CloudCharging -<<redis-stack-charge_request_redis-lambda-fn >>

ChargingEngineService.cs

using StackExchange.Redis;
using System;
using System.Threading.Tasks;

public class ChargingEngineService
{
    private static readonly string Key = "account1/balance";
    private static readonly int DefaultBalance = 100;
    private static ConnectionMultiplexer redis;

    public static async Task<ChargeResult> ChargeRequestAsync()
    {
        var db = await GetDatabaseAsync();
        var remainingBalance = await GetBalanceAsync(db, Key);
        var charges = GetCharges();
        var isAuthorized = remainingBalance >= charges;

        if (!isAuthorized)
        {
            return new ChargeResult
            {
                RemainingBalance = remainingBalance,
                IsAuthorized = false,
                Charges = 0
            };
        }

        var newRemainingBalance = await ChargeAsync(db, Key, charges);

        return new ChargeResult
        {
            RemainingBalance = newRemainingBalance,
            IsAuthorized = true,
            Charges = charges
        };
    }

    public static async Task<int> ResetAsync()
    {
        var db = await GetDatabaseAsync();
        await db.StringSetAsync(Key, DefaultBalance);
        return DefaultBalance;
    }

    private static async Task<IDatabase> GetDatabaseAsync()
    {
        if (redis == null || !redis.IsConnected)
        {
            redis = await ConnectionMultiplexer.ConnectAsync($"{Environment.GetEnvironmentVariable("ENDPOINT")}:{Environment.GetEnvironmentVariable("PORT") ?? "6379"}");
        }

        return redis.GetDatabase();
    }

    private static int GetCharges()
    {
        return DefaultBalance / 20;
    }

    private static async Task<int> GetBalanceAsync(IDatabase db, string key)
    {
        var res = await db.StringGetAsync(key);
        return (int)res;
    }

    private static async Task<int> ChargeAsync(IDatabase db, string key, int charges)
    {
        return (int)await db.StringDecrementAsync(key, charges);
    }
}

public class ChargeResult
{
    public int RemainingBalance { get; set; }
    public int Charges { get; set; }
    public bool IsAuthorized { get; set; }
}