// (c) Copyright Ascensio System SIA 2010-2022
//
// This program is a free software product.
// You can redistribute it and/or modify it under the terms
// of the GNU Affero General Public License (AGPL) version 3 as published by the Free Software
// Foundation. In accordance with Section 7(a) of the GNU AGPL its Section 15 shall be amended
// to the effect that Ascensio System SIA expressly excludes the warranty of non-infringement of
// any third-party rights.
//
// This program is distributed WITHOUT ANY WARRANTY, without even the implied warranty
// of MERCHANTABILITY or FITNESS FOR A PARTICULAR  PURPOSE. For details, see
// the GNU AGPL at: http://www.gnu.org/licenses/agpl-3.0.html
//
// You can contact Ascensio System SIA at Lubanas st. 125a-25, Riga, Latvia, EU, LV-1021.
//
// The  interactive user interfaces in modified source and object code versions of the Program must
// display Appropriate Legal Notices, as required under Section 5 of the GNU AGPL version 3.
//
// Pursuant to Section 7(b) of the License you must retain the original Product logo when
// distributing the program. Pursuant to Section 7(e) we decline to grant you any rights under
// trademark law for use of our trademarks.
//
// All the Product's GUI elements, including illustrations and icon sets, as well as technical writing
// content are licensed under the terms of the Creative Commons Attribution-ShareAlike 4.0
// International. See the License terms at http://creativecommons.org/licenses/by-sa/4.0/legalcode

namespace ASC.Common.Utils;

public static class MimeHeaderUtils
{
    public static string EncodeMime(string mimeHeaderValue)
    {
        return EncodeMime(mimeHeaderValue, Encoding.UTF8, false);
    }

    public static string EncodeMime(string mimeHeaderValue, Encoding charset, bool split)
    {
        if (MustEncode(mimeHeaderValue))
        {
            var result = new StringBuilder();
            var data = charset.GetBytes(mimeHeaderValue);
            var maxEncodedTextSize = split ? 75 - ("=?" + charset.WebName + "?" + "B"/*Base64 encode*/ + "?" + "?=").Length : int.MaxValue;

            result.Append("=?" + charset.WebName + "?B?");
            var stored = 0;
            var base64 = Convert.ToBase64String(data);

            for (var i = 0; i < base64.Length; i += 4)
            {
                // Encoding buffer full, create new encoded-word.
                if (stored + 4 > maxEncodedTextSize)
                {
                    result.Append("?=\r\n =?" + charset.WebName + "?B?");
                    stored = 0;
                }

                result.Append(base64, i, 4);
                stored += 4;
            }

            result.Append("?=");

            return result.ToString();
        }

        return mimeHeaderValue;
    }

    public static bool MustEncode(string text)
    {
        return !string.IsNullOrEmpty(text) && text.Any(c => c > 127);
    }
}