/*
 * 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 hivemall.utils.hashing;

import hivemall.utils.math.MathUtils;

public final class MurmurHash3 {

    /** 2^24 */
    public static final int DEFAULT_NUM_FEATURES = 16777216;

    /**
     * @return hash value of range from 0 to 2^24 (16777216).
     */
    public static int murmurhash3(final String data) {
        final int h = murmurhash3_x86_32(data, 0, data.length(), 0x9747b28c);
        int r = MathUtils.moduloPowerOfTwo(h, DEFAULT_NUM_FEATURES);
        if (r < 0) {
            r += DEFAULT_NUM_FEATURES;
        }
        return r;
    }

    public static int murmurhash3(final String data, final int numFeatures) {
        int r = murmurhash3_x86_32(data, 0, data.length(), 0x9747b28c) % numFeatures;
        if (r < 0) {
            r += numFeatures;
        }
        return r;
    }

    public static int murmurhash3_x86_32(final String data) {
        return murmurhash3_x86_32(data, 0x9747b28c);
    }

    public static int murmurhash3_x86_32(final String data, final int seed) {
        return murmurhash3_x86_32(data, 0, data.length(), seed);
    }

    /** Returns the MurmurHash3_x86_32 hash. */
    public static int murmurhash3_x86_32(final CharSequence data, final int offset, final int len,
            final int seed) {
        final int c1 = 0xcc9e2d51;
        final int c2 = 0x1b873593;

        int h1 = seed;
        final int end = offset + len;
        int pos = offset;
        int k1 = 0;
        int k2 = 0;
        int shift = 0;
        int bits = 0;
        int nBytes = 0; // length in UTF8 bytes

        while (pos < end) {
            final 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;

            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;
    }
}