Graeme Hedges - Backend Task (Exchange Rate Updater .NET)

.gitignore

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

jobs/Backend/Task/DTO/ExchangeRateDTO.cs

@@ -0,0 +1,15 @@
+using System.Text.Json.Serialization;
+
+namespace ExchangeRateUpdater.DTOs;
+
+public record ExchangeRateDTO
+{
+    [JsonPropertyName("amount")]
+    public int Amount { get; init; }
+
+    [JsonPropertyName("currencyCode")]
+    public string CurrencyCode { get; init; }
+
+    [JsonPropertyName("rate")]
+    public decimal Rate { get; init; }
+}

jobs/Backend/Task/DTO/ExchangeRatesDTO.cs

@@ -0,0 +1,9 @@
+using System.Text.Json.Serialization;
+
+namespace ExchangeRateUpdater.DTOs;
+
+public record ExchangeRatesDTO
+{
+    [JsonPropertyName("rates")]
+    public IEnumerable<ExchangeRateDTO> Rates { get; init; }
+}

jobs/Backend/Task/ExchangeRateUpdater.csproj

@@ -2,7 +2,14 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="9.0.1" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="9.0.1" />
+    <PackageReference Include="Microsoft.Extensions.Http" Version="9.0.1" />
+    <PackageReference Include="Microsoft.Extensions.Http.Resilience" Version="9.1.0" />
+  </ItemGroup>
+
 </Project>

jobs/Backend/Task/ExchangeRateUpdater.sln

@@ -1,22 +1,31 @@
-
-Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 14
-VisualStudioVersion = 14.0.25123.0
-MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ExchangeRateUpdater", "ExchangeRateUpdater.csproj", "{7B2695D6-D24C-4460-A58E-A10F08550CE0}"
-EndProject
-Global
-	GlobalSection(SolutionConfigurationPlatforms) = preSolution
-		Debug|Any CPU = Debug|Any CPU
-		Release|Any CPU = Release|Any CPU
-	EndGlobalSection
-	GlobalSection(ProjectConfigurationPlatforms) = postSolution
-		{7B2695D6-D24C-4460-A58E-A10F08550CE0}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{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
-	EndGlobalSection
-	GlobalSection(SolutionProperties) = preSolution
-		HideSolutionNode = FALSE
-	EndGlobalSection
-EndGlobal
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.8.34309.116
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ExchangeRateUpdater", "ExchangeRateUpdater.csproj", "{7B2695D6-D24C-4460-A58E-A10F08550CE0}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ExchangeRateUpdater.Tests", "..\TestExchangeRateUpdater.Tests\ExchangeRateUpdater.Tests.csproj", "{D7EC3579-D063-4F8C-B3D3-5D1B6B287BE2}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{7B2695D6-D24C-4460-A58E-A10F08550CE0}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{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
+		{D7EC3579-D063-4F8C-B3D3-5D1B6B287BE2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D7EC3579-D063-4F8C-B3D3-5D1B6B287BE2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D7EC3579-D063-4F8C-B3D3-5D1B6B287BE2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D7EC3579-D063-4F8C-B3D3-5D1B6B287BE2}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {26DF4BBA-AE0E-4E97-B657-B6406E4C09F2}
+	EndGlobalSection
+EndGlobal

jobs/Backend/Task/GlobalUsings.cs

@@ -0,0 +1 @@
+global using System.Collections.Generic;

jobs/Backend/Task/Models/Currency.cs

@@ -0,0 +1,19 @@
+namespace ExchangeRateUpdater.Models;
+
+public class Currency
+{
+    public Currency(string code)
+    {
+        Code = code;
+    }
+
+    /// <summary>
+    /// Three-letter ISO 4217 code of the currency.
+    /// </summary>
+    public string Code { get; }
+
+    public override string ToString()
+    {
+        return Code;
+    }
+}

jobs/Backend/Task/Models/ExchangeRate.cs

@@ -0,0 +1,22 @@
+namespace ExchangeRateUpdater.Models;
+
+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; }
+
+    public decimal Value { get; }
+
+    public override string ToString()
+    {
+        return $"{SourceCurrency}/{TargetCurrency}={Value}";
+    }
+}

jobs/Backend/Task/Program.cs

@@ -1,43 +1,86 @@
-using System;
-using System.Collections.Generic;
+using ExchangeRateUpdater.Models;
+using ExchangeRateUpdater.Providers;
+using ExchangeRateUpdater.Services;
+using Microsoft.Extensions.Caching.Memory;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using System;
 using System.Linq;
 
