Ammar Fouda - .Net Rate Exchange Task

.gitignore

@@ -21,3 +21,9 @@
 node_modules
 bower_components
 npm-debug.log
+/jobs/Backend/Task/.vs/ExchangeRateUpdater
+/jobs/Backend/Task/.vs/ProjectEvaluation
+/jobs/Backend/Task/.dockerignore
+/jobs/Backend/Task/Dockerfile
+/jobs/Backend/Task/EXCEPTION_HANDLING.md
+/jobs/Backend/Task/README.md

jobs/Backend/Task/Application/Interfaces/IExchangeRateService.cs

@@ -0,0 +1,19 @@
+using ExchangeRateUpdater.Domain;
+
+namespace ExchangeRateUpdater.Application.Interfaces
+{
+    /// <summary>
+    /// Application service interface for retrieving exchange rates.
+    /// Orchestrates multiple exchange rate providers.
+    /// </summary>
+    public interface IExchangeRateService
+    {
+        /// <summary>
+        /// Retrieves exchange rates for the requested currencies asynchronously.
+        /// Only returns rates explicitly provided by the underlying providers.
+        /// </summary>
+        /// <param name="requestedCurrencies">Currencies to fetch rates for.</param>
+        /// <returns>Collection of exchange rates.</returns>
+        Task<IEnumerable<ExchangeRate>> GetRatesAsync(IEnumerable<Currency> requestedCurrencies);
+    }
+}

jobs/Backend/Task/Application/Services/ExchangeRateService.cs

@@ -0,0 +1,57 @@
+using ExchangeRateUpdater.Application.Interfaces;
+using ExchangeRateUpdater.Domain;
+
+namespace ExchangeRateUpdater.Application.Services
+{
+    /// <summary>
+    /// Application service to orchestrate exchange rate retrieval.
+    /// Uses one or more IExchangeRateProvider instances.
+    /// </summary>
+    public class ExchangeRateService : IExchangeRateService
+    {
+        private readonly IEnumerable<IExchangeRateProvider> _providers;
+        private readonly ILogger<ExchangeRateService> _logger;
+
+        /// <summary>
+        /// Initializes the service with one or more exchange rate providers.
+        /// </summary>
+        /// <param name="providers">Injected exchange rate providers.</param>
+        public ExchangeRateService(IEnumerable<IExchangeRateProvider> providers, ILogger<ExchangeRateService> logger)
+        {
+            _providers = providers ?? throw new ArgumentNullException(nameof(providers));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        }
+
+        /// <summary>
+        /// Retrieves exchange rates for the requested currencies asynchronously.
+        /// Only returns rates explicitly provided by the underlying providers.
+        /// </summary>
+        public Task<IEnumerable<ExchangeRate>> GetRatesAsync(IEnumerable<Currency> requestedCurrencies)
+        {
+            if (requestedCurrencies == null)
+                throw new ArgumentNullException(nameof(requestedCurrencies));
+
+            var results = new List<ExchangeRate>();
+
+            foreach (var provider in _providers)
+            {
+                try
+                {
+                    var rates = provider.GetExchangeRates(requestedCurrencies);
+                    if (rates != null)
+                        results.AddRange(rates);
+                }
+                catch (Exception ex) { 
+                    _logger.LogError(ex, "Exchange rate provider '{Provider}' failed.", provider.GetType().Name);
+                    throw new InvalidOperationException(
+                        $"Failed to retrieve exchange rates from provider '{provider.GetType().Name}'.", ex);
+                }
+            }
+            var distinctRates = results
+                .GroupBy(r => new { SourceCode= r.Source.Code, TargetCode = r.Target.Code })
+                .Select(g => g.First());
+
+            return Task.FromResult(distinctRates.AsEnumerable());
+        }
+    }
+}

jobs/Backend/Task/Currency.cs → jobs/Backend/Task/Domain/Currency.cs

@@ -1,4 +1,4 @@
-namespace ExchangeRateUpdater
+namespace ExchangeRateUpdater.Domain
 {
     public class Currency
     {

