CNB Exchange Rate Provider implementation and documentation

jobs/Backend/Task/.vs/ExchangeRateUpdater/xs/UserPrefs.xml

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+  <MonoDevelop.Ide.Workbench ActiveDocument="Program.cs">
+    <Files>
+      <File FileName="../../../../../../usr/local/share/dotnet/sdk/7.0.317/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.TargetFrameworkInference.targets" Line="148" Column="43" IsPinned="True" />
+      <File FileName="Program.cs" Line="1" Column="1" />
+      <File FileName="Config/AppConfig.cs" />
+      <File FileName="Models/Currency.cs" />
+      <File FileName="Models/ExchangeRate.cs" />
+      <File FileName="Services/CnbClient.cs" />
+      <File FileName="Services/CnbParser.cs" />
+      <File FileName="Services/ExchangeRateProvider.cs" />
+      <File FileName="appsettings.json" />
+    </Files>
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+  </MonoDevelop.Ide.Workbench>
+  <MonoDevelop.Ide.ItemProperties.ExchangeRateUpdater PreferredExecutionTarget="MonoDevelop.Default" />
+  <MonoDevelop.Ide.DebuggingService.PinnedWatches />
+  <MultiItemStartupConfigurations />
+  <MonoDevelop.Ide.Workspace ActiveConfiguration="Debug" />
+  <MonoDevelop.Ide.DebuggingService.Breakpoints>
+    <BreakpointStore />
+  </MonoDevelop.Ide.DebuggingService.Breakpoints>
+</Properties>

jobs/Backend/Task/.vs/ExchangeRateUpdater/xs/project-cache/ExchangeRateUpdater-Debug.json

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jobs/Backend/Task/Config/AppConfig.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+
+namespace ExchangeRateUpdater.Config;
+
+public sealed class AppConfig
+{
+    public ExchangeRateSettings ExchangeRateSettings { get; init; } = new();
+}
+
+public sealed class ExchangeRateSettings
+{
+    [Required] public Uri CnbDailyUrl { get; init; } = default!;
+    [Range(1, 120)] public int HttpTimeoutSeconds { get; init; } = 10;
+    public List<string> Currencies { get; init; } = new();
+}

jobs/Backend/Task/ExchangeRateUpdater.csproj

@@ -2,7 +2,37 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+      <PackageReference Include="Microsoft.Extensions.Hosting" Version="9.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="9.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Options.DataAnnotations" Version="9.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="9.0.0" />
+
+    <!-- HttpClientFactory -->
+    <PackageReference Include="Microsoft.Extensions.Http" Version="9.0.0" />
+
+    <!-- In-memory cache (patched) -->
+    <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="9.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="appsettings.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+
+  <ItemGroup>
+    <None Remove="Models\" />
+    <None Remove="Services\" />
+    <None Remove="Config\" />
+  </ItemGroup>
+  <ItemGroup>
+    <Folder Include="Models\" />
+    <Folder Include="Services\" />
+    <Folder Include="Config\" />
+  </ItemGroup>
 </Project>

jobs/Backend/Task/Models/Currency.cs

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+namespace ExchangeRateUpdater;
+
+public sealed record Currency(string Code)
+{
+    public override string ToString() => Code;
+}

jobs/Backend/Task/Models/ExchangeRate.cs

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+namespace ExchangeRateUpdater;
+
+public sealed record ExchangeRate(Currency SourceCurrency, Currency TargetCurrency, decimal Value)
+{
+    public override string ToString() => $"{SourceCurrency}/{TargetCurrency}={Value}";
+}

