ExchangeRateProvider Implementation for Daily Exchange Rates Loading

jobs/Backend/Task/ExchangeRateUpdater.sln

@@ -3,18 +3,44 @@ 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}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ExchangeRateUpdater", "ExchangeRateUpdater\ExchangeRateUpdater.csproj", "{7B2695D6-D24C-4460-A58E-A10F08550CE0}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ExchangeRateUpdaterTests", "ExchangeRateUpdaterTests\ExchangeRateUpdaterTests.csproj", "{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
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 		Release|Any CPU = Release|Any CPU
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+		Release|x86 = Release|x86
 	EndGlobalSection
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+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Debug|Any CPU.Build.0 = Debug|Any CPU
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+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Debug|x64.Build.0 = Debug|Any CPU
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+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Debug|x86.Build.0 = Debug|Any CPU
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+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Release|Any CPU.Build.0 = Release|Any CPU
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+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Release|x64.Build.0 = Release|Any CPU
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+		{AADC1E9A-EE54-4BB2-B24D-8E048DD38F9A}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

jobs/Backend/Task/ExchangeRateUpdater/Contracts/IDateTimeService.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace ExchangeRateUpdater.Contracts;
+
+public interface IDateTimeService
+{
+    DateTime GetUtcNow();
+
+    DateTime GetNow();
+
+    DateTime GetToday();
+}

jobs/Backend/Task/ExchangeRateUpdater/Contracts/IExchangeRateLoader.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using ExchangeRateUpdater.Models;
+
+namespace ExchangeRateUpdater.Contracts;
+
+public interface IExchangeRateLoader
+{
+    IRateRefreshScheduler RateRefreshSchedule { get; }
+    Task<IEnumerable<ExchangeRate>> GetExchangeRatesAsync(IEnumerable<string> currencies, DateTime date);
+}

jobs/Backend/Task/ExchangeRateUpdater/Contracts/IRateRefreshSchedule.cs

@@ -0,0 +1,8 @@
+using System;
+
+namespace ExchangeRateUpdater.Contracts;
+
+public interface IRateRefreshScheduler
+{
+    DateTimeOffset GetNextRefreshTime();
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/Cnb/CnbExchangeRateLoader.cs

