Exchange Rate Provider - Alberto Salas Hernandez

.gitignore

@@ -21,3 +21,4 @@
 node_modules
 bower_components
 npm-debug.log
+/.vs

jobs/Backend/ExchangeRateUpdater.Test/CurrencyTest.cs

@@ -0,0 +1,27 @@
+namespace ExchangeRateUpdater.Test;
+
+public class CurrencyTest
+{
+    [Fact]
+    public void Currency_RecordValueComparison_ReturnsTrueForEqualCurrencies()
+    {
+        var symbol = "USD";
+        var currency1 = new Currency(symbol);
+        var currency2 = new Currency(symbol);
+
+        var result = currency1.Equals(currency2);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public void Currency_RecordValueComparison_ReturnsFalseForDifferentCurrencies()
+    {
+        var currency1 = new Currency("USD");
+        var currency2 = new Currency("EUR");
+
+        var result = currency1.Equals(currency2);
+
+        Assert.False(result);
+    }
+}

jobs/Backend/ExchangeRateUpdater.Test/ExchangeRateProviderTest.cs

@@ -0,0 +1,107 @@
+using ExchangeRateUpdater.Contracts;
+using ExchangeRateUpdater.Providers.CNB;
+using Microsoft.Extensions.Caching.Memory;
+using Microsoft.Extensions.Options;
+using Moq;
+
+namespace ExchangeRateUpdater.Test;
+
+public class ExchangeRateProviderTest
+{
+    [Fact]
+    public async Task GetExchangeRatesAsync_UsesCache_WhenCalledTwice()
+    {
+        // Arrange
+        var targetDate = DateOnly.FromDateTime(DateTime.UtcNow);
+        var expectedCacheKey = $"{nameof(CNBCurrencyExchangeProvider)}_{targetDate:yyyy-MM-dd}";
+
+        var options = Options.Create(new CNBExchangeRateProviderOptions
+        {
+            Name = "CNB",
+            BaseUrl = "https://api.cnb.cz",
+            CacheAbsoluteExpiration = TimeSpan.FromMinutes(10),
+            CacheSlidingExpiration = TimeSpan.FromMinutes(2)
+        });
+
+        var apiRates = new List<ExchangeRate>
+        {
+            new(new Currency("EUR"), new Currency("CZK"), 25.10m),
+            new(new Currency("USD"), new Currency("CZK"), 23.40m)
+        };
+
+        var clientMock = new Mock<ICNBExchangeRateApiClient>(MockBehavior.Strict);
+        clientMock
+            .Setup(x => x.FetchExchangeRatesAsync(
+                It.Is<DateOnly>(d => d == targetDate),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(apiRates);
+
+        var cacheMock = new Mock<IMemoryCache>(MockBehavior.Strict);
+
+        var callCount = 0;
+
+        object? cachedObject = null;
+
+        cacheMock
+            .Setup(c => c.TryGetValue(It.IsAny<object>(), out cachedObject))
+            .Returns((object key, out object? value) =>
+            {
+                Assert.Equal(expectedCacheKey, key);
+
+                callCount++;
+
+                if (callCount == 1)
+                {
+                    value = null;
+                    return false;
+                }
+
+                value = apiRates;
+                return true;
+            });
+
+        // Because _cache.Set(...) is an extension method, it calls CreateEntry internally.
+        var entryMock = new Mock<ICacheEntry>();
+
+        cacheMock
+            .Setup(c => c.CreateEntry(It.Is<object>(k => k.Equals(expectedCacheKey))))
+            .Returns(entryMock.Object);
+
+        // The Set extension will set Value and Expiration properties and then dispose the entry.
+        entryMock.SetupAllProperties();
+        entryMock.Setup(e => e.Dispose());
+
+        var sut = new CNBCurrencyExchangeProvider(clientMock.Object, cacheMock.Object, options);
+
+        var requestedCurrencies = new[] { new Currency("EUR") };
+
+        // Act
+
+        // cache miss
+        var first = (await sut.GetExchangeRatesAsync(requestedCurrencies)).ToList();
+
+        // cache hit
+        var second = (await sut.GetExchangeRatesAsync(requestedCurrencies)).ToList();
+
+        Assert.Single(first);
+        Assert.Single(second);
+        Assert.Equal("EUR", first[0].SourceCurrency.Code);
+        Assert.Equal("EUR", second[0].SourceCurrency.Code);
+
+        // Assert
+
+        // client called only once
+        clientMock.Verify(x => x.FetchExchangeRatesAsync(
+                It.Is<DateOnly>(d => d == targetDate),
+                It.IsAny<CancellationToken>()),
+            Times.Once);
+
+        // cache was written only once
+        cacheMock.Verify(c => c.CreateEntry(It.Is<object>(k => k.Equals(expectedCacheKey))), Times.Once);
+        entryMock.VerifySet(e => e.Value = It.IsAny<object>(), Times.Once);
+        entryMock.Verify(e => e.Dispose(), Times.Once);
+
+        // TryGetValue called twice
+        cacheMock.Verify(c => c.TryGetValue(It.IsAny<object>(), out cachedObject), Times.Exactly(2));
+    }
+}

jobs/Backend/ExchangeRateUpdater.Test/ExchangeRateUpdater.Test.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="xunit" Version="2.5.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Task\ExchangeRateUpdater.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+</Project>

