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package com.ajjpj.abase.util;

import javax.xml.bind.DatatypeConverter;
import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * This is a far more efficient alternative to using java.com.ajjpj.abase.com.ajjpj.abase.util.UUID.randomUUID(), which uses a SecureRandom and
 *  uses excessive amounts of time. It creates a 20 byte identifier that is pretty sure to be unique.
 *
 * NB: This class does not produce 'real' UUID (i.e. its results do not conform to RFC 4122).

 *
 * NB: The ids generated by this class are neither uniformly distributed, nor do they have any other of the
 *  security related properties that java.lang.UUID.randomUUID() has. 
 *
 * NB: This implementation assumes that the system time progresses monotonously, i.e. it never moves 'backwards'.
 *
 * @author arno
 */
public class AUUID {
    private static final byte[] jvmIdentifier = createUniquePart();
    private static final AtomicInteger counter = new AtomicInteger(0);

    private final byte[] data;

    public static AUUID createRandom() {
        final int count = counter.incrementAndGet();
        final long timestamp = System.currentTimeMillis();

        final ByteBuffer result = ByteBuffer.allocate(20);
        result.put(jvmIdentifier);
        result.putLong(timestamp);
        result.putInt(count);
        return fromBytes(result.array());
    }

    public static AUUID fromBytes(byte[] data) {
        return new AUUID(data);
    }

    public static AUUID fromString(String data) {
        return fromBytes(DatatypeConverter.parseBase64Binary(data));
    }

    private AUUID(byte[] data) {
        this.data = data;
    }

    public byte[] getData() {
        return data;
    }

    public String toString() {
        return DatatypeConverter.printBase64Binary(data);
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        final AUUID auuid = (AUUID) o;

        return Arrays.equals(data, auuid.data);
    }

    @Override
    public int hashCode() {
        return data != null ? Arrays.hashCode(data) : 0;
    }

    private static byte[] createUniquePart() {
        final byte[] result = new byte[8];
        new SecureRandom().nextBytes(result);
        return result;
    }
}