h2;
            h1 = h1 * M + N1;

            // mix functions for k2
            k2 *= C2;
            k2 = Long.rotateLeft(k2, R3);
            k2 *= C1;
            h2 ^= k2;
            h2 = Long.rotateLeft(h2, R1);
            h2 += h1;
            h2 = h2 * M + N2;
        }

        // tail
        long k1 = 0;
        long k2 = 0;
        final int index = offset + (nblocks << 4);
        switch (offset + length - index) {
            case 15:
                k2 ^= ((long) data[index + 14] & 0xff) << 48;
            case 14:
                k2 ^= ((long) data[index + 13] & 0xff) << 40;
            case 13:
                k2 ^= ((long) data[index + 12] & 0xff) << 32;
            case 12:
                k2 ^= ((long) data[index + 11] & 0xff) << 24;
            case 11:
                k2 ^= ((long) data[index + 10] & 0xff) << 16;
            case 10:
                k2 ^= ((long) data[index + 9] & 0xff) << 8;
            case 9:
                k2 ^= data[index + 8] & 0xff;
                k2 *= C2;
                k2 = Long.rotateLeft(k2, R3);
                k2 *= C1;
                h2 ^= k2;

            case 8:
                k1 ^= ((long) data[index + 7] & 0xff) << 56;
            case 7:
                k1 ^= ((long) data[index + 6] & 0xff) << 48;
            case 6:
                k1 ^= ((long) data[index + 5] & 0xff) << 40;
            case 5:
                k1 ^= ((long) data[index + 4] & 0xff) << 32;
            case 4:
                k1 ^= ((long) data[index + 3] & 0xff) << 24;
            case 3:
                k1 ^= ((long) data[index + 2] & 0xff) << 16;
            case 2:
                k1 ^= ((long) data[index + 1] & 0xff) << 8;
            case 1:
                k1 ^= data[index] & 0xff;
                k1 *= C1;
                k1 = Long.rotateLeft(k1, R1);
                k1 *= C2;
                h1 ^= k1;
        }

        // finalization
        h1 ^= length;
        h2 ^= length;

        h1 += h2;
        h2 += h1;

        h1 = fmix64(h1);
        h2 = fmix64(h2);

        h1 += h2;
        h2 += h1;

        return new long[] { h1, h2 };
    }
}