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/**
 * Copyright 2010 - 2022 JetBrains s.r.o.
 *
 * 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
 *
 * https://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 jetbrains.exodus.util;

/**
 * Non-concurrent replacement of java.util.Random.
 */
public class Random {

    private static final long multiplier = 0x5DEECE66DL;
    private static final long addend = 0xBL;
    private static final long mask = (1L << 48) - 1;

    private long seed;

    public Random() {
        reset();
    }

    public Random(long seed) {
        setSeed(seed);
    }

    public int nextInt() {
        return next(32);
    }

    public int nextInt(int n) {
        if (n <= 0)
            throw new IllegalArgumentException("n must be positive");

        if ((n & -n) == n)  // i.e., n is a power of 2
            return (int) ((n * (long) next(31)) >> 31);

        int bits, val;
        do {
            bits = next(31);
            val = bits % n;
        } while (bits - val + (n - 1) < 0);
        return val;
    }

    public long nextLong() {
        // it's okay that the bottom word remains signed.
        return ((long) (next(32)) << 32) + next(32);
    }

    public boolean nextBoolean() {
        return next(1) != 0;
    }

    public float nextFloat() {
        return next(24) / ((float) (1 << 24));
    }

    public double nextDouble() {
        return (((long) (next(26)) << 27) + next(27)) / (double) (1L << 53);
    }

    public void nextBytes(byte[] bytes) {
        int i = 0;
        int len = bytes.length;
        while (i < len)
            for (int rnd = nextInt(),
                         n = Math.min(len - i, Integer.SIZE / Byte.SIZE);
                 n-- > 0; rnd >>= Byte.SIZE)
                bytes[i++] = (byte) rnd;
    }

    public void setSeed(long seed) {
        this.seed = (seed ^ multiplier) & mask;
        for (int i = 0; i < 10; ++i) {
            nextInt();
        }
    }

    public void reset() {
        setSeed(System.currentTimeMillis());
    }

    public int next(int bits) {
        seed = (seed * multiplier + addend) & mask;
        return (int) (seed >>> (48 - bits));
    }
}