namespace MasstransferCommon.Utils;

using System;

public class SnowflakeId
{
    private static readonly DateTime Epoch = new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc);
    private const int WorkerIdBits = 5;
    private const int DatacenterIdBits = 5;
    private const int SequenceBits = 12;

    private const long MaxWorkerId = -1L ^ (-1L << WorkerIdBits);
    private const long MaxDatacenterId = -1L ^ (-1L << DatacenterIdBits);

    private const long WorkerIdShift = SequenceBits;
    private const long DatacenterIdShift = SequenceBits + WorkerIdBits;
    private const long TimestampLeftShift = SequenceBits + WorkerIdBits + DatacenterIdBits;
    private const long SequenceMask = -1L ^ (-1L << SequenceBits);

    private readonly object _lock = new object();
    private long _lastTimestamp = -1L;
    private long _sequence = 0L;

    private static readonly SnowflakeId Instance = new SnowflakeId(0, 0);

    public long WorkerId { get; }
    public long DatacenterId { get; }

    public SnowflakeId(long workerId, long datacenterId)
    {
        if (workerId > MaxWorkerId || workerId < 0)
        {
            throw new ArgumentException($"workerId must be between 0 and {MaxWorkerId}");
        }

        if (datacenterId > MaxDatacenterId || datacenterId < 0)
        {
            throw new ArgumentException($"datacenterId must be between 0 and {MaxDatacenterId}");
        }

        WorkerId = workerId;
        DatacenterId = datacenterId;
    }

    public static string GetNextId()
    {
        return Instance.NextId().ToString();
    }

    private long NextId()
    {
        lock (_lock)
        {
            var timestamp = TimeGen();

            if (timestamp < _lastTimestamp)
            {
                throw new InvalidOperationException("Clock moved backwards. Refusing to generate id");
            }

            if (_lastTimestamp == timestamp)
            {
                _sequence = (_sequence + 1) & SequenceMask;
                if (_sequence == 0)
                {
                    timestamp = TilNextMillis(_lastTimestamp);
                }
            }
            else
            {
                _sequence = 0L;
            }

            _lastTimestamp = timestamp;

            return ((timestamp - EpochTicks()) << (int)TimestampLeftShift) |
                   (DatacenterId << (int)DatacenterIdShift) |
                   (WorkerId << (int)WorkerIdShift) |
                   _sequence;
        }
    }

    private long TilNextMillis(long lastTimestamp)
    {
        var timestamp = TimeGen();
        while (timestamp <= lastTimestamp)
        {
            timestamp = TimeGen();
        }

        return timestamp;
    }

    private long TimeGen()
    {
        return (long)(DateTime.UtcNow - Epoch).TotalMilliseconds;
    }

    private static long EpochTicks()
    {
        return (long)(Epoch - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds;
    }
}