Implement CNB exchange rate provider

.gitignore

@@ -21,3 +21,6 @@
 node_modules
 bower_components
 npm-debug.log
+
+.vs/
+CopilotIndices*/

jobs/Backend/ExchangeRateUpdater.Tests/CnbExchangeRateProviderTests/MapToExchangeRatesTests.cs

@@ -0,0 +1,123 @@
+using ExchangeRateUpdater.Providers;
+using FluentAssertions;
+using System.Reflection;
+
+namespace ExchangeRateUpdater.Tests.CnbExchangeRateProviderTests
+{
+    public class MapToExchangeRatesTests
+    {
+        private readonly object _provider;
+        private readonly MethodInfo _parseMethod;
+        private readonly MethodInfo _mapMethod;
+
+        public MapToExchangeRatesTests()
+        {
+            var type = typeof(CnbExchangeRateProvider);
+            _provider = Activator.CreateInstance(type)!;
+
+            _parseMethod = type.GetMethod("ParseDailyRates", BindingFlags.NonPublic | BindingFlags.Instance)!;
+            _mapMethod = type.GetMethod("MapToExchangeRates", BindingFlags.NonPublic | BindingFlags.Instance)!;
+        }
+
+        private object InvokeParse(string raw)
+        {
+            try
+            {
+                return _parseMethod.Invoke(_provider, new object[] { raw })!;
+            }
+            catch (TargetInvocationException ex)
+            {
+                throw ex.InnerException ?? ex;
+            }
+        }
+
+        private object InvokeMap(object rows, params Currency[] currencies)
+        {
+            try
+            {
+                return _mapMethod.Invoke(_provider, new object[] { rows, currencies })!;
+            }
+            catch (TargetInvocationException ex)
+            {
+                throw ex.InnerException ?? ex;
+            }
+        }
+
+        [Fact]
+        public void Map_ValidRow_ReturnsNormalizedRate()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        Japan|yen|100|JPY|15.0";
+
+            var rows = InvokeParse(txt);
+
+            var result = (System.Collections.Generic.IEnumerable<ExchangeRate>)InvokeMap(rows,
+                new Currency("JPY"));
+
+            var rate = result.Single();
+
+            rate.Value.Should().Be(0.15m);
+        }
+
+        [Fact]
+        public void Map_RequestMissingCurrency_ReturnsEmpty()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        USA|dollar|1|USD|20.0";
+
+            var rows = InvokeParse(txt);
+
+            var result = (IEnumerable<ExchangeRate>)InvokeMap(rows,
+                new Currency("EUR"));
+
+            result.Should().BeEmpty();
+        }
+
+        [Fact]
+        public void Map_MultipleRequestedSameCode_NoDuplicateRatesReturned()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        USA|dollar|1|USD|20.0";
+
+            var rows = InvokeParse(txt);
+
+            var result = (IEnumerable<ExchangeRate>)InvokeMap(rows,
+                new Currency("USD"), new Currency("USD"));
+
+            result.Should().HaveCount(1);
+        }
+
+        [Fact]
+        public void Map_RequestedCurrenciesIsEmpty_ReturnsEmpty()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        USA|dollar|1|USD|20.0";
+
+            var rows = InvokeParse(txt);
+
+            var result = (IEnumerable<ExchangeRate>)InvokeMap(rows);
+
+            result.Should().BeEmpty();
+        }
+
+        [Fact]
+        public void Map_DuplicateCurrencyCodesInRows_Throws()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        USA|dollar|1|USD|20.0
+                        United States|dollar|1|USD|21.0";
+
+            var rows = InvokeParse(txt);
+
+            Action act = () => InvokeMap(rows, new Currency("USD"));
+
+            act.Should().Throw<FormatException>()
+                .WithMessage("*duplicate*");
+        }
+    }
+}

jobs/Backend/ExchangeRateUpdater.Tests/CnbExchangeRateProviderTests/ParseDailyRatesTests.cs