-namespace ExchangeRateUpdater
+var host = new HostBuilder()
+    .ConfigureServices(services =>
+    {
+        services.AddHttpClient<IExchangeRateService, ExchangeRateService>(
+            client => 
+            {
+                client.BaseAddress = new Uri("https://api.cnb.cz/cnbapi/");
+            })
+            .AddStandardResilienceHandler();
+        services.AddTransient<IExchangeRateProvider, ExchangeRateProvider>();
+        services.AddSingleton(TimeProvider.System);
+        services.AddSingleton<IMemoryCache, MemoryCache>();
+        services.AddLogging();
+    })
+    .ConfigureLogging(logging =>
+    {
+        logging.AddConsole();
+    })
+    .Build();
+
+var exchangeRateProvider = host.Services.GetRequiredService<IExchangeRateProvider>();
+
+IEnumerable<Currency> currencies = new[]
+{
+    new Currency("USD"),
+    new Currency("EUR"),
+    new Currency("CZK"),
+    new Currency("JPY"),
+    new Currency("KES"),
+    new Currency("RUB"),
+    new Currency("THB"),
+    new Currency("TRY"),
+    new Currency("XYZ")
+};
+
+while (true)
 {
-    public static class Program
+    try
     {
-        private static IEnumerable<Currency> currencies = new[]
-        {
-            new Currency("USD"),
-            new Currency("EUR"),
-            new Currency("CZK"),
-            new Currency("JPY"),
-            new Currency("KES"),
-            new Currency("RUB"),
-            new Currency("THB"),
-            new Currency("TRY"),
-            new Currency("XYZ")
-        };
+        var rates = await exchangeRateProvider.GetExchangeRates(currencies);
 
-        public static void Main(string[] args)
-        {
-            try
-            {
-                var provider = new ExchangeRateProvider();
-                var rates = provider.GetExchangeRates(currencies);
+        if (!rates.Any())
+        {
+            Console.WriteLine(string.Empty);
+            Console.WriteLine("No exchange rates found for the chosen currencies.");
+            Console.WriteLine(string.Empty);
+            Console.WriteLine("Press any key to retry...");
+            Console.ReadKey();
+            Console.Clear();
+            continue;
+        }
 
-                Console.WriteLine($"Successfully retrieved {rates.Count()} exchange rates:");
-                foreach (var rate in rates)
-                {
-                    Console.WriteLine(rate.ToString());
-                }
-            }
-            catch (Exception e)
-            {
-                Console.WriteLine($"Could not retrieve exchange rates: '{e.Message}'.");
-            }
+        Console.WriteLine(string.Empty);
+        Console.WriteLine($"Successfully retrieved {rates.Count()} exchange rates:");
+        Console.WriteLine(string.Empty);
 
-            Console.ReadLine();
+        foreach (var rate in rates)
+        {
+            Console.WriteLine(rate.ToString());
+            Console.WriteLine(string.Empty);
         }
+
+        Console.WriteLine("Press any key to refresh...");
+        Console.ReadKey();
+        Console.Clear();
+    }
+    catch (Exception e)
+    {
+        Console.WriteLine(string.Empty);
+        Console.WriteLine($"Could not retrieve exchange rates: '{e.Message}'.");
+        Console.WriteLine(string.Empty);
+        Console.WriteLine("Press any key to retry...");
+        Console.ReadKey();
+        Console.Clear();
     }
-}
+}

jobs/Backend/Task/Providers/ExchangeRateProvider.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection.Metadata.Ecma335;
+using System.Threading.Tasks;
+using ExchangeRateUpdater.DTOs;
+using ExchangeRateUpdater.Models;
+using ExchangeRateUpdater.Services;
+using Microsoft.Extensions.Logging;
+
+namespace ExchangeRateUpdater.Providers;
+
+public class ExchangeRateProvider : IExchangeRateProvider
+{
+    private readonly IExchangeRateService _exchangeRateService;
+    private readonly ILogger<ExchangeRateProvider> _logger;
+
+    public ExchangeRateProvider(IExchangeRateService exchangeRateService, ILogger<ExchangeRateProvider> logger)
+    {
+        _exchangeRateService = exchangeRateService;
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    public async Task<IEnumerable<ExchangeRate>> GetExchangeRates(IEnumerable<Currency> currencies)
+    {
+        var exchangeRates = await _exchangeRateService.GetExchangeRatesAsync();
+
+        var filteredRates = exchangeRates.Rates
+            .Where(rate =>
+                currencies.Any(currency => currency.Code == rate.CurrencyCode))
+            .Select(rate =>
+                new ExchangeRate(new Currency(rate.CurrencyCode), new Currency("CZK"), rate.Rate / rate.Amount));
+
+        if (filteredRates.Count() is 0)
+        {
+            _logger.LogInformation("No matching rates found for chosen currency codes");
+        }
+
+        return filteredRates;
+    }
+}

jobs/Backend/Task/Providers/IExchangeRateProvider.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+using ExchangeRateUpdater.Models;
+
+namespace ExchangeRateUpdater.Providers;
+
+public interface 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>
+    Task<IEnumerable<ExchangeRate>> GetExchangeRates(IEnumerable<Currency> currencies);
+}