jobs/Backend/Task/.gitignore

@@ -0,0 +1,21 @@
+!.gitkeep
+!.gitignore
+!*.dll
+[Oo]bj
+[Bb]in
+*.user
+*.suo
+*.[Cc]ache
+*.bak
+*.ncb
+*.DS_Store
+*.userprefs
+*.iml
+*.ncrunch*
+.*crunch*.local.xml
+.idea
+[Tt]humbs.db
+*.tgz
+*.sublime-*
+
+.vs/

jobs/Backend/Task/Constants.cs

@@ -0,0 +1,6 @@
+namespace ExchangeRateUpdater;
+
+public static class Constants
+{
+    public const string CNBExchangeRateProviderName = "CNBExchangeRateProvider";
+}

jobs/Backend/Task/Contracts/ICNBExchangeRateApiClient.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace ExchangeRateUpdater.Contracts;
+
+public interface ICNBExchangeRateApiClient
+{
+    Task<IEnumerable<ExchangeRate>> FetchExchangeRatesAsync(DateOnly date, CancellationToken ct = default);
+}

jobs/Backend/Task/Contracts/IExchangeRateProvider.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace ExchangeRateUpdater.Contracts;
+
+public interface IExchangeRateProvider
+{
+    /// <summary>
+    /// Returns exchange rates among the specified currencies that are defined by the source. But only those defined
+    /// by the source. It does not return calculated exchange rates. E.g. if the source contains "CZK/USD" but not "USD/CZK",
+    /// it does not return exchange rate "USD/CZK" with value calculated as 1 / "CZK/USD". If the source does not provide
+    /// some of the currencies, it will be ignored.
+    /// </summary>
+    /// <param name="currencies">Source currencies whose exchange rate is needed.</param>
+    /// <param name="date">The date for which exchange rates are requested (null for the latest rates).</param>
+    /// <returns>
+    /// Returns a collection of ExchangeRate objects containing the requested information.
+    /// </returns>
+    Task<IEnumerable<ExchangeRate>> GetExchangeRatesAsync(IEnumerable<Currency> currencies);
+}

jobs/Backend/Task/Currency.cs

@@ -1,20 +1,19 @@
-namespace ExchangeRateUpdater
+namespace ExchangeRateUpdater;
+
+public sealed record Currency
 {
-    public class Currency
+    public Currency(string code)
     {
-        public Currency(string code)
-        {
-            Code = code;
-        }
+        Code = code.ToUpperInvariant();
+    }
 
-        /// <summary>
-        /// Three-letter ISO 4217 code of the currency.
-        /// </summary>
-        public string Code { get; }
+    /// <summary>
+    /// Three-letter ISO 4217 code of the currency.
+    /// </summary>
+    public string Code { get; }
 
-        public override string ToString()
-        {
-            return Code;
-        }
+    public override string ToString()
+    {
+        return Code;
     }
 }

jobs/Backend/Task/Exceptions/ExchangeRateProviderException.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace ExchangeRateUpdater.Exceptions;
+
+public sealed class ExchangeRateProviderException : Exception
+{
+    public ExchangeRateProviderException(string message)
+        : base(message)
+    {
+    }
+
+    public ExchangeRateProviderException(string message, Exception innerException)
+        : base(message, innerException)
+    {
+    }
+}

jobs/Backend/Task/ExchangeRate.cs

@@ -1,23 +1,22 @@
-namespace ExchangeRateUpdater
+namespace ExchangeRateUpdater;
+
+public class ExchangeRate
 {
-    public class ExchangeRate
+    public ExchangeRate(Currency sourceCurrency, Currency targetCurrency, decimal value)
     {
-        public ExchangeRate(Currency sourceCurrency, Currency targetCurrency, decimal value)
-        {
-            SourceCurrency = sourceCurrency;
-            TargetCurrency = targetCurrency;
-            Value = value;
-        }
+        SourceCurrency = sourceCurrency;
+        TargetCurrency = targetCurrency;
+        Value = value;
+    }
 
-        public Currency SourceCurrency { get; }
+    public Currency SourceCurrency { get; }
 
-        public Currency TargetCurrency { get; }
+    public Currency TargetCurrency { get; }
 
-        public decimal Value { get; }
+    public decimal Value { get; }
 
-        public override string ToString()
-        {
-            return $"{SourceCurrency}/{TargetCurrency}={Value}";
-        }
+    public override string ToString()
+    {
+        return $"{SourceCurrency}/{TargetCurrency}={Value}";
     }
 }

jobs/Backend/Task/ExchangeRateUpdater.csproj

@@ -2,7 +2,25 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Caching.Abstractions" Version="10.0.2" />
+    <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="10.0.2" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" Version="10.0.2" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="10.0.2" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="10.0.2" />
+    <PackageReference Include="Microsoft.Extensions.Http" Version="10.0.2" />
+    <PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="10.2.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.2" />
+    <PackageReference Include="Polly" Version="8.6.5" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="appsettings.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </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 = 17.14.36429.23 d17.14
 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.Test", "..\ExchangeRateUpdater.Test\ExchangeRateUpdater.Test.csproj", "{4F7B57E4-E166-4E4B-8EE8-3C7EF0729606}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -15,6 +17,10 @@ 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
+		{4F7B57E4-E166-4E4B-8EE8-3C7EF0729606}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4F7B57E4-E166-4E4B-8EE8-3C7EF0729606}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4F7B57E4-E166-4E4B-8EE8-3C7EF0729606}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4F7B57E4-E166-4E4B-8EE8-3C7EF0729606}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE