// Copyright (c) 2020, Oracle and/or its affiliates.
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License, version 2.0, as
// published by the Free Software Foundation.
//
// This program is also distributed with certain software (including
// but not limited to OpenSSL) that is licensed under separate terms,
// as designated in a particular file or component or in included license
// documentation.  The authors of MySQL hereby grant you an
// additional permission to link the program and your derivative works
// with the separately licensed software that they have included with
// MySQL.
//
// Without limiting anything contained in the foregoing, this file,
// which is part of MySQL Connector/NET, is also subject to the
// Universal FOSS Exception, version 1.0, a copy of which can be found at
// http://oss.oracle.com/licenses/universal-foss-exception.
//
// 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 General Public License, version 2.0, for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software Foundation, Inc.,
// 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA

using System;
using System.Runtime.InteropServices;

namespace MySql.Data.Authentication.GSSAPI.Utility
{
    /// <summary>
    /// Memory pinned object
    /// </summary>
    internal static class Pinned
    {
        /// <summary>
        /// Create memory pinned object from <paramref name="value"/>
        /// </summary>
        /// <typeparam name="T">Any class type</typeparam>
        /// <param name="value">Value to pin</param>
        /// <returns>Pinned value</returns>
        internal static Pinned<T> From<T>(T value) where T : class => new Pinned<T>(value);
    }

    /// <summary>
    /// Memory pinned object
    /// </summary>
    /// <typeparam name="T">Any class type</typeparam>
    internal sealed class Pinned<T> : IDisposable where T : class
    {
        /// <summary>
        /// Original object value, can be used with <code>ref</code>
        /// </summary>
        internal readonly T Value;

        /// <summary>
        /// In memory address of the object
        /// </summary>
        internal IntPtr Address { get; }

        private GCHandle _handle;

        /// <summary>
        /// Create memory pinned object from <paramref name="value"/>
        /// </summary>
        /// <param name="value">Value to pin</param>
        internal Pinned(T value)
        {
            this.Value = value;
            this._handle = GCHandle.Alloc(value, GCHandleType.Pinned);
            this.Address = this._handle.AddrOfPinnedObject();
        }

        /// <summary>
        /// Returns address of object in memory
        /// </summary>
        public static implicit operator IntPtr(Pinned<T> p)
        {
            return p.Address;
        }

        /// <summary>
        /// Returns original object value
        /// </summary>
        public static implicit operator T(Pinned<T> p)
        {
            return p.Value;
        }

        public void Dispose()
        {
            this._handle.Free();
        }
    }
}