#region Apache License
//
// Licensed to the Apache Software Foundation (ASF) under one or more 
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership. 
// The ASF licenses this file to you under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with 
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;

using log4net.Core;

namespace log4net.Util;

/// <summary>
/// A SecurityContext used when a SecurityContext is not required
/// </summary>
/// <remarks>
/// <para>
/// The <see cref="NullSecurityContext"/> is a no-op implementation of the
/// <see cref="SecurityContext"/> base class. It is used where a <see cref="SecurityContext"/>
/// is required but one has not been provided.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
public sealed class NullSecurityContext : SecurityContext
{
  /// <summary>
  /// Singleton instance of <see cref="NullSecurityContext"/>
  /// </summary>
  /// <remarks>
  /// <para>
  /// Singleton instance of <see cref="NullSecurityContext"/>
  /// </para>
  /// </remarks>
  public static readonly NullSecurityContext Instance = new();

  /// <summary>
  /// Private constructor
  /// </summary>
  /// <remarks>
  /// <para>
  /// Private constructor for singleton pattern.
  /// </para>
  /// </remarks>
  private NullSecurityContext()
  {
  }

  /// <summary>
  /// Impersonate this SecurityContext
  /// </summary>
  /// <param name="state">State supplied by the caller</param>
  /// <returns><see langword="null"/></returns>
  /// <remarks>
  /// <para>
  /// No impersonation is done and <see langword="null"/> is always returned.
  /// </para>
  /// </remarks>
  public override IDisposable? Impersonate(object state) => null;
}
