using StackExchange.Redis;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace Easy.Realization;

internal static class IDatabaseExtension
{
    #region Distributed Locker
    internal static async Task<(bool Success, string LockValue)> LockAsync(this IDatabase redisDb, string cacheKey, int timeoutSeconds = 5, bool autoDelay = true)
    {

        var lockKey = GetLockKey(cacheKey);
        var lockValue = Guid.NewGuid().ToString();
        var timeoutMilliseconds = timeoutSeconds * 1000;
        var expiration = TimeSpan.FromMilliseconds(timeoutMilliseconds);
        bool flag = await redisDb.StringSetAsync(lockKey, lockValue, expiration, When.NotExists, CommandFlags.None);
        if (flag && autoDelay)
        {
            var refreshMilliseconds = (int)(timeoutMilliseconds / 2.0);
            var autoDelayTimer = new Timer(timerState => Delay(redisDb, lockKey, lockValue, timeoutMilliseconds), null, refreshMilliseconds, refreshMilliseconds);
            var addResult = AutoDelayTimers.TryAdd(lockKey, autoDelayTimer);
            if (!addResult)
            {
                autoDelayTimer?.Dispose();
                await redisDb.SafedUnLockAsync(cacheKey, lockValue);
                return (false, null);
            }
        }
        return (flag, flag ? lockValue : null);
    }

    internal static async Task<bool> SafedUnLockAsync(this IDatabase redisDb, string cacheKey, string lockValue)
    {
        var lockKey = GetLockKey(cacheKey);
        AutoDelayTimers.CloseTimer(lockKey);

        var script = @"local invalue = @value
                                    local currvalue = redis.call('get',@key)
                                    if(invalue==currvalue) then redis.call('del',@key)
                                        return 1
                                    else
                                        return 0
                                    end";
        var parameters = new { key = lockKey, value = lockValue };
        var prepared = LuaScript.Prepare(script);
        var result = (int)await redisDb.ScriptEvaluateAsync(prepared, parameters);
        return result == 1;
    }

    internal static void Delay(IDatabase redisDb, string key, string value, int milliseconds)
    {
        if (!AutoDelayTimers.ContainsKey(key))
            return;

        // local ttltime = redis.call('PTTL', @key)
        var script = @"local val = redis.call('GET', @key)
                                    if val==@value then
                                        redis.call('PEXPIRE', @key, @milliseconds)
                                        return 1
                                    end
                                    return 0";
        object parameters = new { key, value, milliseconds };
        var prepared = LuaScript.Prepare(script);
        var result = redisDb.ScriptEvaluateAsync(prepared, parameters, CommandFlags.None).GetAwaiter().GetResult();
        if ((int)result == 0)
        {
            AutoDelayTimers.CloseTimer(key);
        }
        return;
    }

    internal static string GetLockKey(string cacheKey)
    {
        return $"adnc:locker:{cacheKey.Replace(":", "-")}";
    }

    #endregion Distributed Locker

}