Copy the statistics table and graph to the clipboard

Copy All takes whichever tab is open, as N1MM's does: the table off the table
tab, a picture of the graph off the graph tab. Copy Table as Text and Copy
Graph as Image do either one from either tab.

`StatisticsTable` lays the pivot out as the window prints it — the headings,
the rows, the Total line — and pads it into columns for the text form, so the
grid, the clipboard and Print to File all say the same thing.

X11 asks for a picture when the other program pastes rather than when it is
copied, so the bitmap given to the clipboard is held until the clipboard is
given a different one. Disposing it at the end of the copy killed the program
on the next paste; the table pasted into a second Avalonia program reads back
lined up, and the picture reads back as a 916x438 bitmap.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PdAYHcdRktqKry7nk414TU

src/Nonemm.Session/StatisticsTable.cs

@@ -0,0 +1,119 @@
+using System.Text;
+
+namespace Nonemm.Session;
+
+/// The pivot laid out the way the statistics window prints it: N1MM's headings,
+/// one line per row with the label columns first and the `Tot` and `Accum`
+/// columns last, and the `Total` line at the bottom.
+public sealed class StatisticsTable
+{
+    /// What goes between two columns in the text form.
+    private const string Between = "  ";
+
+    private StatisticsTable(
+        IReadOnlyList<string> headings,
+        IReadOnlyList<IReadOnlyList<string>> rows,
+        int labelColumns)
+    {
+        Headings = headings;
+        Rows = rows;
+        LabelColumns = labelColumns;
+    }
+
+    public static StatisticsTable Of(StatisticsPivot pivot)
+    {
+        List<string> headings =
+        [
+            .. pivot.Row.Headings,
+            .. pivot.Columns.Select(Heading),
+            "Tot",
+            "Accum",
+        ];
+        int labels = pivot.Row.Headings.Count;
+        List<IReadOnlyList<string>> rows = [];
+        for (int down = 0; down < pivot.Rows.Count; down++)
+        {
+            List<string> cells = [pivot.Rows[down].First];
+            if (labels == 2)
+            {
+                cells.Add(pivot.Rows[down].Second);
+            }
+            for (int across = 0; across < pivot.Columns.Count; across++)
+            {
+                cells.Add(Count(pivot.Count(down, across)));
+            }
+            cells.Add(Count(pivot.RowTotals[down]));
+            cells.Add(Count(pivot.Accumulated[down]));
+            rows.Add(cells);
+        }
+
+        List<string> total = ["Total"];
+        if (labels == 2)
+        {
+            total.Add("");
+        }
+        total.AddRange(pivot.ColumnTotals.Select(Count));
+        total.Add(Count(pivot.Total));
+        total.Add(Count(pivot.Total));
+        rows.Add(total);
+        return new StatisticsTable(headings, rows, labels);
+    }
+
+    public IReadOnlyList<string> Headings { get; }
+
+    /// Every line, the `Total` line last.
+    public IReadOnlyList<IReadOnlyList<string>> Rows { get; }
+
+    /// How many columns at the left hold the row's own value rather than a
+    /// count. Two for Hour and Mode &amp; Band, one for every other field.
+    public int LabelColumns { get; }
+
+    /// The table with spaces between the columns, so it lines up under a
+    /// monospace font. The label columns are left-aligned and the counts are
+    /// right-aligned, as they are on the screen.
+    public string ToText()
+    {
+        int[] widths = new int[Headings.Count];
+        for (int at = 0; at < Headings.Count; at++)
+        {
+            widths[at] = Math.Max(Headings[at].Length, Rows.Max(r => At(r, at).Length));
+        }
+        StringBuilder text = new();
+        Line(text, Headings, widths);
+        foreach (IReadOnlyList<string> row in Rows)
+        {
+            Line(text, row, widths);
+        }
+        return text.ToString();
+    }
+
+    private void Line(StringBuilder text, IReadOnlyList<string> cells, int[] widths)
+    {
+        for (int at = 0; at < widths.Length; at++)
+        {
+            string cell = At(cells, at);
+            text.Append(at < LabelColumns ? cell.PadRight(widths[at]) : cell.PadLeft(widths[at]));
+            if (at < widths.Length - 1)
+            {
+                text.Append(Between);
+            }
+        }
+        // a row of blanks at the right would otherwise leave the line ragged
+        while (text.Length > 0 && text[^1] == ' ')
+        {
+            text.Length--;
+        }
+        text.Append('\n');
+    }
+
+    private static string At(IReadOnlyList<string> cells, int at) => at < cells.Count ? cells[at] : "";
+
+    /// A column with no value of its own is headed the way the window heads it,
+    /// so the text and the screen say the same thing.
+    private static string Heading(PivotKey column) =>
+        column.Label.Length > 0 ? column.Label : "(none)";
+
+    /// N1MM leaves a cell with nothing in it blank rather than printing a zero,
+    /// so the shape of the operating shows through the table.
+    private static string Count(int count) => count == 0 ? "" : count.ToString();
+}