/*
 * SonarLint for Visual Studio
 * Copyright (C) 2016-2017 SonarSource SA
 * mailto:info AT sonarsource DOT com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

using System;
using System.Runtime.InteropServices;
using System.Security;

namespace SonarLint.VisualStudio.Integration.Persistence
{
    internal static class SecureStringHelpers
    {
        // Copied from http://blogs.msdn.com/b/fpintos/archive/2009/06/12/how-to-properly-convert-securestring-to-string.aspx

        /// <summary>
        /// Create a read-only <see cref="SecureString"/> from this <see cref="string"/>.
        /// </summary>
        /// <returns>Read-only <see cref="SecureString"/></returns>
        public static SecureString ToSecureString(this string str)
        {
            if (str == null)
            {
                throw new ArgumentNullException(nameof(str));
            }

            var secure = new SecureString();
            foreach (char c in str)
            {
                secure.AppendChar(c);
            }
            secure.MakeReadOnly();
            return secure;
        }

        /// <summary>
        /// WARNING: This will create plain text <see cref="string"/> version of the <see cref="SecureString"/> in
        /// memory which is not encrypted. This could lead to leaking of sensitive information and other security
        /// vulnerabilities - heavy caution is advised.
        /// </summary>
        [SecurityCritical]
        public static string ToUnsecureString(this SecureString secureString)
        {
            if (secureString == null)
            {
                throw new ArgumentNullException(nameof(secureString));
            }

            IntPtr unmanagedString = IntPtr.Zero;
            try
            {
                unmanagedString = Marshal.SecureStringToGlobalAllocUnicode(secureString);
                return Marshal.PtrToStringUni(unmanagedString);
            }
            finally
            {
                Marshal.ZeroFreeGlobalAllocUnicode(unmanagedString);
            }
        }
    }
}