Initial commit

Services/Export/BulkResultCsvExportService.cs

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+using System.Globalization;
+using System.IO;
+using System.Text;
+using CsvHelper;
+using CsvHelper.Configuration;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports the failed subset of a <see cref="BulkOperationSummary{T}"/> run
+/// to CSV. CsvHelper is used so the <typeparamref name="T"/> payload's
+/// properties become columns automatically, plus one error-message and one
+/// timestamp column appended at the end.
+/// </summary>
+public class BulkResultCsvExportService
+{
+    private static readonly CsvConfiguration CsvConfig = new(CultureInfo.InvariantCulture)
+    {
+        // Prevent CSV formula injection: prefix =, +, -, @, tab, CR with single quote
+        InjectionOptions = InjectionOptions.Escape,
+    };
+
+    /// <summary>
+    /// Builds a CSV containing only items whose <see cref="BulkItemResult{T}.IsSuccess"/>
+    /// is <c>false</c>. Columns: every public property of <typeparamref name="T"/>
+    /// followed by Error and Timestamp (ISO-8601).
+    /// </summary>
+    public string BuildFailedItemsCsv<T>(IReadOnlyList<BulkItemResult<T>> failedItems)
+    {
+        var TL = TranslationSource.Instance;
+        using var writer = new StringWriter();
+        using var csv = new CsvWriter(writer, CsvConfig);
+
+        csv.WriteHeader<T>();
+        csv.WriteField(TL["report.col.error"]);
+        csv.WriteField(TL["report.col.timestamp"]);
+        csv.NextRecord();
+
+        foreach (var item in failedItems.Where(r => !r.IsSuccess))
+        {
+            csv.WriteRecord(item.Item);
+            csv.WriteField(item.ErrorMessage);
+            csv.WriteField(item.Timestamp.ToString("o"));
+            csv.NextRecord();
+        }
+
+        return writer.ToString();
+    }
+
+    /// <summary>Writes the failed-items CSV to <paramref name="filePath"/> with UTF-8 BOM.</summary>
+    public async Task WriteFailedItemsCsvAsync<T>(
+        IReadOnlyList<BulkItemResult<T>> failedItems,
+        string filePath,
+        CancellationToken ct)
+    {
+        var content = BuildFailedItemsCsv(failedItems);
+        await ExportFileWriter.WriteCsvAsync(filePath, content, ct);
+    }
+}