chapter-organizer/Core/Printing/MarkdownTableStencil.cs

namespace Core.Printing;

/// <summary>
/// Splits a markdown template that contains exactly one table so a roster can
/// share one header and append merged body rows per record.
/// </summary>
public sealed class MarkdownTableStencil
{
    public required string Prefix { get; init; }

    public required string Header { get; init; }

    public required string Body { get; init; }

    public required string Suffix { get; init; }

    public static bool TryParse(string? template, out MarkdownTableStencil? stencil)
    {
        stencil = null;
        if (string.IsNullOrWhiteSpace(template))
            return false;

        var lines = SplitLines(template);
        if (!TryFindTable(lines, 0, out var headerIndex, out var bodyStart, out var bodyEnd))
            return false;

        if (bodyStart >= bodyEnd)
            return false;

        if (TryFindTable(lines, bodyEnd, out _, out _, out _))
            return false;

        stencil = new MarkdownTableStencil
        {
            Prefix = JoinLines(lines[..headerIndex]),
            Header = JoinLines(lines[headerIndex..bodyStart]),
            Body = JoinLines(lines[bodyStart..bodyEnd]),
            Suffix = JoinLines(lines[bodyEnd..])
        };
        return true;
    }

    public string Stitch(string prefix, IEnumerable<string> bodies, string suffix)
    {
        ArgumentNullException.ThrowIfNull(bodies);

        List<string> parts = [];
        AppendPart(parts, prefix);
        AppendPart(parts, Header);
        foreach (var body in bodies)
            AppendPart(parts, body);
        AppendPart(parts, suffix);

        return parts.Count == 0 ? string.Empty : string.Join('\n', parts) + "\n";
    }

    private static void AppendPart(List<string> parts, string? part)
    {
        if (string.IsNullOrEmpty(part))
            return;

        var trimmed = part.TrimEnd('\r', '\n');
        if (trimmed.Length > 0)
            parts.Add(trimmed);
    }

    private static bool TryFindTable(
        string[] lines,
        int start,
        out int headerIndex,
        out int bodyStart,
        out int bodyEnd)
    {
        headerIndex = -1;
        bodyStart = -1;
        bodyEnd = -1;

        for (var i = start; i < lines.Length - 1; i++)
        {
            if (!IsTableLine(lines[i]) || !IsSeparatorLine(lines[i + 1]))
                continue;

            headerIndex = i;
            bodyStart = i + 2;
            bodyEnd = bodyStart;
            while (bodyEnd < lines.Length && IsTableLine(lines[bodyEnd]) && !IsSeparatorLine(lines[bodyEnd]))
                bodyEnd++;
            return true;
        }

        return false;
    }

    private static bool IsTableLine(string line)
    {
        var trimmed = line.TrimStart();
        return trimmed.StartsWith('|');
    }

    private static bool IsSeparatorLine(string line) =>
        IsTableLine(line) && line.Contains("---", StringComparison.Ordinal);

    private static string[] SplitLines(string text) =>
        text.Replace("\r\n", "\n", StringComparison.Ordinal).Replace('\r', '\n').Split('\n');

    private static string JoinLines(string[] lines) =>
        lines.Length == 0 ? string.Empty : string.Join('\n', lines);
}