// Hook: AfterCalculation
// Stamp every visible worksheet with a small watermark in cell A1.
//
// The watermark shows the report output name and generation timestamp so
// recipients always see provenance even if the workbook is saved and reopened
// later. Hidden sheets are skipped.

using System.Drawing;

foreach (var ws in Workbook.Worksheets)
{
    if (!ws.IsVisible) continue;

    ws.Cells["A1"].PutValue($"{OutputName} - Generated {DateTime.Now:yyyy-MM-dd HH:mm}");

    var style = ws.Cells["A1"].GetStyle();
    style.Font.IsBold = false;
    style.Font.IsItalic = true;
    style.Font.Color = Color.Gray;
    ws.Cells["A1"].SetStyle(style);
}

var visibleCount = Workbook.Worksheets.Count(w => w.IsVisible);
Logger.LogInformation($"Watermark stamped on {visibleCount} visible sheet(s).");