using F9WebAiTest.Application.Interfaces.SnowflakeID;

namespace F9WebAiTest.Infrastructure.InterfaceImplements.SnowflakeID;

/// <summary>
/// 雪花 ID 生成器（自实现，41 时间戳 + 10 worker + 12 序列）。
/// 参考 BBIT.F9.Infrastructure.InterfaceImplements.SnowflakeID.SnowflakeIdGenerator
/// </summary>
public class SnowflakeIdGenerator : ISnowflakeIdGenerator
{
    private readonly object _lock = new();
    private readonly long _workerId;
    private readonly long _epoch;
    private long _lastTimestamp = -1L;
    private long _sequence;

    private const long WorkerIdBits = 10L;
    private const long SequenceBits = 12L;
    private const long WorkerIdShift = SequenceBits;
    private const long TimestampShift = SequenceBits + WorkerIdBits;
    private const long SequenceMask = -1L ^ (-1L << (int)SequenceBits);

    public SnowflakeIdGenerator()
    {
        _workerId = 1; // 单节点默认 workerId = 1
        _epoch = new DateTimeOffset(2025, 10, 1, 0, 0, 0, TimeSpan.Zero).ToUnixTimeMilliseconds();
    }

    public long CreateId()
    {
        lock (_lock)
        {
            var timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() - _epoch;
            if (timestamp < _lastTimestamp)
                throw new InvalidOperationException("时钟回拨，拒绝生成 ID");

            if (timestamp == _lastTimestamp)
            {
                _sequence = (_sequence + 1) & SequenceMask;
                if (_sequence == 0)
                {
                    // 序列溢出，等待下一毫秒
                    while (timestamp <= _lastTimestamp)
                        timestamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() - _epoch;
                }
            }
            else
            {
                _sequence = 0;
            }

            _lastTimestamp = timestamp;

            return (timestamp << (int)TimestampShift)
                   | (_workerId << (int)WorkerIdShift)
                   | _sequence;
        }
    }
}