/*
 * 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.
 */

package org.tribuo.util;

/**
 *  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 {
        /**
         * First value.
         */
        public long val1;
        /**
         * Second value.
         */
        public long val2;
    }

    /**
     * 32-bit mixing function.
     * @param h Value to mix.
     * @return Mixed value.
     */
    public static final int fmix32(int h) {
        h ^= h >>> 16;
        h *= 0x85ebca6b;
        h ^= h >>> 13;
        h *= 0xc2b2ae35;
        h ^= h >>> 16;
        return h;
    }

    /**
     * 64-bit mixing function.
     * @param k Value to mix.
     * @return Mixed value.
     */
    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.
     * @param buf The buffer to operate on.
     * @param offset The current offset into the buffer.
     * @return A long.
     */
    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.
     * @param data The data to hash.
     * @param offset The offset into the data.
     * @param len The length of the data to hash.
     * @param seed The initial seed of the hash.
     * @return The murmurhash3_x86_32 hash.
     */
    public static int murmurhash3_x86_32(byte[] data, int offset, int len, int seed) {

        final int c1 = 0xcc9e2d51;
        final int c2 = 0x1b873593;

        int h1 = seed;
        int roundedEnd = offset + (len & 0xfffffffc);  // round down to 4 byte block

        for (int i=offset; i<roundedEnd; i+=4) {
            // little endian load order
            int k1 = (data[i] & 0xff) | ((data[i+1] & 0xff) << 8) | ((data[i+2] & 0xff) << 16) | (data[i+3] << 24);
            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;
        }

        // tail
        int k1 = 0;

        switch(len & 0x03) {
            case 3:
                k1 = (data[roundedEnd + 2] & 0xff) << 16;
                // fallthrough
            case 2:
                k1 |= (data[roundedEnd + 1] & 0xff) << 8;
                // fallthrough
            case 1:
                k1 |= (data[roundedEnd] & 0xff);
                k1 *= c1;
                k1 = (k1 << 15) | (k1 >>> 17);  // ROTL32(k1,15);
                k1 *= c2;
                h1 ^= k1;
        }

        // finalization
        h1 ^= len;

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

        return h1;
    }

    /**
     * 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().
     * @param data The data to hash.
     * @param offset The offset into the data.
     * @param len The length of the data to hash.
     * @param seed The initial seed of the hash.
     * @return The murmurhash3_x86_32 hash.
     */
    public static int murmurhash3_x86_32(CharSequence data, int offset, int len, int seed) {

        final int c1 = 0xcc9e2d51;
        final int c2 = 0x1b873593;

        int h1 = seed;

        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;

                /***
                 // optimized ascii implementation (currently slower!!! code size?)
                 if (shift == 24) {
                 k1 = k1 | (code << 24);
                 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 = 0;
                 nBytes += 4;
                 k1 = 0;
                 } else {
                 k1 |= code << shift;
                 shift += 8;
                 }
                 continue;
                 ***/

            }
            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;
    }

    /**
     * Returns the MurmurHash3_x64_128 hash, placing the result in "out".
     * @param key The data to hash.
     * @param offset The offset into the data.
     * @param len The length of the data to hash.
     * @param seed The initial state of the hash.
     * @param out The output value (as it's 128 bits).
     */
    public static void murmurhash3_x64_128(byte[] key, int offset, int len, int seed, LongPair out) {
        // The original algorithm does have a 32 bit unsigned seed.
        // We have to mask to match the behavior of the unsigned types and prevent sign extension.
        long h1 = seed & 0x00000000FFFFFFFFL;
        long h2 = seed & 0x00000000FFFFFFFFL;

        final long c1 = 0x87c37b91114253d5L;
        final long c2 = 0x4cf5ad432745937fL;

        int roundedEnd = offset + (len & 0xFFFFFFF0);  // round down to 16 byte block
        for (int i=offset; i<roundedEnd; i+=16) {
            long k1 = getLongLittleEndian(key, i);
            long k2 = getLongLittleEndian(key, i+8);
            k1 *= c1; k1  = Long.rotateLeft(k1,31); k1 *= c2; h1 ^= k1;
            h1 = Long.rotateLeft(h1,27); h1 += h2; h1 = h1*5+0x52dce729;
            k2 *= c2; k2  = Long.rotateLeft(k2,33); k2 *= c1; h2 ^= k2;
            h2 = Long.rotateLeft(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
        }

        long k1 = 0;
        long k2 = 0;

        switch (len & 15) {
            case 15: k2  = (key[roundedEnd+14] & 0xffL) << 48;
            case 14: k2 |= (key[roundedEnd+13] & 0xffL) << 40;
            case 13: k2 |= (key[roundedEnd+12] & 0xffL) << 32;
            case 12: k2 |= (key[roundedEnd+11] & 0xffL) << 24;
            case 11: k2 |= (key[roundedEnd+10] & 0xffL) << 16;
            case 10: k2 |= (key[roundedEnd+ 9] & 0xffL) << 8;
            case  9: k2 |= (key[roundedEnd+ 8] & 0xffL);
                k2 *= c2; k2  = Long.rotateLeft(k2, 33); k2 *= c1; h2 ^= k2;
            case  8: k1  = ((long)key[roundedEnd+7]) << 56;
            case  7: k1 |= (key[roundedEnd+6] & 0xffL) << 48;
            case  6: k1 |= (key[roundedEnd+5] & 0xffL) << 40;
            case  5: k1 |= (key[roundedEnd+4] & 0xffL) << 32;
            case  4: k1 |= (key[roundedEnd+3] & 0xffL) << 24;
            case  3: k1 |= (key[roundedEnd+2] & 0xffL) << 16;
            case  2: k1 |= (key[roundedEnd+1] & 0xffL) << 8;
            case  1: k1 |= (key[roundedEnd  ] & 0xffL);
                k1 *= c1; k1  = Long.rotateLeft(k1,31); k1 *= c2; h1 ^= k1;
        }

        //----------
        // finalization

        h1 ^= len; h2 ^= len;

        h1 += h2;
        h2 += h1;

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

        h1 += h2;
        h2 += h1;

        out.val1 = h1;
        out.val2 = h2;
    }

}