@@ -0,0 +1,95 @@
+using ExchangeRateUpdater.Providers;
+using FluentAssertions;
+using System.Reflection;
+
+
+namespace ExchangeRateUpdater.Tests.CnbExchangeRateProviderTests
+{
+    public class ParseDailyRatesTests
+    {
+        private readonly object _provider;
+        private readonly MethodInfo _parseMethod;
+
+        public ParseDailyRatesTests()
+        {
+            var type = typeof(CnbExchangeRateProvider);
+            _provider = Activator.CreateInstance(type)!;
+
+            _parseMethod = type.GetMethod("ParseDailyRates", BindingFlags.NonPublic | BindingFlags.Instance)!;
+        }
+
+        private object InvokeParse(string raw)
+        {
+            try
+            {
+                return _parseMethod.Invoke(_provider, new object[] { raw })!;
+            }
+            catch (TargetInvocationException ex)
+            {
+                throw ex.InnerException ?? ex;
+            }
+        }
+
+        [Fact]
+        public void Parse_ValidContent_ReturnsRows()
+        {
+            // Arrange
+            var txt = @"03 Jan 2025 #1
+                        Country|Currency|Amount|Code|Rate
+                        USA|dollar|1|USD|20.796";
+
+            // Act
+            var result = InvokeParse(txt);
+
+            // Assert
+            var rows = (System.Collections.Generic.IReadOnlyList<object>)result;
+            rows.Should().HaveCount(1);
+        }
+
+        [Fact]
+        public void Parse_InvalidColumnCount_Throws()
+        {
+            var txt = @"03 Jan 2025 #1
+                        H1|H2|H3
+                        Bad|Row|Only3Cols";
+
+            Action act = () => InvokeParse(txt);
+
+            act.Should().Throw<FormatException>();
+        }
+
+        [Fact]
+        public void Parse_InvalidAmount_Throws()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        USA|dollar|XYZ|USD|20.5";
+
+            Action act = () => InvokeParse(txt);
+
+            act.Should().Throw<FormatException>()
+                .WithMessage("*amount*");
+        }
+
+        [Fact]
+        public void Parse_InvalidRate_Throws()
+        {
+            var txt = @"03 Jan 2025 #1
+                        C|C|C|C|C
+                        USA|dollar|1|USD|BAD";
+
+            Action act = () => InvokeParse(txt);
+
+            act.Should().Throw<FormatException>()
+                .WithMessage("*rate*");
+        }
+
+        [Fact]
+        public void Parse_EmptyContent_Throws()
+        {
+            Action act = () => InvokeParse("");
+
+            act.Should().Throw<FormatException>();
+        }
+    }
+}

jobs/Backend/ExchangeRateUpdater.Tests/ExchangeRateUpdater.Tests.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="FluentAssertions" Version="8.8.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector" Version="3.1.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Task\ExchangeRateUpdater.csproj" />
+  </ItemGroup>
+
+</Project>

jobs/Backend/ExchangeRateUpdater.Tests/Usings.cs

@@ -0,0 +1 @@
+global using Xunit;

jobs/Backend/Readme_Solution.md

@@ -0,0 +1,45 @@
+# Solution Overview
+
+This project implements an exchange rate provider for the Czech National Bank (CNB).
+The provider downloads the daily `daily.txt` file from the official CNB endpoint, parses it, and maps the data to the domain `ExchangeRate` model.
+
+## How it works
+
+1. The provider downloads the TXT file using `HttpClient` (async internally).
+2. The file is parsed into an internal `CnbRateRow` model (`Amount`, `Code`, `Rate`).
+3. Only currencies requested by the caller and available in the CNB data source are returned.
+4. CNB publishes rates in the format "foreign currency - CZK". The provider converts the CNB rate to “per one unit” using: value = Rate / Amount  
+5. The provider does not create synthetic or reverse exchange rates.
+
+## Design Notes
+
+- The public API remains synchronous to match the original task skeleton. Internal download logic uses async for correctness.
+- The `CnbRateRow` model is kept private because it represents a CNB-specific TXT structure and is not part of the domain model.
+- Duplicate currency codes in the CNB data are validated to ensure data quality.
+- The target currency is always CZK.
+- Minimal debug logging is implemented directly inside the provider. This keeps the code simple for a small console application.
+  In a real production service, structured logging (ILogger) would be used.
+
+## Running
+
+dotnet build
+dotnet run
+
+
+
+## Unit Tests
+
+A few unit tests were added to check the key logic of the CNB provider:
+
+- parsing the `daily.txt` file  
+- handling invalid or unexpected input  
+- mapping CNB rows to `ExchangeRate`  
+- preventing duplicate currency codes  
+
+Only the internal parsing/mapping is tested — the HTTP download is intentionally not covered to keep things simple.
+
+Tests use **xUnit** + **FluentAssertions**.
+
+### Running the tests
+
+dotnet test

jobs/Backend/Task/ExchangeRate.cs

@@ -1,4 +1,6 @@
-namespace ExchangeRateUpdater
+using System.Globalization;
+
+namespace ExchangeRateUpdater
 {
     public class ExchangeRate
     {
@@ -17,7 +19,7 @@ public ExchangeRate(Currency sourceCurrency, Currency targetCurrency, decimal va
 
         public override string ToString()
         {
-            return $"{SourceCurrency}/{TargetCurrency}={Value}";
+            return $"{SourceCurrency}/{TargetCurrency}={Value.ToString(CultureInfo.InvariantCulture)}";
         }
     }
 }

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 18
+VisualStudioVersion = 18.3.11218.70 d18.3
 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", "..\ExchangeRateUpdater.Tests\ExchangeRateUpdater.Tests.csproj", "{A5AB45FE-FA68-4A98-86F4-DF890B2D589D}"
+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
+		{A5AB45FE-FA68-4A98-86F4-DF890B2D589D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A5AB45FE-FA68-4A98-86F4-DF890B2D589D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A5AB45FE-FA68-4A98-86F4-DF890B2D589D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A5AB45FE-FA68-4A98-86F4-DF890B2D589D}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {F4DA4DC8-CEF4-4CDD-B5B5-736DBEAF50D5}
+	EndGlobalSection
 EndGlobal