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package cn.vonce.sql.uitls;

//import org.slf4j.Logger;
//import org.slf4j.LoggerFactory;

import java.io.Serializable;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.concurrent.RunnableFuture;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 廖雪峰的 53 bits unique id:
 * 53bitID由32bit秒级时间戳+16bit自增+5bit机器标识组成，累积32台机器，每秒可以生成6.5万个序列号
 * 
 * |--------|--------|--------|--------|--------|--------|--------|--------|
 * |00000000|00011111|11111111|11111111|11111111|11111111|11111111|11111111|
 * |--------|---xxxxx|xxxxxxxx|xxxxxxxx|xxxxxxxx|xxx-----|--------|--------|
 * |--------|--------|--------|--------|--------|---xxxxx|xxxxxxxx|xxx-----|
 * |--------|--------|--------|--------|--------|--------|--------|---xxxxx|
 * 

 * Maximum ID = 11111_11111111_11111111_11111111_11111111_11111111_11111111
 * 

 * Maximum TS = 11111_11111111_11111111_11111111_111
 * 

 * Maximum NT = ----- -------- -------- -------- ---11111_11111111_111 = 65535
 * 

 * Maximum SH = ----- -------- -------- -------- -------- -------- ---11111 = 31
 * 
 * It can generate 64k unique id per IP and up to 2106-02-07T06:28:15Z.
 */
public final class SnowflakeId16 implements Serializable {

//    private static final Logger logger = LoggerFactory.getLogger(SnowflakeId16.class);

    private static final Pattern PATTERN_LONG_ID = Pattern.compile("^([0-9]{15})([0-9a-f]{32})([0-9a-f]{3})$");

    private static final Pattern PATTERN_HOSTNAME = Pattern.compile("^.*\\D+([0-9]+)$");

    //暂时不支持jdk8
    //private static final long OFFSET = LocalDate.of(2000, 1, 1).atStartOfDay(ZoneId.of("Z")).toEpochSecond();
    private static final long OFFSET = 946684800;

    private static final long MAX_NEXT = 0b11111_11111111_111L;

    private static final long SHARD_ID = getServerIdAsLong();

    private static long offset = 0;

    private static long lastEpoch = 0;

    public static long nextId() {
        return nextId(System.currentTimeMillis() / 1000);
    }

    private static synchronized long nextId(long epochSecond) {
        if (epochSecond < lastEpoch) {
            // warning: clock is turn back:
//            logger.warn("clock is back: " + epochSecond + " from previous:" + lastEpoch);
            epochSecond = lastEpoch;
        }
        if (lastEpoch != epochSecond) {
            lastEpoch = epochSecond;
            reset();
        }
        offset++;
        long next = offset & MAX_NEXT;
        if (next == 0) {
//            logger.warn("maximum id reached in 1 second in epoch: " + epochSecond);
            return nextId(epochSecond + 1);
        }
        return generateId(epochSecond, next, SHARD_ID);
    }

    private static void reset() {
        offset = 0;
    }

    private static long generateId(long epochSecond, long next, long shardId) {
        return ((epochSecond - OFFSET) << 21) | (next << 5) | shardId;
    }

    private static long getServerIdAsLong() {
        try {
            //为照顾安卓版需异步调用
            RunnableFuture runnableFuture = new FutureTask<>(new Callable() {
                @Override
                public String call() throws UnknownHostException {
                    return InetAddress.getLocalHost().getHostName();
                }
            });
            new Thread(runnableFuture).start();
            String hostname = runnableFuture.get();
            Matcher matcher = PATTERN_HOSTNAME.matcher(hostname);
            if (matcher.matches()) {
                long n = Long.parseLong(matcher.group(1));
                if (n >= 0 && n < 8) {
//                    logger.info("detect server id from host name {}: {}.", hostname, n);
                    return n;
                }
            }
        } catch (ExecutionException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return 0;
    }

    public static long stringIdToLongId(String stringId) {
        // a stringId id is composed as timestamp (15) + uuid (32) + serverId (000~fff).
        Matcher matcher = PATTERN_LONG_ID.matcher(stringId);
        if (matcher.matches()) {
            long epoch = Long.parseLong(matcher.group(1)) / 1000;
            String uuid = matcher.group(2);
            byte[] sha1 = HashUtil.sha1AsBytes(uuid);
            long next = ((sha1[0] << 24) | (sha1[1] << 16) | (sha1[2] << 8) | sha1[3]) & MAX_NEXT;
            long serverId = Long.parseLong(matcher.group(3), 16);
            return generateId(epoch, next, serverId);
        }
        throw new IllegalArgumentException("Invalid id: " + stringId);
    }
}