IM/backend/IM_API/Services/SequenceIdService.cs

using IM_API.Interface.Services;
using IM_API.Models;
using IM_API.Tools;
using Microsoft.EntityFrameworkCore;
using RedLockNet;
using StackExchange.Redis;

namespace IM_API.Services
{
    public class SequenceIdService : ISequenceIdService
    {
        private IDatabase _database;
        private IDistributedLockFactory _lockFactory;
        private ImContext _context;
        public SequenceIdService(IConnectionMultiplexer connectionMultiplexer, 
            IDistributedLockFactory distributedLockFactory, ImContext imContext)
        {
            _database = connectionMultiplexer.GetDatabase();
            _lockFactory = distributedLockFactory;
            _context = imContext;
        }
        public async Task<long> GetNextSquenceIdAsync(string streamKey)
        {
            string key = RedisKeys.GetSequenceIdKey(streamKey);
            string lockKey = RedisKeys.GetSequenceIdLockKey(streamKey);
            var exists = await _database.KeyExistsAsync(key);
            if (!exists)
            {
                using (var _lock = await _lockFactory.CreateLockAsync(lockKey, TimeSpan.FromSeconds(5)))
                {
                    if (_lock.IsAcquired)
                    {
                        if(!await _database.KeyExistsAsync(key))
                        {
                            var max = await _context.Messages
                            .Where(x => x.StreamKey == streamKey)
                            .MaxAsync(m => (long?)m.SequenceId) ?? 0;
                            await _database.StringSetAsync(key, max, TimeSpan.FromDays(7));
                        }
                    }
                }
            }
            return await _database.StringIncrementAsync(key);
        }
    }
}