btcpayserver/BTCPayServer/Services/Rates/CachedRateProvider.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using BTCPayServer.Services.Rates;
using Microsoft.Extensions.Caching.Memory;

namespace BTCPayServer.Services.Rates
{
	public class CachedRateProvider : IRateProvider
	{
		private IRateProvider _Inner;
		private IMemoryCache _MemoryCache;

		public CachedRateProvider(IRateProvider inner, IMemoryCache memoryCache)
		{
			if(inner == null)
				throw new ArgumentNullException(nameof(inner));
			if(memoryCache == null)
				throw new ArgumentNullException(nameof(memoryCache));
			this._Inner = inner;
			this._MemoryCache = memoryCache;
		}

		public TimeSpan CacheSpan
		{
			get;
			set;
		} = TimeSpan.FromMinutes(1.0);

		public Task<decimal> GetRateAsync(string currency)
		{
			return _MemoryCache.GetOrCreateAsync("CURR_" + currency, (ICacheEntry entry) =>
			{
				entry.AbsoluteExpiration = DateTimeOffset.UtcNow + CacheSpan;
				return _Inner.GetRateAsync(currency);
			});
		}

		private bool TryGetFromCache(string key, out object obj)
		{
			obj = _MemoryCache.Get(key);
			return obj != null;
		}

		public Task<ICollection<Rate>> GetRatesAsync()
		{
			return _MemoryCache.GetOrCreateAsync("GLOBAL_RATES", (ICacheEntry entry) =>
			{
				entry.AbsoluteExpiration = DateTimeOffset.UtcNow + CacheSpan;
				return _Inner.GetRatesAsync();
			});
		}
	}
}