jobs/Backend/Task/Program.cs

@@ -1,43 +1,85 @@
 using System;
-using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
+using ExchangeRateUpdater;
+using ExchangeRateUpdater.Config;
+using ExchangeRateUpdater.Services;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 
-namespace ExchangeRateUpdater
-{
-    public static class Program
+var host = Host.CreateDefaultBuilder(args)
+    .ConfigureAppConfiguration(cfg =>
+    {
+        cfg.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
+           .AddEnvironmentVariables();
+    })
+    .ConfigureServices((context, services) =>
     {
-        private static IEnumerable<Currency> currencies = new[]
+        var configuration = context.Configuration;
+
+        services.AddOptions<ExchangeRateSettings>()
+                .Bind(configuration.GetSection("ExchangeRateSettings"))
+                .ValidateDataAnnotations()
+                .Validate(s => s.CnbDailyUrl is not null && s.CnbDailyUrl.IsAbsoluteUri, "CnbDailyUrl must be absolute")
+                .Validate(s => s.CnbDailyUrl.Scheme == Uri.UriSchemeHttps, "CnbDailyUrl must be HTTPS")
+                .ValidateOnStart();
+
+        services.AddMemoryCache();
+
+        services.AddHttpClient<ICnbClient, CnbClient>((sp, client) =>
         {
-            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")
-        };
-
-        public static void Main(string[] args)
+            var s = sp.GetRequiredService<IOptions<ExchangeRateSettings>>().Value;
+            client.Timeout = TimeSpan.FromSeconds(s.HttpTimeoutSeconds);
+            client.DefaultRequestHeaders.UserAgent.ParseAdd("ExchangeRateUpdater/1.0");
+            client.DefaultRequestHeaders.Accept.ParseAdd("text/plain");
+            client.BaseAddress = s.CnbDailyUrl; 
+        });
+
+        services.AddSingleton<ICnbParser, CnbParser>();
+        services.AddSingleton<IExchangeRateProvider, ExchangeRateProvider>();
+    })
+    .ConfigureLogging(logging =>
+    {
+        logging.ClearProviders();
+        logging.AddConsole();
+    })
+    .Build();
+
+using var scope = host.Services.CreateScope();
+var sp = scope.ServiceProvider;
+var logger = sp.GetRequiredService<ILogger<Program>>();
+
+try
+{
+    var settings  = sp.GetRequiredService<IOptions<ExchangeRateSettings>>().Value;
+    var client    = sp.GetRequiredService<ICnbClient>();
+    var provider  = sp.GetRequiredService<IExchangeRateProvider>();
+
+    // Fetch payload once to detect decimal style used by the TXT feed.
+    var payload       = await client.GetDailyRatesAsync(default);
+    var outputCulture = CnbParser.DetectCulture(payload); 
+
+    // 2) currencies from config.
+    var currencies = settings.Currencies.Select(c => new Currency(c.Trim())).ToArray();
+    if (currencies.Length == 0)
+    {
+        logger.LogWarning("No currencies configured in appsettings.json.");
+    }
+    else
+    {
+        // Get per-unit rates and print with detected culture.
+        var rates = await provider.GetExchangeRatesAsync(currencies, default);
+        foreach (var r in rates)
         {
-            try
-            {
-                var provider = new ExchangeRateProvider();
-                var rates = provider.GetExchangeRates(currencies);
-
-                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.ReadLine();
+            var formatted = r.Value.ToString("0.######", outputCulture);
+            Console.WriteLine($"{r.SourceCurrency}/{r.TargetCurrency}={formatted}");
         }
     }
 }
+catch (Exception ex)
+{
+    logger.LogError(ex, "An error occurred while fetching exchange rates.");
+}

jobs/Backend/Task/Readme.md

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+# Exchange Rate Updater (CNB Provider)
+
+This is a .NET 8 console application that fetches daily exchange rates from the **Czech National Bank (CNB)** and prints the configured currency rates against CZK.
+
+---
+
+## 🚀 Features
+
+- Fetches **real CNB daily rates** from official `.txt` feed.
+- Automatically detects **decimal separator style** (`,` or `.`) from the file.
+- Parses and computes **per-unit exchange rates** (`rate / amount`).
+- Supports configurable currencies, timeout, and URL.
+- Caches parsed data for faster repeated runs.
+- Implements DI, logging, and options validation for production use.
+
+---
+
+## ⚙️ Configuration
+
+All settings are defined in `appsettings.json`:
+
+```json
+{
+  "ExchangeRateSettings": {
+    "CnbDailyUrl": "https://www.cnb.cz/en/financial-markets/foreign-exchange-market/central-bank-exchange-rate-fixing/central-bank-exchange-rate-fixing/daily.txt",
+    "HttpTimeoutSeconds": 10,
+    "Currencies": [ "EUR", "USD", "GBP", "INR" ]
+  }
+}

jobs/Backend/Task/Services/CnbClient.cs

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+using System;
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+using ExchangeRateUpdater.Config;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace ExchangeRateUpdater.Services;
+
+public sealed class CnbClient : ICnbClient
+{
+    private readonly HttpClient _http;
+    private readonly ExchangeRateSettings _settings;
+    private readonly ILogger<CnbClient> _logger;
+
+    public CnbClient(HttpClient http, IOptions<ExchangeRateSettings> options, ILogger<CnbClient> logger)
+    {
+        _http = http;
+        _settings = options.Value;
+        _logger = logger;
+    }
+
+    public async Task<string> GetDailyRatesAsync(CancellationToken ct)
+    {
+        try
+        {
+            using var resp = await _http.GetAsync("", HttpCompletionOption.ResponseHeadersRead, ct);
+            resp.EnsureSuccessStatusCode();
+            return await resp.Content.ReadAsStringAsync(ct);
+        }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested)
+        {
+            _logger.LogWarning("Fetching CNB daily rates was canceled.");
+            throw;
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "HTTP error fetching CNB daily rates from {Url}", _settings.CnbDailyUrl);
+            throw;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to fetch CNB daily rates from {Url}", _settings.CnbDailyUrl);
+            throw;
+        }
+    }
+}