Implement CNB exchange rate provider - Natalia Dorofeieva

jobs/Backend/Task/ExchangeRateUpdater.Api/Endpoints/ExchangeRateEndpoints.cs

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+using ExchangeRateUpdater.Application.Interfaces;
+using ExchangeRateUpdater.Application.Validation;
+
+namespace ExchangeRateUpdater.Api.Endpoints;
+
+public static class ExchangeRateEndpoints
+{
+    public static void MapExchangeRatesEndpoints(this WebApplication app)
+    {
+        app.MapGet("/exchange-rates", async (
+                string[] currencies, 
+                IExchangeRateProvider exchangeRateProvider,
+                CancellationToken cancellationToken) =>
+            {
+                var validator = new ExchangeRatesRequestValidator();
+                var validationResult = await validator.ValidateAsync(currencies, cancellationToken);
+                if (!validationResult.IsValid)
+                {
+                    return Results.BadRequest(validationResult.Errors.Select(e => e.ErrorMessage));
+                }
+
+                var result = await exchangeRateProvider.GetExchangeRates(currencies, cancellationToken);
+
+                return Results.Ok(result);
+            })
+            .WithName("GetExchangeRates")
+            .WithDescription("Gets exchange rates for provided currencies to CZK from Czech National Bank")
+            .WithTags("Exchange Rates");
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Api/ExchangeRateUpdater.Api.csproj

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+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="FluentValidation.DependencyInjectionExtensions" Version="12.1.1" />
+        <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.2"/>
+        <PackageReference Include="Swashbuckle.AspNetCore" Version="10.1.0" />
+    </ItemGroup>
+
+    <ItemGroup>
+      <ProjectReference Include="..\ExchangeRateUpdater.Application\ExchangeRateUpdater.Application.csproj" />
+      <ProjectReference Include="..\ExchangeRateUpdater.Infrastructure\ExchangeRateUpdater.Infrastructure.csproj" />
+    </ItemGroup>
+
+</Project>

jobs/Backend/Task/ExchangeRateUpdater.Api/ExchangeRateUpdater.Api.http

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+@HostAddress = https://localhost:7232
+
+### Get exchange rates for EUR and USD
+GET {{HostAddress}}/exchange-rates?currencies=eur&currencies=usd
+Accept: application/json

jobs/Backend/Task/ExchangeRateUpdater.Api/Program.cs

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+using ExchangeRateUpdater.Api.Endpoints;
+using ExchangeRateUpdater.Application.Configuration;
+using ExchangeRateUpdater.Application.Interfaces;
+using ExchangeRateUpdater.Application.Services;
+using ExchangeRateUpdater.Infrastructure.HttpClients;
+using Microsoft.Extensions.Options;
+
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddEndpointsApiExplorer();
+builder.Services.AddSwaggerGen();
+
+builder.Services.AddScoped<IExchangeRateProvider, ExchangeRateProvider>();
+
+builder.Services.Configure<ExchangeRateConfig>(
+    builder.Configuration.GetSection("ExchangeRateConfig"));
+
+builder.Services.AddSingleton<ExchangeRateConfig>(sp =>
+    sp.GetRequiredService<IOptions<ExchangeRateConfig>>().Value);
+
+builder.Services.AddHttpClient<IExchangeRateApiClient, ExchangeRateApiClient>((sp, client) =>
+{
+    var config = sp.GetRequiredService<IOptions<ExchangeRateConfig>>().Value;
+    client.BaseAddress = new Uri(config.BaseUrl);
+    client.Timeout = TimeSpan.FromSeconds(config.Timeout);
+});
+
+var app = builder.Build();
+
+if (app.Environment.IsDevelopment())
+{
+    app.UseSwagger();
+    app.UseSwaggerUI();
+}
+
+app.UseHttpsRedirection();
+
+app.MapExchangeRatesEndpoints();
+
+app.Run();

jobs/Backend/Task/ExchangeRateUpdater.Api/Properties/launchSettings.json

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+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "https": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "launchUrl": "swagger/index.html",
+      "applicationUrl": "https://localhost:7232;http://localhost:5028",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

jobs/Backend/Task/ExchangeRateUpdater.Api/appsettings.Development.json

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+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

jobs/Backend/Task/ExchangeRateUpdater.Api/appsettings.json

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+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*",
+  "ExchangeRateConfig": {
+    "DefaultCurrency": "CZK",
+    "BaseUrl": "https://api.cnb.cz/cnbapi/",
+    "Timeout": 30,
+    "RatePrecision": 3
+  }
+}

jobs/Backend/Task/ExchangeRateUpdater.Application/Configuration/ExchangeRateConfig.cs

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+namespace ExchangeRateUpdater.Application.Configuration;
+
+public sealed class ExchangeRateConfig
+{
+    public string BaseUrl { get; set; }
+
+    public string DefaultCurrency { get; set; }
+
+    public int Timeout { get; set; }
+
+    public int RatePrecision { get; set; }
+}

jobs/Backend/Task/ExchangeRateUpdater.Application/ExchangeRateUpdater.Application.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <Reference Include="Microsoft.Extensions.Logging.Abstractions">
+        <HintPath>..\..\..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.AspNetCore.App\10.0.2\Microsoft.Extensions.Logging.Abstractions.dll</HintPath>
+      </Reference>
+      <Reference Include="Microsoft.Extensions.Options">
+        <HintPath>..\..\..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.AspNetCore.App\10.0.2\Microsoft.Extensions.Options.dll</HintPath>
+      </Reference>
+    </ItemGroup>
+
+    <ItemGroup>
+      <PackageReference Include="FluentValidation" Version="12.1.1" />
+    </ItemGroup>
+
+</Project>

jobs/Backend/Task/ExchangeRateUpdater.Application/Interfaces/IExchangeRateApiClient.cs

