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/*
 * Copyright (C) 2012 The Guava Authors
 *
 * 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.
 */

/*
 * SipHash-c-d was designed by Jean-Philippe Aumasson and Daniel J. Bernstein and is described in
 * "SipHash: a fast short-input PRF" (available at https://131002.net/siphash/siphash.pdf).
 */

package com.landawn.abacus.hash;

import java.io.Serializable;
import java.nio.ByteBuffer;

import com.landawn.abacus.util.N;

/**
 * Note: It's copied from Google Guava under Apache License 2.0
 * 
 * {@link HashFunction} implementation of SipHash-c-d.
 *
 * @author Kurt Alfred Kluever
 * @author Jean-Philippe Aumasson
 * @author Daniel J. Bernstein
 */
final class SipHashFunction extends AbstractStreamingHashFunction implements Serializable {

    // The number of compression rounds.
    private final int c;
    // The number of finalization rounds.
    private final int d;
    // Two 64-bit keys (represent a single 128-bit key).
    private final long k0;
    private final long k1;

    /**
     * @param c the number of compression rounds (must be positive)
     * @param d the number of finalization rounds (must be positive)
     * @param k0 the first half of the key
     * @param k1 the second half of the key
     */
    SipHashFunction(int c, int d, long k0, long k1) {
        N.checkArgument(c > 0, "The number of SipRound iterations (c=%s) during Compression must be positive.", c);
        N.checkArgument(d > 0, "The number of SipRound iterations (d=%s) during Finalization must be positive.", d);
        this.c = c;
        this.d = d;
        this.k0 = k0;
        this.k1 = k1;
    }

    @Override
    public int bits() {
        return 64;
    }

    @Override
    public Hasher newHasher() {
        return new SipHasher(c, d, k0, k1);
    }

    // TODO(kak): Implement and benchmark the hashFoo() shortcuts.

    @Override
    public String toString() {
        return "Hashing.sipHash" + c + "" + d + "(" + k0 + ", " + k1 + ")";
    }

    @Override
    public boolean equals(Object object) {
        if (object instanceof SipHashFunction) {
            SipHashFunction other = (SipHashFunction) object;
            return (c == other.c) && (d == other.d) && (k0 == other.k0) && (k1 == other.k1);
        }
        return false;
    }

    @Override
    public int hashCode() {
        return (int) (getClass().hashCode() ^ c ^ d ^ k0 ^ k1);
    }

    private static final class SipHasher extends AbstractStreamingHasher {
        private static final int CHUNK_SIZE = 8;

        // The number of compression rounds.
        private final int c;
        // The number of finalization rounds.
        private final int d;

        // Four 64-bit words of internal state.
        // The initial state corresponds to the ASCII string "somepseudorandomlygeneratedbytes",
        // big-endian encoded. There is nothing special about this value; the only requirement
        // was some asymmetry so that the initial v0 and v1 differ from v2 and v3.
        private long v0 = 0x736f6d6570736575L;
        private long v1 = 0x646f72616e646f6dL;
        private long v2 = 0x6c7967656e657261L;
        private long v3 = 0x7465646279746573L;

        // The number of bytes in the input.
        private long b = 0;

        // The final 64-bit chunk includes the last 0 through 7 bytes of m followed by null bytes
        // and ending with a byte encoding the positive integer b mod 256.
        private long finalM = 0;

        SipHasher(int c, int d, long k0, long k1) {
            super(CHUNK_SIZE);
            this.c = c;
            this.d = d;
            this.v0 ^= k0;
            this.v1 ^= k1;
            this.v2 ^= k0;
            this.v3 ^= k1;
        }

        @Override
        protected void process(ByteBuffer buffer) {
            b += CHUNK_SIZE;
            processM(buffer.getLong());
        }

        @Override
        protected void processRemaining(ByteBuffer buffer) {
            b += buffer.remaining();
            for (int i = 0; buffer.hasRemaining(); i += 8) {
                finalM ^= (buffer.get() & 0xFFL) << i;
            }
        }

        @Override
        public HashCode makeHash() {
            // End with a byte encoding the positive integer b mod 256.
            finalM ^= b << 56;
            processM(finalM);

            // Finalization
            v2 ^= 0xFFL;
            sipRound(d);
            return HashCode.fromLong(v0 ^ v1 ^ v2 ^ v3);
        }

        private void processM(long m) {
            v3 ^= m;
            sipRound(c);
            v0 ^= m;
        }

        private void sipRound(int iterations) {
            for (int i = 0; i < iterations; i++) {
                v0 += v1;
                v2 += v3;
                v1 = Long.rotateLeft(v1, 13);
                v3 = Long.rotateLeft(v3, 16);
                v1 ^= v0;
                v3 ^= v2;
                v0 = Long.rotateLeft(v0, 32);
                v2 += v1;
                v0 += v3;
                v1 = Long.rotateLeft(v1, 17);
                v3 = Long.rotateLeft(v3, 21);
                v1 ^= v2;
                v3 ^= v0;
                v2 = Long.rotateLeft(v2, 32);
            }
        }
    }

    private static final long serialVersionUID = 0L;
}