jobs/Backend/Task/Domain/ExchangeRate.cs

@@ -0,0 +1,37 @@
+namespace ExchangeRateUpdater.Domain
+{
+    /// <summary>
+    /// Represents an exchange rate between two currencies.
+    /// Immutable and validated.
+    /// </summary>
+    public class ExchangeRate
+    {
+        /// <summary>
+        /// Source currency of the exchange rate.
+        /// </summary>
+        public Currency Source { get; }
+
+        /// <summary>
+        /// Target currency of the exchange rate.
+        /// </summary>
+        public Currency Target { get; }
+
+        /// <summary>
+        /// Exchange rate value (e.g., 1 USD = 23.5 CZK -> Value = 23.5).
+        /// </summary>
+        public decimal Value { get; }
+
+        /// <summary>
+        /// Creates a new ExchangeRate instance.
+        /// </summary>
+        /// <param name="source">Source currency (required).</param>
+        /// <param name="target">Target currency (required).</param>
+        /// <param name="value">Exchange rate value.</param>
+        public ExchangeRate(Currency source, Currency target, decimal value)
+        {
+            Source = source ?? throw new ArgumentNullException(nameof(source));
+            Target = target ?? throw new ArgumentNullException(nameof(target));
+            Value = value;
+        }
+    }
+}

jobs/Backend/Task/Domain/IExchangeRateProvider.cs

@@ -0,0 +1,18 @@
+namespace ExchangeRateUpdater.Domain
+{
+    /// <summary>
+    /// Defines a contract for exchange rate providers.
+    /// Returns only explicitly defined rates from the source.
+    /// </summary>
+    public interface IExchangeRateProvider
+    {
+        /// <summary>
+        /// Returns exchange rates for the requested currencies.
+        /// Only returns rates explicitly defined by the source, 
+        /// does not calculate inverted rates.
+        /// </summary>
+        /// <param name="requestedCurrencies">Currencies to retrieve rates for.</param>
+        /// <returns>Collection of exchange rates.</returns>
+        IEnumerable<ExchangeRate> GetExchangeRates(IEnumerable<Currency> requestedCurrencies);
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.csproj

@@ -1,8 +1,53 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
+	  <ImplicitUsings>enable</ImplicitUsings>
+	  <Nullable>enable</Nullable>
+    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
+	  <GenerateDocumentationFile>false</GenerateDocumentationFile>
+	  <DockerDefaultTargetOS>Windows</DockerDefaultTargetOS>
+	  <DockerfileContext>.</DockerfileContext>
   </PropertyGroup>
 
+  <ItemGroup>
+    <Compile Remove="Tests\ExchangeRateUpdater.Tests\bin\**" />
+    <Compile Remove="Tests\ExchangeRateUpdater.Tests\obj\**" />
+    <Content Remove="Tests\ExchangeRateUpdater.Tests\bin\**" />
+    <Content Remove="Tests\ExchangeRateUpdater.Tests\obj\**" />
+    <EmbeddedResource Remove="Tests\ExchangeRateUpdater.Tests\bin\**" />
+    <EmbeddedResource Remove="Tests\ExchangeRateUpdater.Tests\obj\**" />
+    <None Remove="Tests\ExchangeRateUpdater.Tests\bin\**" />
+    <None Remove="Tests\ExchangeRateUpdater.Tests\obj\**" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="DotNetEnv" Version="3.1.1" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="10.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" Version="10.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <EditorConfigFiles Remove="E:\Projects\developers\jobs\Backend\Task\.editorconfig" />
+  </ItemGroup>
+
+  <ItemGroup>
+		<PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.22.1" />
+		<PackageReference Include="Swashbuckle.AspNetCore" Version="6.5.0" />
+		<PackageReference Include="xunit.assert" Version="2.6.2" />
+		<PackageReference Include="xunit.extensibility.core" Version="2.9.3" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="appsettings.development.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+    <None Update="appsettings.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+    <None Update="appsettings.production.json">
+      <CopyToOutputDirectory>PreserveNewest</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 = 17.14.36121.58 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.Tests", "Tests\ExchangeRateUpdater.Tests\ExchangeRateUpdater.Tests.csproj", "{D3F6F8E4-8A7F-4B2C-94A2-0D9B6A2E2B10}"
+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
+		{D3F6F8E4-8A7F-4B2C-94A2-0D9B6A2E2B10}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D3F6F8E4-8A7F-4B2C-94A2-0D9B6A2E2B10}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D3F6F8E4-8A7F-4B2C-94A2-0D9B6A2E2B10}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D3F6F8E4-8A7F-4B2C-94A2-0D9B6A2E2B10}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {F71216DE-D6B5-4542-B482-F54372660740}
+	EndGlobalSection
 EndGlobal

