namespace MeetingAssistant.MeetingNotes;

internal readonly record struct MarkdownDocument(
    bool HasFrontmatter,
    string Frontmatter,
    string Body);

internal static class MarkdownDocumentParser
{
    public static MarkdownDocument SplitOptional(string content)
    {
        using var reader = new StringReader(content);
        if (reader.ReadLine() != "---")
        {
            return new MarkdownDocument(false, "", content);
        }

        var yaml = new List<string>();
        string? line;
        while ((line = reader.ReadLine()) is not null)
        {
            if (line == "---")
            {
                return new MarkdownDocument(
                    true,
                    string.Join(Environment.NewLine, yaml),
                    RemoveBodySeparator(reader.ReadToEnd()));
            }

            yaml.Add(line);
        }

        return new MarkdownDocument(false, "", content);
    }

    public static MarkdownDocument SplitRequired(
        string content,
        string missingFrontmatterMessage,
        string unclosedFrontmatterMessage)
    {
        using var reader = new StringReader(content);
        if (reader.ReadLine() != "---")
        {
            throw new InvalidDataException(missingFrontmatterMessage);
        }

        var yaml = new List<string>();
        string? line;
        while ((line = reader.ReadLine()) is not null)
        {
            if (line == "---")
            {
                return new MarkdownDocument(
                    true,
                    string.Join(Environment.NewLine, yaml),
                    RemoveBodySeparator(reader.ReadToEnd()));
            }

            yaml.Add(line);
        }

        throw new InvalidDataException(unclosedFrontmatterMessage);
    }

    private static string RemoveBodySeparator(string body)
    {
        if (body.StartsWith("\r\n", StringComparison.Ordinal))
        {
            return body[2..];
        }

        return body.StartsWith('\n')
            ? body[1..]
            : body;
    }
}