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+using ExchangeRateUpdater.Application.Models;
+
+namespace ExchangeRateUpdater.Application.Interfaces;
+
+public interface IExchangeRateApiClient
+{
+    Task<IEnumerable<CnbExchangeRate>> GetAllExchangeRatesAsync(CancellationToken cancellationToken);
+}

jobs/Backend/Task/ExchangeRateUpdater.Application/Interfaces/IExchangeRateProvider.cs

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+using ExchangeRateUpdater.Application.Models;
+
+namespace ExchangeRateUpdater.Application.Interfaces;
+
+public interface IExchangeRateProvider
+{
+    Task<List<ExchangeRate>> GetExchangeRates(string[] currencies, CancellationToken cancellationToken);
+}

jobs/Backend/Task/ExchangeRateUpdater.Application/Models/CnbExchangeRate.cs

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+namespace ExchangeRateUpdater.Application.Models;
+
+public sealed record CnbExchangeRate(string CurrencyCode, decimal Rate, int Amount);

jobs/Backend/Task/ExchangeRateUpdater.Application/Models/CnbExchangeRateResponse.cs

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+namespace ExchangeRateUpdater.Application.Models;
+
+public sealed record CnbExchangeRateResponse(CnbExchangeRate[] Rates);

jobs/Backend/Task/ExchangeRateUpdater.Application/Models/ExchangeRate.cs

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+namespace ExchangeRateUpdater.Application.Models;
+
+public sealed record ExchangeRate(string SourceCurrency, string TargetCurrency, decimal Rate);

jobs/Backend/Task/ExchangeRateUpdater.Application/Services/ExchangeRateProvider.cs

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+using ExchangeRateUpdater.Application.Configuration;
+using ExchangeRateUpdater.Application.Interfaces;
+using ExchangeRateUpdater.Application.Models;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace ExchangeRateUpdater.Application.Services;
+
+public sealed class ExchangeRateProvider : IExchangeRateProvider
+{
+    private readonly IExchangeRateApiClient _apiClient;
+    private readonly ExchangeRateConfig _exchangeRateConfig;
+    private readonly ILogger<ExchangeRateProvider> _logger;
+
+    public ExchangeRateProvider(
+        IExchangeRateApiClient apiClient, 
+        IOptions<ExchangeRateConfig> exchangeRateConfig,
+        ILogger<ExchangeRateProvider> logger)
+    {
+        _apiClient = apiClient;
+        _exchangeRateConfig = exchangeRateConfig.Value;
+        _logger = logger;
+    }
+
+    public async Task<List<ExchangeRate>> GetExchangeRates(string[] currencies, CancellationToken cancellationToken)
+    {
+        var cnbExchangeRates = await _apiClient.GetAllExchangeRatesAsync(cancellationToken);
+        return MapExchangeRates(cnbExchangeRates, currencies).ToList();
+    }
+
+    private IEnumerable<ExchangeRate> MapExchangeRates(
+        IEnumerable<CnbExchangeRate> cnbExchangeRates,
+        string[] currencyCodes)
+    {
+        var rateByCurrencyCode =
+            cnbExchangeRates.ToDictionary(x => x.CurrencyCode, StringComparer.OrdinalIgnoreCase);
+        foreach (var currencyCode in currencyCodes)
+        {
+            if (!rateByCurrencyCode.TryGetValue(currencyCode, out var exchangeRate))
+            {
+                _logger.LogWarning("No matches were found among CNB rates for currency '{@currencyCode}'", currencyCode);
+                continue;
+            }
+
+            yield return new(
+                exchangeRate.CurrencyCode,
+                _exchangeRateConfig.DefaultCurrency,
+                Math.Round(exchangeRate.Rate / exchangeRate.Amount, _exchangeRateConfig.RatePrecision));
+        }
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Application/Validation/ExchangeRatesRequestValidator.cs

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+using FluentValidation;
+
+namespace ExchangeRateUpdater.Application.Validation;
+
+public sealed class ExchangeRatesRequestValidator : AbstractValidator<string[]>
+{
+    public ExchangeRatesRequestValidator()
+    {
+        RuleFor(x => x)
+            .NotEmpty()
+            .WithMessage("No currencies were provided as input");
+
+        RuleForEach(x => x)
+            .NotEmpty()
+            .WithMessage("Currency must not be empty")
+            .Matches("^[A-Za-z]{3}$")
+            .WithMessage("Each currency must be a 3-letter code. Example: USD");
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater.Infrastructure/ExchangeRateUpdater.Infrastructure.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <ProjectReference Include="..\ExchangeRateUpdater.Application\ExchangeRateUpdater.Application.csproj" />
+    </ItemGroup>
+
+    <ItemGroup>
+      <Reference Include="Microsoft.Extensions.DependencyInjection.Abstractions">
+        <HintPath>..\..\..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.AspNetCore.App\10.0.2\Microsoft.Extensions.DependencyInjection.Abstractions.dll</HintPath>
+      </Reference>
+      <Reference Include="Microsoft.Extensions.Logging.Abstractions">
+        <HintPath>..\..\..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.AspNetCore.App\10.0.2\Microsoft.Extensions.Logging.Abstractions.dll</HintPath>
+      </Reference>
+      <Reference Include="Microsoft.Extensions.Options">
+        <HintPath>..\..\..\..\..\..\..\..\Program Files\dotnet\shared\Microsoft.AspNetCore.App\10.0.2\Microsoft.Extensions.Options.dll</HintPath>
+      </Reference>
+    </ItemGroup>
+
+</Project>