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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
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 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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/*
 * @test
 * @bug 8026236
 * @summary test primality verification methods in BigInteger
 * @author bpb
 */

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.List;
import java.util.Random;
import static java.util.stream.Collectors.toList;
import java.util.stream.Stream;
import java.util.zip.GZIPInputStream;

public class PrimeTest {
    private static final String DEFAULT_PRIMES_FILE;
    private static final int DEFAULT_UPPER_BOUND = 1000000;
    private static final int DEFAULT_CERTAINTY = 100;

    static {
        try {
            String dir = System.getProperty("test.src", ".");
            File testFile = new File(dir, "primes-100000.txt.gz");
            DEFAULT_PRIMES_FILE = testFile.getAbsolutePath();
        } catch (Throwable t) {
            throw new Error(t);
        }
    }

    public static void main(String[] args) throws Throwable {
        // Prepare arguments
        File primesFile = args.length > 0 ? new File(args[0]) : new File(DEFAULT_PRIMES_FILE);
        int upperBound = args.length > 1 ? Integer.valueOf(args[1]) : DEFAULT_UPPER_BOUND;
        int certainty = args.length > 2 ? Integer.valueOf(args[2]) : DEFAULT_CERTAINTY;
        boolean parallel = args.length > 3 ? Boolean.valueOf(args[3]) : true;

        // Echo parameter settings
        System.out.println("Primes: " + primesFile + "\nupper bound = " + upperBound
                + "\ncertainty = " + certainty
                + "\nparallel = " + parallel);

        boolean primeTest = checkPrime(primesFile, upperBound, certainty, parallel);
        System.out.println("Prime test result: " + (primeTest ? "SUCCESS" : "FAILURE"));
        if (!primeTest) {
            System.err.println("Prime test failed");
        }

        boolean notPrimeTest = checkNotPrime(primesFile, upperBound, certainty);
        System.out.println("Not-prime test result: " + (notPrimeTest ? "SUCCESS" : "FAILURE"));

        if (!primeTest || !notPrimeTest) {
            throw new Exception("PrimeTest FAILED!");
        }
        System.out.println("PrimeTest succeeded!");
    }

    /**
     * Parse the primes into a list of [@code BigInteger}s.
     *
     * @param f File of prime numbers assumed to be a GZIPped text file with one
     * number per line in the default character set
     * @param n The maximum number of primes to load
     * @return A {@code List<BigInteger>} containing the loaded primes
     * @throws IOException If something nasty happens
     */
    private static List<BigInteger> parsePrimes(File f, long n) throws IOException {
        GZIPInputStream gis = new GZIPInputStream(new FileInputStream(f));
        BufferedReader br = new BufferedReader(new InputStreamReader(gis));
        try (Stream<String> lines = br.lines()) {
            return lines.limit(n).map(BigInteger::new).collect(toList());
        }
    }

    /**
     * Verifies whether the fraction of probable primes detected in the range
     * [2,upperBound) is at least 1 - 1/2^certainty.
     *
     * @return true if and only if the test succeeds
     */
    private static boolean checkPrime(File primesFile, int upperBound,
            int certainty,
            boolean parallel) throws FileNotFoundException, IOException {

        List<BigInteger> primes = parsePrimes(primesFile, upperBound);

        System.out.println(String.format("Loaded %d primes", primes.size()));

        long probablePrimes = (parallel ? primes.parallelStream() : primes.stream())
                .filter(bi -> bi.isProbablePrime(certainty))
                .count();

        System.out.println(probablePrimes + " probable primes out of " +
                primes.size() + " candidates");
        if (probablePrimes != primes.size()) {
            System.err.println("Number of probable primes unequal to number of actual primes");
        }

        // N = certainty / 2
        // Success if p/t >= 1 - 1/4^N
        // or (p/t)*4^N >= 4^N - 1
        // or p*4^N >= t*(4^N - 1)
        BigInteger p = BigInteger.valueOf(probablePrimes);
        BigInteger t = BigInteger.valueOf(primes.size());
        BigInteger fourToTheC = BigInteger.valueOf(4).pow(certainty / 2);
        BigInteger fourToTheCMinusOne = fourToTheC.subtract(BigInteger.ONE);
        BigInteger left = p.multiply(fourToTheC);
        BigInteger right = t.multiply(fourToTheCMinusOne);

        if (left.compareTo(right) < 0) {
            System.err.println("Probable prime certainty test failed.");
        }

        return left.compareTo(right) >= 0;
    }

    /**
     * Verifies whether all {@code BigInteger}s in the range [2,upperBound) for
     * which {@code isProbablePrime()} returns {@code false} are <i>not</i>
     * prime numbers.
     *
     * @return true if and only if the test succeeds
     */
    private static boolean checkNotPrime(File primesFile, int upperBound,
            int certainty) throws FileNotFoundException, IOException {
        List<BigInteger> primes = parsePrimes(primesFile, upperBound);

        // If it's not a probable prime but is in the primes list then fail.
        boolean result = !(new Random()).ints(2500, 0, 100000).mapToObj(i -> {return BigInteger.valueOf(i);}).filter(b -> !b.isProbablePrime(certainty)).anyMatch(c -> primes.contains(c));

        return result;
    }
}