CSV_TO_PDF_REPORT/code/src/EnvelopeRenderer.Desktop.Tests/CsvPreviewLoaderTests.cs

using EnvelopeRenderer.Desktop.Core.Csv;

namespace EnvelopeRenderer.Desktop.Tests;

public sealed class CsvPreviewLoaderTests : IDisposable
{
    private readonly string _tempDirectory =
        Path.Combine(Path.GetTempPath(), "EnvelopeRenderer.Desktop.Tests", Guid.NewGuid().ToString("N"));

    public CsvPreviewLoaderTests()
    {
        Directory.CreateDirectory(_tempDirectory);
    }

    public void Dispose()
    {
        if (Directory.Exists(_tempDirectory))
        {
            Directory.Delete(_tempDirectory, recursive: true);
        }
    }

    private string WriteCsv(string contents)
    {
        var path = Path.Combine(_tempDirectory, $"{Guid.NewGuid():N}.csv");
        File.WriteAllText(path, contents);
        return path;
    }

    [Fact]
    public void TryLoad_ValidHeaderAndRows_ReturnsHeadersAndSampleRows()
    {
        var path = WriteCsv(
            "Full Name,Address1,City\r\n" +
            "Jane Doe,123 Main St,Springfield\r\n" +
            "John Smith,456 Oak Ave,Shelbyville\r\n");

        var loaded = CsvPreviewLoader.TryLoad(path, out var result, out var errors);

        Assert.True(loaded);
        Assert.Empty(errors);
        Assert.NotNull(result);
        Assert.Equal(new[] { "Full Name", "Address1", "City" }, result!.Headers);
        Assert.Equal(2, result.SampleRows.Count);
        Assert.Equal(new[] { "Jane Doe", "123 Main St", "Springfield" }, result.SampleRows[0]);
        Assert.Equal(new[] { "John Smith", "456 Oak Ave", "Shelbyville" }, result.SampleRows[1]);
    }

    [Fact]
    public void TryLoad_MoreRowsThanMaxSample_ReturnsOnlyTheBoundedSample()
    {
        var lines = new List<string> { "Col1,Col2" };
        for (var i = 0; i < 50; i++)
        {
            lines.Add($"value{i}a,value{i}b");
        }

        var path = WriteCsv(string.Join("\r\n", lines) + "\r\n");

        var loaded = CsvPreviewLoader.TryLoad(path, out var result, out var errors, maxSampleRows: 10);

        Assert.True(loaded);
        Assert.Empty(errors);
        Assert.Equal(10, result!.SampleRows.Count);
        Assert.Equal(new[] { "value0a", "value0b" }, result.SampleRows[0]);
        Assert.Equal(new[] { "value9a", "value9b" }, result.SampleRows[9]);
    }

    [Fact]
    public void TryLoad_EmptyFile_ReturnsClearError()
    {
        var path = WriteCsv(string.Empty);

        var loaded = CsvPreviewLoader.TryLoad(path, out var result, out var errors);

        Assert.False(loaded);
        Assert.Null(result);
        Assert.Contains(errors, e => e.Contains("empty", StringComparison.OrdinalIgnoreCase));
    }

    [Fact]
    public void TryLoad_MalformedCsv_ReturnsClearErrorInsteadOfThrowing()
    {
        // An unterminated quoted field is invalid CSV that CsvHelper detects and rejects rather
        // than silently misparsing.
        var path = WriteCsv("Full Name,Address1\r\n\"Jane Doe,123 Main St\r\n");

        var exception = Record.Exception(() => CsvPreviewLoader.TryLoad(path, out var result, out var errors));

        Assert.Null(exception);

        var loaded = CsvPreviewLoader.TryLoad(path, out var loadedResult, out var loadedErrors);
        Assert.False(loaded);
        Assert.Null(loadedResult);
        Assert.NotEmpty(loadedErrors);
    }

    [Fact]
    public void TryLoad_MissingFile_ReturnsClearError()
    {
        var path = Path.Combine(_tempDirectory, "does-not-exist.csv");

        var loaded = CsvPreviewLoader.TryLoad(path, out var result, out var errors);

        Assert.False(loaded);
        Assert.Null(result);
        Assert.Contains(errors, e => e.Contains("not found", StringComparison.OrdinalIgnoreCase));
    }

    [Fact]
    public void TryLoad_BlankPath_ReturnsClearError()
    {
        var loaded = CsvPreviewLoader.TryLoad(string.Empty, out var result, out var errors);

        Assert.False(loaded);
        Assert.Null(result);
        Assert.NotEmpty(errors);
    }

    [Fact]
    public void TryLoad_HeaderOnlyFile_ReturnsHeadersWithNoSampleRows()
    {
        var path = WriteCsv("Full Name,Address1\r\n");

        var loaded = CsvPreviewLoader.TryLoad(path, out var result, out var errors);

        Assert.True(loaded);
        Assert.Empty(errors);
        Assert.Equal(new[] { "Full Name", "Address1" }, result!.Headers);
        Assert.Empty(result.SampleRows);
    }
}