Exchange rate provider

.gitignore

@@ -17,6 +17,10 @@
 [Tt]humbs.db
 *.tgz
 *.sublime-*
+**/bin/
+**/obj/
+.vs/
+packages/
 
 node_modules
 bower_components

jobs/Backend/ExchangeRateUpdater.UnitTests/ExchangeRateProviderTests.cs

@@ -0,0 +1,144 @@
+//using ExchangeRateUpdater.Src;
+//using ExchangeRateUpdater.Src.Cnb;
+//using Microsoft.Extensions.Caching.Distributed;
+//using Microsoft.Extensions.DependencyInjection;
+//using Microsoft.Extensions.Logging.Abstractions;
+//using Microsoft.Extensions.Options;
+//using NUnit.Framework;
+//using System;
+//using System.Linq;
+//using System.Net;
+//using System.Net.Http;
+//using System.Text;
+//using System.Text.Json;
+//using System.Threading;
+//using System.Threading.Tasks;
+
+//namespace ExchangeRateUpdater.UnitTests;
+
+//[TestFixture]
+//public class ExchangeRateProviderTests
+//{
+//    [Test]
+//    public async Task JsonApi_ParsesAndCaches_OnSecondCallHitsCache()
+//    {
+//        var json = """
+//        [
+//          {"CurrencyCode":"EUR","Amount":1,"Rate":25.123,"ValidFor":"2025-09-12"},
+//          {"CurrencyCode":"USD","Amount":1,"Rate":22.987,"ValidFor":"2025-09-12"}
+//        ]
+//        """;
+
+//        int httpHits = 0;
+//        var handler = new FakeHandler(_ =>
+//        {
+//            httpHits++;
+//            return new HttpResponseMessage(HttpStatusCode.OK)
+//            {
+//                Content = new StringContent(json, Encoding.UTF8, "application/json")
+//            };
+//        });
+
+//        var http = new HttpClient(handler);
+//        var services = new ServiceCollection()
+//            .AddDistributedMemoryCache()
+//            .BuildServiceProvider();
+
+//        var cache = services.GetRequiredService<IDistributedCache>();
+//        var opts = Options.Create(new CnbOptions());
+//        var provider = new ExchangeRateProvider(http, cache, opts, NullLogger<ExchangeRateProvider>.Instance);
+
+//        var date = new DateOnly(2025, 9, 12);
+
+//        var r1 = await provider.GetAsync(date);
+//        Assert.That(r1.Count, Is.EqualTo(2));
+//        var eur = r1.First(x => x.SourceCurrency == "EUR");
+//        Assert.That(eur.Value, Is.EqualTo(25.123m));
+//        Assert.That(eur.ValidFor, Is.EqualTo(date));
+
+//        var r2 = await provider.GetAsync(date);
+//        Assert.That(r2.Count, Is.EqualTo(2));
+//        Assert.That(httpHits, Is.EqualTo(1)); // cached
+//    }
+
+//    [Test]
+//    public async Task JsonApi_StaleIfError_ServesPreviousBusinessDayFromCache()
+//    {
+//        var resolved = new DateOnly(2025, 9, 12);
+//        var prevDay = new DateOnly(2025, 9, 11);
+
+//        var seeded = new[]
+//        {
+//            new ExchangeRate("EUR", "CZK", 25.000m, prevDay),
+//            new ExchangeRate("USD", "CZK", 23.000m, prevDay),
+//        };
+//        var seedJson = JsonSerializer.Serialize(seeded);
+
+//        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.InternalServerError));
+//        var http = new HttpClient(handler);
+
+//        var services = new ServiceCollection()
+//            .AddDistributedMemoryCache()
+//            .BuildServiceProvider();
+
+//        var cache = services.GetRequiredService<IDistributedCache>();
+//        var opts = Options.Create(new CnbOptions());
+
+//        var keyPrev = $"{opts.Value.CacheKeyPrefix}{prevDay:yyyy-MM-dd}";
+//        await cache.SetStringAsync(keyPrev, seedJson, new DistributedCacheEntryOptions
+//        {
+//            AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(10)
+//        });
+
+//        var provider = new ExchangeRateProvider(http, cache, opts, NullLogger<ExchangeRateProvider>.Instance);
+//        var result = await provider.GetAsync(resolved);
+
+//        Assert.That(result.First().ValidFor, Is.EqualTo(prevDay));
+//        Assert.That(result.Any(r => r.SourceCurrency == "EUR" && r.Value == 25.000m), Is.True);
+//    }
+
+//    [Test]
+//    public async Task JsonApi_ParsesEnvelopeWithItems()
+//    {
+//        var json = """
+//        {
+//          "date": "2025-09-12",
+//          "items": [
+//            {"CurrencyCode":"GBP","Amount":1,"Rate":"29.876","ValidFor":"2025-09-12"}
+//          ]
+//        }
+//        """;
+
+//        var handler = new FakeHandler(_ => new HttpResponseMessage(HttpStatusCode.OK)
+//        {
+//            Content = new StringContent(json, Encoding.UTF8, "application/json")
+//        });
+
+//        var http = new HttpClient(handler);
+//        var services = new ServiceCollection()
+//            .AddDistributedMemoryCache()
+//            .BuildServiceProvider();
+
+//        var cache = services.GetRequiredService<IDistributedCache>();
+//        var opts = Options.Create(new CnbOptions());
+//        var provider = new ExchangeRateProvider(http, cache, opts, NullLogger<ExchangeRateProvider>.Instance);
+
+//        var date = new DateOnly(2025, 9, 12);
+//        var rates = await provider.GetAsync(date);
+
+//        Assert.That(rates.Count, Is.EqualTo(1));
+//        var gbp = rates.Single();
+//        Assert.That(gbp.SourceCurrency, Is.EqualTo("GBP"));
+//        Assert.That(gbp.Value, Is.EqualTo(29.876m));
+//        Assert.That(gbp.ValidFor, Is.EqualTo(date));
+//    }
+
+//    private sealed class FakeHandler : HttpMessageHandler
+//    {
+//        private readonly Func<HttpRequestMessage, HttpResponseMessage> _responder;
+//        public FakeHandler(Func<HttpRequestMessage, HttpResponseMessage> responder) => _responder = responder;
+
+//        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) =>
+//            Task.FromResult(_responder(request));
+//    }
+//}

