Dotnet Backend ExchangeRateUpdater

jobs/Backend/Task/ExchangeRateUpdater.Core.Tests/CzechNationalBankExchangeRateProviderTests.cs

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+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using ExchangeRateUpdater.Core.ApiVendors;
+using ExchangeRateUpdater.Core.Models;
+using ExchangeRateUpdater.Core.Providers;
+using FluentAssertions;
+using Moq;
+using Xunit;
+
+namespace ExchangeRateUpdater.Core.Tests;
+
+public class CzechNationalBankExchangeRateProviderTests
+{
+    [Fact]
+    public async Task GetExchangeRates_EmptyInput_ReturnsEmpty_AndDoesNotCallVendor()
+    {
+        // Arrange
+        var vendorMock = new Mock<IExchangeRateVendor>(MockBehavior.Strict);
+        var sut = new CzechNationalBankExchangeRateProvider(vendorMock.Object);
+
+        // Act
+        var result = await sut.GetExchangeRates([]);
+
+        // Assert
+        result.Should().BeEmpty();
+        vendorMock.Verify(v => v.GetExchangeRates(It.IsAny<string>()), Times.Never);
+    }
+
+    [Fact]
+    public async Task GetExchangeRates_FiltersToRequestedCurrencies_AndCallsVendorOnce()
+    {
+        // Arrange
+        var vendorMock = new Mock<IExchangeRateVendor>();
+        vendorMock
+            .Setup(v => v.GetExchangeRates("CZK"))
+            .ReturnsAsync([
+                new(new Currency("CZK"), new Currency("USD"), 0.043m),
+                new(new Currency("CZK"), new Currency("EUR"), 0.039m),
+                new(new Currency("CZK"), new Currency("GBP"), 0.034m)
+            ]);
+
+        var sut = new CzechNationalBankExchangeRateProvider(vendorMock.Object);
+
+        var requested = new[] { new Currency("USD"), new Currency("EUR") };
+
+        // Act
+        var result = await sut.GetExchangeRates(requested);
+
+        // Assert
+        result.Should().HaveCount(2);
+        result.Select(r => r.TargetCurrency.ToString()).Should().BeEquivalentTo(new[] { "USD", "EUR" });
+        result.All(r => r.SourceCurrency.ToString() == "CZK").Should().BeTrue();
+        vendorMock.Verify(v => v.GetExchangeRates("CZK"), Times.Once);
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Core.Tests/ExchangeRateUpdater.Core.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
+    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Microsoft.Extensions.Configuration" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" Version="9.0.10" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.10" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\ExchangeRateUpdater.Core\ExchangeRateUpdater.Core.csproj" />
+  </ItemGroup>
+</Project>

jobs/Backend/Task/ExchangeRateUpdater.Core.Tests/ServiceConfigurationTests.cs

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+using System.Collections.Generic;
+using System.Linq;
+using ExchangeRateUpdater.Core.Configuration;
+using ExchangeRateUpdater.Core.Configuration.Options;
+using ExchangeRateUpdater.Core.Providers;
+using ExchangeRateUpdater.Core.Models;
+using FluentAssertions;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using Xunit;
+
+namespace ExchangeRateUpdater.Core.Tests;
+
+public class ServiceConfigurationTests
+{
+    [Fact]
+    public void AddCore_BindsCurrencies_AndRegistersProvider()
+    {
+        // Arrange
+        var inMemory = new[]
+        {
+            new KeyValuePair<string, string?>("Currencies:0", "usd"),
+            new KeyValuePair<string, string?>("Currencies:1", " EUR ")
+        };
+        var configuration = new ConfigurationBuilder().AddInMemoryCollection(inMemory).Build();
+        var services = new ServiceCollection();
+
+        services.AddSingleton(Moq.Mock.Of<ApiVendors.IExchangeRateVendor>());
+
+        // Act
+        services.AddCore(configuration);
+        var sp = services.BuildServiceProvider();
+
+        // Assert
+        sp.GetService<IExchangeRateProvider>().Should().NotBeNull();
+
+        var opts = sp.GetRequiredService<IOptions<CurrencyOptions>>().Value;
+        opts.Currencies.Should().HaveCount(2);
+        opts.Currencies.Select(c => c.ToString()).Should().BeEquivalentTo(new[] { "usd", " EUR " }.Select(s => new Currency(s).ToString()));
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Core/ApiVendors/IExchangeRateVendor.cs

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+using ExchangeRateUpdater.Core.Models;
+
+namespace ExchangeRateUpdater.Core.ApiVendors;
+
+public interface IExchangeRateVendor
+{
+    Task<List<ExchangeRate>> GetExchangeRates(string baseCurrencyCode);
+}

jobs/Backend/Task/ExchangeRateUpdater.Core/AppExceptions/VendorFailureException.cs

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+namespace ExchangeRateUpdater.Core.AppExceptions;
+
+public class VendorFailureException(string message) : Exception(message);

jobs/Backend/Task/ExchangeRateUpdater.Core/Configuration/Options/CurrencyOptions.cs