jobs/Backend/Task/Infrastructure/Sources/CnbExchangeRateProvider.cs

@@ -0,0 +1,114 @@
+using ExchangeRateUpdater.Domain;
+using System.Globalization;
+
+namespace ExchangeRateUpdater.Infrastructure.Sources
+{
+    public class CnbExchangeRateProvider : IExchangeRateProvider
+    {
+        private const int HttpTimeoutSeconds = 10;
+        private const string TargetCurrency = "CZK";
+        private readonly List<string> _endpoints = new();
+        private readonly ILogger<CnbExchangeRateProvider> _logger;
+
+		public CnbExchangeRateProvider(IConfiguration configuration, ILogger<CnbExchangeRateProvider> logger)
+        {
+			_endpoints.Add(configuration["ExchangeRateApi:exchangeRateEN"]);
+			_endpoints.Add(configuration["ExchangeRateApi:exchangeRateSC"]);
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+		}
+        /// <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)
+        {
+            if (currencies == null) throw new ArgumentNullException(nameof(currencies));
+
+            var requestedCurrencies = ExtractRequestedCurrencies(currencies);
+
+            var rawData = FetchRatesFromEndpoints();
+            if (string.IsNullOrWhiteSpace(rawData))
+                return Enumerable.Empty<ExchangeRate>();
+
+            return ParseRates(rawData, requestedCurrencies);
+        }
+
+        private HashSet<string> ExtractRequestedCurrencies(IEnumerable<Currency> currencies)
+        {
+            return new HashSet<string>(
+                currencies.Select(c => c?.Code?.ToUpperInvariant())
+                          .Where(s => !string.IsNullOrEmpty(s))
+            );
+        }
+
+        private string FetchRatesFromEndpoints()
+        {
+            using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(HttpTimeoutSeconds) };
+            foreach (var url in _endpoints)
+            {
+                try
+                {
+                    var response = http.GetAsync(url).GetAwaiter().GetResult();
+                    if (response.IsSuccessStatusCode)
+                        return response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogWarning(ex, "Failed requesting CNB rate endpoint {Url}", url);
+                }
+            }
+            _logger.LogError("All CNB rate endpoints failed.");
+            return null;
+        }
+
+        private IEnumerable<ExchangeRate> ParseRates(string rawData, HashSet<string> requestedCurrencies)
+        {
+            var results = new List<ExchangeRate>();
+            var lines = rawData.Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries);
+
+            foreach (var line in lines)
+            {
+                var rate = ParseLine(line, requestedCurrencies);
+                if (rate != null)
+                    results.Add(rate);
+            }
+            return results;
+        }
+        private ExchangeRate ParseLine(string line, HashSet<string> requestedCurrencies)
+        {
+            try
+            {
+                if (!line.Contains("|"))
+                    return null;
+
+                var parts = line.Split('|');
+                if (parts.Length < 5)
+                    return null;
+
+                var code = parts[3].Trim().ToUpperInvariant();
+                if (!requestedCurrencies.Contains(code))
+                    return null;
+                var amountText = parts[2].Trim();
+                var rateText = parts[4].Trim().Replace(',', '.');
+
+                if (!decimal.TryParse(amountText, NumberStyles.Number, CultureInfo.InvariantCulture, out var amount))
+                    amount = 1m;
+
+                if (!decimal.TryParse(rateText, NumberStyles.Number, CultureInfo.InvariantCulture, out var rate))
+                    return null;
+
+                if (amount != 0m && amount != 1m)
+                    rate = rate / amount;
+
+                return new ExchangeRate(new Currency(code), new Currency(TargetCurrency), rate);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "CNB line parsing failed for line: {Line}", line);
+                return null;
+            }
+        }
+    }
+}