@@ -0,0 +1,94 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Globalization;
+using System.Linq;
+using System.Net.Http;
+using System.Text.Json;
+using System.Threading.Tasks;
+using ExchangeRateUpdater.Contracts;
+using ExchangeRateUpdater.DataSource.Cnb.Dto;
+using ExchangeRateUpdater.DataSources;
+using ExchangeRateUpdater.Infrastructure;
+using ExchangeRateUpdater.Infrastructure.Config;
+using ExchangeRateUpdater.Models;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+
+namespace ExchangeRateUpdater.DataSource.Cnb;
+
+internal class CnbExchangeRateLoader : IExchangeRateLoader
+{
+    private const string DailyExchangeRateUrlPath = "/cnbapi/exrates/daily?date={0}&lang=EN";
+    private readonly IRequestHandler requestHandler;
+    private readonly CnbRateConverter converter;
+    private readonly ILogger<CnbExchangeRateLoader> logger;
+    private readonly IDateTimeService dateTimeService;
+    private readonly Uri baseApiUri;
+    private readonly JsonSerializerOptions serializerOptions = new JsonSerializerOptions(JsonSerializerDefaults.Web);
+
+    public CnbExchangeRateLoader(IRequestHandler requestHandler,
+    CnbRateConverter converter,
+    ILogger<CnbExchangeRateLoader> logger,
+    IRefreshScheduleFactory refreshScheduleFactory,
+    IDateTimeService dateTimeService,
+    [FromKeyedServices(Constants.CnbServiceKey)] ExchangeRateLoaderConfig config)
+    {
+        this.requestHandler = requestHandler;
+        this.converter = converter;
+        this.logger = logger;
+        this.dateTimeService = dateTimeService;
+        baseApiUri = new Uri(config.BaseApiUrl);
+        RateRefreshSchedule = refreshScheduleFactory.CreateRefreshSchedule(config.RefreshScheduleConfig);
+        logger.LogInformation("Initialized data source with URL {} and refresh schedule: {}", baseApiUri, RateRefreshSchedule);
+    }
+
+    public IRateRefreshScheduler RateRefreshSchedule { get; }
+
+    // discussable: can consider adding "retry" logic inside this method. In this case the method will need CancellationToken parameter to stop pending retries.
+    public async Task<IEnumerable<ExchangeRate>> GetExchangeRatesAsync(IEnumerable<string> currencies, DateTime date)
+    {
+        ArgumentNullException.ThrowIfNull(currencies);
+
+        if (date >= dateTimeService.GetToday().AddDays(1))
+            throw new ArgumentException("The date should not be in the future", nameof(date));
+
+        if (!currencies.Any())
+        {
+            return [];
+        }
+
+        try
+        {
+            var dateParam = date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture);
+            var requestUri = new Uri(baseApiUri, string.Format(DailyExchangeRateUrlPath, dateParam)).ToString();
+
+            var stopwatch = new Stopwatch();
+            stopwatch.Start();
+
+            using var stream = await requestHandler.GetStreamAsync(requestUri);
+
+            CnbRateResponse response = await JsonSerializer.DeserializeAsync<CnbRateResponse>(stream, serializerOptions);
+
+            stopwatch.Stop(); // Further the elapsed time can be put into metrics
+            logger.LogInformation("Loaded {} rates in {} ms", response.Rates.Length, stopwatch.ElapsedMilliseconds);
+
+            var requestedCurrencies = new HashSet<string>(currencies);
+            var result = response.Rates
+                .Where(r => requestedCurrencies.Contains(r.CurrencyCode))
+                .Select(converter.Convert)
+                .Where(r => r != null)
+                .ToList();
+
+            return result;
+        }
+        catch (HttpRequestException ex)
+        {
+            throw new RateLoaderException($"API responded with error status code: {ex.StatusCode}", ex);
+        }
+        catch (Exception ex)
+        {
+            throw new RateLoaderException("Unable load exchange rates from CNB", ex);
+        }
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/Cnb/CnbRateConverter.cs

@@ -0,0 +1,29 @@
+using System;
+using ExchangeRateUpdater.DataSource.Cnb.Dto;
+using ExchangeRateUpdater.Models;
+using Microsoft.Extensions.Logging;
+
+namespace ExchangeRateUpdater.DataSource.Cnb;
+
+internal class CnbRateConverter
+{
+    private readonly ILogger<CnbRateConverter> logger;
+
+    public CnbRateConverter( ILogger<CnbRateConverter> logger)
+    {
+        this.logger = logger;
+    }
+
+    public ExchangeRate Convert(CnbRate rate)
+    {
+        IsoCurrencyCode sourceCurrency;
+        // poor man validation
+        if (!Enum.TryParse(rate.CurrencyCode, out sourceCurrency) || rate.Amount <= 0)
+        {
+            logger.LogWarning("Invalid rate for {} received from CNB, ignoring", rate.CurrencyCode);
+            return null;
+        }
+
+        return new ExchangeRate(new Currency(sourceCurrency), new Currency(IsoCurrencyCode.CZK), rate.Rate / rate.Amount);
+    }
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/Cnb/Dto/CnbRate.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Text.Json.Serialization;
+
+namespace ExchangeRateUpdater.DataSource.Cnb.Dto;
+
+internal sealed record CnbRate
+{
+    [JsonPropertyName("amount")]
+    public long Amount { get; init; }
+
+    [JsonPropertyName("country")]
+    public string Country { get; init; }
+
+    [JsonPropertyName("currency")]
+    public string Currency { get; init; }
+
+    [JsonPropertyName("currencyCode")]
+    public string CurrencyCode { get; init; }
+
+    [JsonPropertyName("order")]
+    public int Order { get; init; }
+
+    [JsonPropertyName("rate")]
+    public Decimal Rate { get; init; }
+
+    [JsonPropertyName("validFor")]
+    public string ValidFor { get; init; }
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/Cnb/Dto/CnbRateResponse.cs

