Feat: implement ExchangeRateProvider for Czech National Bank

jobs/Backend/Task.Tests/Domain/CnbDailyTxtParserTests.cs

@@ -0,0 +1,169 @@
+using ExchangeRateUpdater.Domain;
+using Xunit;
+
+namespace Task.Tests.Domain;
+
+public sealed class CnbDailyTxtParserTests
+{
+    [Fact]
+    public void Parse_valid_payload_returns_correct_rates()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Australia|dollar|1|AUD|14,123
+            United States|dollar|1|usd|22,640
+            """;
+
+        ExchangeRate[] rates = CnbDailyTxtParser.Parse(payload).ToArray();
+
+        Assert.Equal(2, rates.Length);
+        Assert.Equal("AUD", rates[0].SourceCurrency.Code);
+        Assert.Equal("CZK", rates[0].TargetCurrency.Code);
+        Assert.Equal(14.123m, rates[0].Value);
+        Assert.Equal("USD", rates[1].SourceCurrency.Code);
+        Assert.Equal(22.640m, rates[1].Value);
+    }
+
+    [Fact]
+    public void Parse_amount_greater_than_one_normalizes_value()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Japan|yen|100|JPY|15,320
+            """;
+
+        ExchangeRate rate = CnbDailyTxtParser.Parse(payload).Single();
+
+        Assert.Equal("JPY", rate.SourceCurrency.Code);
+        Assert.Equal(0.1532m, rate.Value);
+    }
+
+    [Fact]
+    public void Parse_skips_header_lines_correctly()
+    {
+        string payload = """
+            22.04.2026 #78
+            This line is metadata
+            Another metadata line
+            Country|Currency|Amount|Code|Rate
+            Sweden|krona|1|sek|2,078
+            """;
+
+        ExchangeRate rate = CnbDailyTxtParser.Parse(payload).Single();
+
+        Assert.Equal("SEK", rate.SourceCurrency.Code);
+        Assert.Equal("CZK", rate.TargetCurrency.Code);
+        Assert.Equal(2.078m, rate.Value);
+    }
+
+    [Fact]
+    public void Parse_accepts_dot_decimal_from_english_cnb_endpoint()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Australia|dollar|1|AUD|14.795
+            Japan|yen|100|JPY|15.320
+            """;
+
+        ExchangeRate[] rates = CnbDailyTxtParser.Parse(payload).ToArray();
+
+        Assert.Equal(2, rates.Length);
+        Assert.Equal("AUD", rates[0].SourceCurrency.Code);
+        Assert.Equal(14.795m, rates[0].Value);
+        Assert.Equal("JPY", rates[1].SourceCurrency.Code);
+        Assert.Equal(0.1532m, rates[1].Value);
+    }
+
+    [Fact]
+    public void Parse_malformed_line_throws_with_line_number()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Australia|dollar|1|AUD
+            """;
+
+        FormatException ex = Assert.Throws<FormatException>(() => CnbDailyTxtParser.Parse(payload).ToArray());
+
+        Assert.Contains("Malformed CNB line.", ex.Message);
+        Assert.Contains("Line 3", ex.Message);
+    }
+
+    [Fact]
+    public void Parse_invalid_decimal_throws()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Australia|dollar|oops|AUD|14,123
+            """;
+
+        FormatException ex = Assert.Throws<FormatException>(() => CnbDailyTxtParser.Parse(payload).ToArray());
+
+        Assert.Contains("Invalid amount in CNB line.", ex.Message);
+        Assert.Contains("Line 3", ex.Message);
+    }
+
+    [Fact]
+    public void Parse_missing_header_throws()
+    {
+        string payload = """
+            22.04.2026 #78
+            Metadata line
+            Australia|dollar|1|AUD|14,123
+            """;
+
+        FormatException ex = Assert.Throws<FormatException>(() => CnbDailyTxtParser.Parse(payload).ToArray());
+
+        Assert.Contains("Missing CNB header line.", ex.Message);
+    }
+
+    [Fact]
+    public void Parse_rejects_zero_or_negative_amount()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Australia|dollar|0|AUD|14,123
+            """;
+
+        FormatException ex = Assert.Throws<FormatException>(() => CnbDailyTxtParser.Parse(payload).ToArray());
+
+        Assert.Contains("Amount must be greater than zero.", ex.Message);
+        Assert.Contains("Line 3", ex.Message);
+    }
+
+    [Fact]
+    public void Parse_rejects_zero_or_negative_rate()
+    {
+        string payload = """
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            Australia|dollar|1|AUD|0
+            """;
+
+        FormatException ex = Assert.Throws<FormatException>(() => CnbDailyTxtParser.Parse(payload).ToArray());
+
+        Assert.Contains("Rate must be greater than zero.", ex.Message);
+        Assert.Contains("Line 3", ex.Message);
+    }
+
+    [Fact]
+    public void Parse_malformed_line_longer_than_100_chars_is_truncated_in_error()
+    {
+        string longCountryName = new('A', 101);
+        string payload = $"""
+            22.04.2026 #78
+            Country|Currency|Amount|Code|Rate
+            {longCountryName}|dollar|1|AUD
+            """;
+
+        FormatException ex = Assert.Throws<FormatException>(() => CnbDailyTxtParser.Parse(payload).ToArray());
+
+        Assert.Contains("...", ex.Message);
+        Assert.DoesNotContain(longCountryName, ex.Message);
+    }
+}

