using Microsoft.Extensions.Logging;

namespace StopShopping.Services.Implementions;

public class SerialNoGenerator : ISerialNoGenerator
{
    public SerialNoGenerator(ILogger<SerialNoGenerator> logger)
    {
        _logger = logger;
    }

    private readonly ILogger<SerialNoGenerator> _logger;

    private const long START_UTC = 1767196800000; //2026-01-01 00:00:00.000
    private const int BITS_CALLBACK = 3;
    private const int BITS_SERIAL = 6;
    private const long MASK_CALLBACK = ~(-1L << BITS_CALLBACK); //0b_0111
    private const long MASK_SERIAL = ~(-1L << BITS_SERIAL);

    private readonly object _lockObj = new();

    private long _lastUtc = DateTimeOffset.Now.ToUnixTimeMilliseconds();
    private long _serial;
    private long _callbackSerial;

    /// <summary>
    /// <list type="table">
    /// <item>
    /// <term>
    /// 0000000
    /// </term>
    /// <term>
    /// 00000000000
    /// </term>
    /// <term>
    /// 00000000000
    /// </term>
    /// <term>
    /// 0000000000
    /// </term>
    /// </item>
    /// 
    /// <item>
    /// <term>
    /// 符号位1bit
    /// </term>
    /// </item>
    /// <term>
    /// 毫秒时间戳56bit
    /// </term>
    /// <term>
    /// 时间回拨标识3bit
    /// </term>
    /// <term>
    /// 毫秒内序号6bit
    /// </term>
    /// </list>
    /// </summary>
    /// <returns></returns>
    public string GenerateRequestNo()
    {
        lock (_lockObj)
        {
            var currUtc = DateTimeOffset.Now.ToUnixTimeMilliseconds();

            if (currUtc < _lastUtc) //时间回拨
            {
                currUtc = _lastUtc;
                _callbackSerial = (_callbackSerial + 1) & MASK_CALLBACK;
                if (_callbackSerial == 0) //时间回拨标识数据段用完
                {
                    _logger.LogWarning("服务器时间不准，序列号可能重复，请检查！");
                }
            }

            if (currUtc > _lastUtc)
            {
                _serial = 1;
                _callbackSerial = 0;
            }
            else
            {
                _serial = (_serial + 1) & MASK_SERIAL;
                if (_serial == 0) //毫秒内数据段用完
                {
                    WaitNextMilliSecond(ref currUtc);
                    _serial = 1;
                }
            }

            _lastUtc = currUtc;

            long serial = ((currUtc - START_UTC) << BITS_CALLBACK + BITS_SERIAL)
                | (_callbackSerial << BITS_SERIAL)
                | _serial;

            return string.Format("R{0}", serial);
        }
    }

    public string GenerateProductNo()
    {
        throw new NotImplementedException();
    }

    private void WaitNextMilliSecond(ref long curr)
    {
        while (_lastUtc >= curr)
        {
            curr = DateTimeOffset.Now.ToUnixTimeMilliseconds();
        }
    }

    public string GenerateRandomPassword()
    {
        throw new NotImplementedException();
    }
}