@@ -0,0 +1,9 @@
+using System.Text.Json.Serialization;
+
+namespace ExchangeRateUpdater.DataSource.Cnb.Dto;
+
+internal sealed record CnbRateResponse
+{
+    [JsonPropertyName("rates")]
+    public CnbRate[] Rates { get; init; }
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/RateLoaderException.cs

@@ -0,0 +1,7 @@
+using System;
+
+namespace ExchangeRateUpdater.DataSources;
+
+public class RateLoaderException(string message, Exception inner) : Exception(message, inner)
+{
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/RefreshSchedule/DefaultRateRefreshScheduler.cs

@@ -0,0 +1,32 @@
+using System;
+using ExchangeRateUpdater.Contracts;
+
+namespace ExchangeRateUpdater.DataSources.RefreshSchedule;
+
+internal class DefaultRateRefreshScheduler : IRateRefreshScheduler
+{
+    private readonly TimeOnly time;
+    private readonly TimeZoneInfo timeZone;
+    private readonly IDateTimeService dateTimeService;
+
+    public DefaultRateRefreshScheduler(TimeOnly time, TimeZoneInfo timeZone, IDateTimeService dateTimeService)
+    {
+        this.time = time;
+        this.timeZone = timeZone;
+        this.dateTimeService = dateTimeService;
+    }
+
+    public DateTimeOffset GetNextRefreshTime()
+    {
+        var refreshTimeForCurrentDateInUtc =
+            TimeZoneInfo.ConvertTimeToUtc(new DateTime(DateOnly.FromDateTime(dateTimeService.GetToday()), time, DateTimeKind.Unspecified), timeZone);
+
+        DateTime nextRefreshDate = dateTimeService.GetUtcNow() < refreshTimeForCurrentDateInUtc ?
+            refreshTimeForCurrentDateInUtc :
+            refreshTimeForCurrentDateInUtc.AddDays(1);
+
+        return nextRefreshDate;
+    }
+
+    public override string ToString() => $"{time:t} {timeZone.StandardName}";
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/RefreshSchedule/NoRefreshScheduler.cs

@@ -0,0 +1,11 @@
+using System;
+using ExchangeRateUpdater.Contracts;
+
+namespace ExchangeRateUpdater.DataSources.RefreshSchedule;
+
+internal sealed class NoRefreshScheduler : IRateRefreshScheduler
+{
+    public DateTimeOffset GetNextRefreshTime() => DateTimeOffset.MaxValue;
+
+    public override string ToString() => "No refresh";
+}

jobs/Backend/Task/ExchangeRateUpdater/DataSources/RefreshSchedule/RefreshScheduleFactory.cs

@@ -0,0 +1,27 @@
+using System;
+using ExchangeRateUpdater.Contracts;
+using ExchangeRateUpdater.Infrastructure;
+using ExchangeRateUpdater.Infrastructure.Config;
+
+namespace ExchangeRateUpdater.DataSources.RefreshSchedule;
+
+internal class RefreshScheduleFactory : IRefreshScheduleFactory
+{
+    private readonly IDateTimeService dateTimeService;
+
+    public RefreshScheduleFactory(IDateTimeService dateTimeService)
+    {
+        this.dateTimeService = dateTimeService;
+    }
+
+    public IRateRefreshScheduler CreateRefreshSchedule(RefreshScheduleConfig config)
+    {
+        return config == null
+                ? new NoRefreshScheduler()
+                : new DefaultRateRefreshScheduler(
+                            TimeOnly.Parse(config.Time),
+                            TimeZoneInfo.FindSystemTimeZoneById(config.TimeZone),
+                            dateTimeService);
+
+    }
+}