@@ -0,0 +1,8 @@
+using ExchangeRateUpdater.Core.Models;
+
+namespace ExchangeRateUpdater.Core.Configuration.Options;
+
+public class CurrencyOptions
+{
+    public Currency[] Currencies { get; set; } = [];
+}

jobs/Backend/Task/ExchangeRateUpdater.Core/Configuration/ServiceConfiguration.cs

@@ -0,0 +1,24 @@
+using ExchangeRateUpdater.Core.Configuration.Options;
+using ExchangeRateUpdater.Core.Models;
+using ExchangeRateUpdater.Core.Providers;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace ExchangeRateUpdater.Core.Configuration;
+
+public static class ServiceConfiguration
+{
+    public static IServiceCollection AddCore(this IServiceCollection services, IConfiguration configuration)
+    {
+        services.AddMemoryCache();
+        services.AddTransient<IExchangeRateProvider, CzechNationalBankExchangeRateProvider>();
+        services.AddOptions<CurrencyOptions>().Configure(opts =>
+            {
+                var currencies = configuration.GetSection("Currencies").Get<string[]>() ?? [];
+                opts.Currencies = currencies.Select(s => new Currency(s)).ToArray();
+            })
+            .ValidateOnStart();
+
+        return services;
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Core/ExchangeRateUpdater.Core.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net9.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <PackageReference Include="Microsoft.Extensions.Configuration.Abstractions" Version="9.0.10" />
+      <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="9.0.0" />
+      <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="9.0.0" />
+      <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="9.0.0" />
+    </ItemGroup>
+
+</Project>

jobs/Backend/Task/ExchangeRateUpdater.Core/Models/Currency.cs

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+namespace ExchangeRateUpdater.Core.Models;
+
+public class Currency(
+        string code
+    )
+{
+    /// <summary>
+    /// Three-letter ISO 4217 code of the currency.
+    /// </summary>
+    private string Code { get; } = code;
+
+    public override string ToString()
+    {
+        return Code;
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Core/Models/ExchangeRate.cs

@@ -0,0 +1,19 @@
+namespace ExchangeRateUpdater.Core.Models;
+
+    public class ExchangeRate(
+            Currency sourceCurrency,
+            Currency targetCurrency,
+            decimal value
+        )
+    {
+        public Currency SourceCurrency { get; } = sourceCurrency;
+
+        public Currency TargetCurrency { get; } = targetCurrency;
+
+        public decimal Value { get; } = value;
+
+        public override string ToString()
+        {
+            return $"{SourceCurrency}/{TargetCurrency}={Value}";
+        }
+    }

jobs/Backend/Task/ExchangeRateUpdater.Core/Providers/CzechNationalBankExchangeRateProvider.cs

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+using ExchangeRateUpdater.Core.ApiVendors;
+using ExchangeRateUpdater.Core.Models;
+using Microsoft.Extensions.Caching.Memory;
+
+namespace ExchangeRateUpdater.Core.Providers;
+
+public class CzechNationalBankExchangeRateProvider(
+        IExchangeRateVendor exchangeRateVendor,
+        IMemoryCache? cache = null
+    ) : IExchangeRateProvider
+{
+    private const string BaseCurrencyCode = "CZK";
+    private const string CacheKey = $"ExchangeRates:{BaseCurrencyCode}";
+    private readonly IMemoryCache _cache = cache ?? new MemoryCache(new MemoryCacheOptions());
+
+    public async Task<List<ExchangeRate>> GetExchangeRates(IEnumerable<Currency> currencies)
+    {
+        currencies = currencies.ToArray();
+        if (!currencies.Any()) return [];
+
+        var allRates = await _cache.GetOrCreateAsync(CacheKey, async entry =>
+        {
+            entry.AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(1);
+            return await exchangeRateVendor.GetExchangeRates(BaseCurrencyCode);
+        }) ?? [];
+
+        return allRates
+                .Where(rate => currencies.Any(currency => currency.ToString() == rate.TargetCurrency.ToString()))
+                .ToList();
+    }
+}

jobs/Backend/Task/ExchangeRateProvider.cs → jobs/Backend/Task/ExchangeRateUpdater.Core/Providers/ExchangeRateProvider.cs

@@ -1,19 +1,19 @@
 using System.Collections.Generic;
 using System.Linq;
+using ExchangeRateUpdater.Core.Models;
 
-namespace ExchangeRateUpdater
-{
-    public class ExchangeRateProvider
+namespace ExchangeRateUpdater.Core.Providers;
+    public class ExchangeRateProvider : IExchangeRateProvider
     {
         /// <summary>
         /// Should return exchange rates among the specified currencies that are defined by the source. But only those defined
         /// by the source, do not return calculated exchange rates. E.g. if the source contains "CZK/USD" but not "USD/CZK",
         /// do not return exchange rate "USD/CZK" with value calculated as 1 / "CZK/USD". If the source does not provide
         /// some of the currencies, ignore them.
         /// </summary>
-        public IEnumerable<ExchangeRate> GetExchangeRates(IEnumerable<Currency> currencies)
+        public Task<List<ExchangeRate>> GetExchangeRates(IEnumerable<Currency> currencies)
         {
-            return Enumerable.Empty<ExchangeRate>();
+            return Task.FromResult(new List<ExchangeRate>());
         }
     }
-}
+

jobs/Backend/Task/ExchangeRateUpdater.Core/Providers/IExchangeRateProvider.cs

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+using ExchangeRateUpdater.Core.Models;
+
+namespace ExchangeRateUpdater.Core.Providers;
+
+public interface IExchangeRateProvider
+{
+    Task<List<ExchangeRate>> GetExchangeRates(IEnumerable<Currency> currencies);
+}