package jp.nekopippi;

import java.io.IOException;
import static java.lang.Math.abs;
import java.util.Arrays;
import java.util.Random;
import java.util.stream.IntStream;
import java.nio.ByteBuffer;
import java.nio.channels.ByteChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.Files;
import static java.nio.file.StandardOpenOption.READ;
import org.junit.*;
import static org.junit.Assert.*;

public class PseudoRandomTest {
    private static ByteChannel urandom;
    private ByteBuffer mBuf;

    @BeforeClass
    public static void openUrandom() throws IOException {
        final Path p = Paths.get("/dev/urandom");
        urandom = Files.newByteChannel(p, READ);
    }

    @AfterClass
    public static void closeFiles() throws IOException {
        if (urandom != null) {
            urandom.close();
        }
    }

    @Before
    public void initBuffer() {
        mBuf = ByteBuffer.allocate(16);
    }

    @Test
    public void testFirst512Bits10Times() {
        assertEquals(
            IntStream.range(0, 10)
                .map(ignore -> {
                    final long seed = getSeed();
                    final Random prng1 = new Random(seed);
                    final Random prng2 = new Random(seed);

                    final long l1 = prng1.nextLong();
                    final long l2 = prng2.nextLong();
                    return Long.compare(l1, l2);
                })
                .reduce(0, (a, v) -> a + abs(v)),
            0);
    }

    @Test
    public void testFirst65536Bits() {
        final long seed = getSeed();
        final Random prng1 = new Random(seed);
        final Random prng2 = new Random(seed);
        // 128 * 64 * 8 = 65536
        IntStream.range(0, 128).forEach(ignore -> {
            final long l1 = prng1.nextLong();
            final long l2 = prng2.nextLong();
            assertEquals(l1, l2);
        });
    }

    private final long getSeed() {
        mBuf.clear();
        try {
            urandom.read(mBuf);
        } catch (IOException e) {
            fail(e.toString());
        }
        mBuf.flip();
        final long seed = mBuf.getLong();
        return seed;
    }
}