Dev
65 lines
3.1 KiB
C#
65 lines
3.1 KiB
C#
using System.IO;
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using System.Text;
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namespace SharepointToolbox.Services.Export;
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/// <summary>
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/// Central file-write plumbing for export services so every CSV and HTML
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/// artefact gets a consistent encoding: CSV files are written with a UTF-8
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/// BOM (required for Excel to detect the encoding when opening a
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/// double-clicked .csv), HTML files are written without a BOM (some browsers
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/// and iframe <c>srcdoc</c> paths render the BOM as a visible character).
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/// Export services should call these helpers rather than constructing
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/// <see cref="UTF8Encoding"/> inline.
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/// </summary>
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internal static class ExportFileWriter
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{
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private static readonly UTF8Encoding Utf8WithBom = new(encoderShouldEmitUTF8Identifier: true);
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private static readonly UTF8Encoding Utf8NoBom = new(encoderShouldEmitUTF8Identifier: false);
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/// <summary>Writes <paramref name="csv"/> to <paramref name="filePath"/> as UTF-8 with BOM.</summary>
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public static Task WriteCsvAsync(string filePath, string csv, CancellationToken ct)
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=> File.WriteAllTextAsync(filePath, csv, Utf8WithBom, ct);
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/// <summary>Writes <paramref name="html"/> to <paramref name="filePath"/> as UTF-8 without BOM.</summary>
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public static Task WriteHtmlAsync(string filePath, string html, CancellationToken ct)
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=> File.WriteAllTextAsync(filePath, html, Utf8NoBom, ct);
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/// <summary>
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/// Streams a <see cref="StringBuilder"/> directly to disk as UTF-8 with
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/// BOM, chunk by chunk. Avoids the full-document <c>ToString()</c> copy
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/// and the separate UTF-8 byte buffer that <see cref="File.WriteAllTextAsync(string, string, Encoding, CancellationToken)"/>
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/// would otherwise allocate — meaningful for large CSV exports.
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/// </summary>
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public static Task WriteCsvChunksAsync(string filePath, StringBuilder builder, CancellationToken ct)
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=> WriteChunksAsync(filePath, builder, Utf8WithBom, ct);
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/// <summary>
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/// Streams a <see cref="StringBuilder"/> directly to disk as UTF-8 without
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/// BOM. Same rationale as <see cref="WriteCsvChunksAsync"/> — for large
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/// HTML reports it halves peak memory by skipping the intermediate string.
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/// </summary>
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public static Task WriteHtmlChunksAsync(string filePath, StringBuilder builder, CancellationToken ct)
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=> WriteChunksAsync(filePath, builder, Utf8NoBom, ct);
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private static async Task WriteChunksAsync(string filePath, StringBuilder builder, Encoding encoding, CancellationToken ct)
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{
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// FileOptions.Asynchronous lets StreamWriter use true async I/O.
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await using var fs = new FileStream(
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filePath,
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FileMode.Create,
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FileAccess.Write,
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FileShare.None,
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bufferSize: 64 * 1024,
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options: FileOptions.Asynchronous | FileOptions.SequentialScan);
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await using var sw = new StreamWriter(fs, encoding, bufferSize: 64 * 1024);
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foreach (var chunk in builder.GetChunks())
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{
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ct.ThrowIfCancellationRequested();
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await sw.WriteAsync(chunk, ct);
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}
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await sw.FlushAsync(ct);
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}
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}
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