namespace LehrerApp.Templating;

public static class TemplateMetadataKeys
{
    public const string Language = "language";
    public const string ReportType = "report-type";
}

public static class TemplateMetadataText
{
    public const string FileName = "metadata.txt";

    public static Dictionary<string, string> Parse(string source)
    {
        var result = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        var lines = source.Replace("\r\n", "\n", StringComparison.Ordinal).Replace('\r', '\n').Split('\n');
        for (var index = 0; index < lines.Length; index++)
        {
            var line = lines[index].Trim();
            if (line.Length == 0 || line.StartsWith('#')) continue;
            var separator = line.IndexOf('=');
            if (separator < 1)
                throw new InvalidDataException($"Metadatenzeile {index + 1} muss Schlüssel=Wert enthalten.");
            var key = line[..separator].Trim();
            var value = line[(separator + 1)..].Trim();
            Validate(key, value);
            if (!result.TryAdd(key, value))
                throw new InvalidDataException($"Metadatenschlüssel „{key}“ ist mehrfach vorhanden.");
        }
        return result;
    }

    public static string Serialize(IReadOnlyDictionary<string, string> metadata)
    {
        if (metadata.Count == 0) return "";
        var lines = new List<string>(metadata.Count);
        foreach (var (key, value) in metadata.OrderBy(x => x.Key, StringComparer.OrdinalIgnoreCase))
        {
            Validate(key, value);
            lines.Add($"{key.Trim()}={value.Trim()}");
        }
        return string.Join('\n', lines) + "\n";
    }

    private static void Validate(string key, string value)
    {
        if (string.IsNullOrWhiteSpace(key)) throw new InvalidDataException("Ein Metadatenschlüssel darf nicht leer sein.");
        if (key.Contains('=') || key.Contains('\n') || key.Contains('\r'))
            throw new InvalidDataException($"Metadatenschlüssel „{key}“ enthält ein unzulässiges Zeichen.");
        if (value.Contains('\n') || value.Contains('\r'))
            throw new InvalidDataException($"Metadatenwert für „{key}“ darf nur eine Zeile umfassen.");
    }
}