using System.IO;
using System.Text;

namespace SharepointToolbox.Services.Export;

/// <summary>
/// Central file-write plumbing for export services so every CSV and HTML
/// artefact gets a consistent encoding: CSV files are written with a UTF-8
/// BOM (required for Excel to detect the encoding when opening a
/// double-clicked .csv), HTML files are written without a BOM (some browsers
/// and iframe <c>srcdoc</c> paths render the BOM as a visible character).
/// Export services should call these helpers rather than constructing
/// <see cref="UTF8Encoding"/> inline.
/// </summary>
internal static class ExportFileWriter
{
    private static readonly UTF8Encoding Utf8WithBom = new(encoderShouldEmitUTF8Identifier: true);
    private static readonly UTF8Encoding Utf8NoBom   = new(encoderShouldEmitUTF8Identifier: false);

    /// <summary>Writes <paramref name="csv"/> to <paramref name="filePath"/> as UTF-8 with BOM.</summary>
    public static Task WriteCsvAsync(string filePath, string csv, CancellationToken ct)
        => File.WriteAllTextAsync(filePath, csv, Utf8WithBom, ct);

    /// <summary>Writes <paramref name="html"/> to <paramref name="filePath"/> as UTF-8 without BOM.</summary>
    public static Task WriteHtmlAsync(string filePath, string html, CancellationToken ct)
        => File.WriteAllTextAsync(filePath, html, Utf8NoBom, ct);
}