jobs/Backend/Task.Tests/Domain/DomainInvariantsTests.cs

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+using ExchangeRateUpdater.Domain;
+using Xunit;
+
+namespace Task.Tests.Domain;
+
+public sealed class DomainInvariantsTests
+{
+    [Fact]
+    public void Currency_normalizes_code()
+    {
+        Currency currency = new(" usd ");
+
+        Assert.Equal("USD", currency.Code);
+    }
+
+    [Fact]
+    public void Currency_empty_or_whitespace_throws()
+    {
+        Assert.Throws<ArgumentException>(() => new Currency(""));
+        Assert.Throws<ArgumentException>(() => new Currency("   "));
+    }
+
+    [Fact]
+    public void ExchangeRate_requires_non_null_currencies()
+    {
+        Currency czk = new("CZK");
+
+        Assert.Throws<ArgumentNullException>(() => new ExchangeRate(null!, czk, 1m));
+        Assert.Throws<ArgumentNullException>(() => new ExchangeRate(new Currency("USD"), null!, 1m));
+    }
+
+    [Fact]
+    public void ExchangeRate_requires_positive_value()
+    {
+        Currency usd = new("USD");
+        Currency czk = new("CZK");
+
+        Assert.Throws<ArgumentOutOfRangeException>(() => new ExchangeRate(usd, czk, 0m));
+        Assert.Throws<ArgumentOutOfRangeException>(() => new ExchangeRate(usd, czk, -1m));
+    }
+}

jobs/Backend/Task.Tests/Infrastructure/CnbOptionsValidatorTests.cs

@@ -0,0 +1,87 @@
+using ExchangeRateUpdater.Infrastructure;
+using Xunit;
+
+namespace Task.Tests.Infrastructure;
+
+public sealed class CnbOptionsValidatorTests
+{
+    private readonly CnbOptionsValidator _validator = new();
+
+    [Fact]
+    public void Validate_valid_http_url_returns_success()
+    {
+        CnbOptions options = new()
+        {
+            Url = "http://www.cnb.cz/cs/financni-trhy/devizovy-trh/kurzy-devizoveho-trhu/denni_kurz.txt"
+        };
+
+        var result = _validator.Validate(name: null, options);
+
+        Assert.True(result.Succeeded);
+    }
+
+    [Fact]
+    public void Validate_valid_https_url_returns_success()
+    {
+        CnbOptions options = new()
+        {
+            Url = "https://www.cnb.cz/cs/financni-trhy/devizovy-trh/kurzy-devizoveho-trhu/denni_kurz.txt"
+        };
+
+        var result = _validator.Validate(name: null, options);
+
+        Assert.True(result.Succeeded);
+    }
+
+    [Fact]
+    public void Validate_relative_url_returns_failure()
+    {
+        CnbOptions options = new()
+        {
+            Url = "/cs/financni-trhy/devizovy-trh/kurzy-devizoveho-trhu/denni_kurz.txt"
+        };
+
+        var result = _validator.Validate(name: null, options);
+
+        Assert.False(result.Succeeded);
+    }
+
+    [Fact]
+    public void Validate_non_http_scheme_returns_failure()
+    {
+        CnbOptions options = new()
+        {
+            Url = "ftp://www.cnb.cz/path"
+        };
+
+        var result = _validator.Validate(name: null, options);
+
+        Assert.False(result.Succeeded);
+    }
+
+    [Fact]
+    public void Validate_empty_url_returns_failure()
+    {
+        CnbOptions options = new()
+        {
+            Url = ""
+        };
+
+        var result = _validator.Validate(name: null, options);
+
+        Assert.False(result.Succeeded);
+    }
+
+    [Fact]
+    public void Validate_malformed_url_returns_failure()
+    {
+        CnbOptions options = new()
+        {
+            Url = "http://"
+        };
+
+        var result = _validator.Validate(name: null, options);
+
+        Assert.False(result.Succeeded);
+    }
+}