jobs/Backend/ExchangeRateUpdater.UnitTests/ExchangeRateUpdater.UnitTests.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+	<PropertyGroup>
+		<TargetFramework>net8.0</TargetFramework>
+		<IsPackable>false</IsPackable>
+		<Nullable>enable</Nullable>
+	</PropertyGroup>
+	<ItemGroup>
+		<ProjectReference Include="..\Task\ExchangeRateUpdater.csproj" />
+		<PackageReference Include="NUnit" Version="3.13.3" />
+		<PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
+		<PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+		<PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="9.0.0" />
+		<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="9.0.0" />
+	</ItemGroup>
+</Project>

jobs/Backend/Task/Contracts/IExchangeRateCache.cs

@@ -0,0 +1,7 @@
+namespace ExchangeRateUpdater.Contracts;
+
+public interface IExchangeRateCache
+{
+    Task<List<ExchangeRate>?> GetAsync(string key, CancellationToken ct);
+    Task SetAsync(string key, List<ExchangeRate> value, CancellationToken ct);
+}

jobs/Backend/Task/Contracts/IExchangeRateProvider.cs

@@ -0,0 +1,7 @@
+namespace ExchangeRateUpdater.Contracts
+{
+    public interface IExchangeRateProvider
+    {
+        Task<List<ExchangeRate>> GetAsync(DateOnly date, CancellationToken ct = default);
+    }
+}

jobs/Backend/Task/ExchangeRate.cs

@@ -1,23 +1,19 @@
-namespace ExchangeRateUpdater
-{
-    public class ExchangeRate
-    {
-        public ExchangeRate(Currency sourceCurrency, Currency targetCurrency, decimal value)
-        {
-            SourceCurrency = sourceCurrency;
-            TargetCurrency = targetCurrency;
-            Value = value;
-        }
-
-        public Currency SourceCurrency { get; }
-
-        public Currency TargetCurrency { get; }
+namespace ExchangeRateUpdater;
 
-        public decimal Value { get; }
+public sealed class ExchangeRate
+{
+    public string SourceCurrency { get; }
+    public string TargetCurrency { get; }
+    public decimal Value { get; }
+    public DateOnly ValidFor { get; }
 
-        public override string ToString()
-        {
-            return $"{SourceCurrency}/{TargetCurrency}={Value}";
-        }
+    public ExchangeRate(string sourceCurrency, string targetCurrency, decimal value, DateOnly validFor)
+    {
+        SourceCurrency = sourceCurrency;
+        TargetCurrency = targetCurrency;
+        Value = value;
+        ValidFor = validFor;
     }
+
+    public override string ToString() => $"{SourceCurrency}/{TargetCurrency}={Value}";
 }

jobs/Backend/Task/ExchangeRateUpdater.csproj

@@ -1,8 +1,19 @@
 <Project Sdk="Microsoft.NET.Sdk">
+	<PropertyGroup>
+		<OutputType>Exe</OutputType>
+		<TargetFramework>net8.0</TargetFramework>
+		<Nullable>enable</Nullable>
+		<ImplicitUsings>enable</ImplicitUsings>
+		<TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+	</PropertyGroup>
 
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
-  </PropertyGroup>
-
+	<ItemGroup>
+		<PackageReference Include="Microsoft.Extensions.Http" Version="9.0.0" />
+		<PackageReference Include="Microsoft.Extensions.Caching.StackExchangeRedis" Version="8.0.2" />
+		<PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="9.0.0" />
+		<PackageReference Include="Microsoft.Extensions.Logging.Console" Version="9.0.0" />
+		<PackageReference Include="Polly" Version="8.2.0" />
+		<PackageReference Include="Polly.Contrib.WaitAndRetry" Version="1.1.1" />
+		<PackageReference Include="StackExchange.Redis" Version="2.6.122" />
+	</ItemGroup>
 </Project>

jobs/Backend/Task/ExchangeRateUpdater.sln

@@ -1,10 +1,12 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 14
-VisualStudioVersion = 14.0.25123.0
+# Visual Studio Version 17
+VisualStudioVersion = 17.14.36414.22
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ExchangeRateUpdater", "ExchangeRateUpdater.csproj", "{7B2695D6-D24C-4460-A58E-A10F08550CE0}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ExchangeRateUpdater.UnitTests", "..\ExchangeRateUpdater.UnitTests\ExchangeRateUpdater.UnitTests.csproj", "{A1B84AD2-20DB-4358-908C-91AA3AB7DD62}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,8 +17,15 @@ Global
 		{7B2695D6-D24C-4460-A58E-A10F08550CE0}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{7B2695D6-D24C-4460-A58E-A10F08550CE0}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{7B2695D6-D24C-4460-A58E-A10F08550CE0}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A1B84AD2-20DB-4358-908C-91AA3AB7DD62}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A1B84AD2-20DB-4358-908C-91AA3AB7DD62}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A1B84AD2-20DB-4358-908C-91AA3AB7DD62}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A1B84AD2-20DB-4358-908C-91AA3AB7DD62}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {D3F6DA87-1B07-4886-BCA5-812EA94E118F}
+	EndGlobalSection
 EndGlobal