#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.Util;

namespace log4net.Core
{
  /// <summary>
  /// The <see cref="SecurityContextProvider"/> providers default <see cref="SecurityContext"/> instances.
  /// </summary>
  /// <remarks>
  /// <para>
  /// A configured component that interacts with potentially protected system
  /// resources uses a <see cref="SecurityContext"/> to provide the elevated
  /// privileges required. If the <see cref="SecurityContext"/> object has
  /// been not been explicitly provided to the component then the component
  /// will request one from this <see cref="SecurityContextProvider"/>.
  /// </para>
  /// <para>
  /// By default the <see cref="SecurityContextProvider.DefaultProvider"/> is
  /// an instance of <see cref="SecurityContextProvider"/> which returns only
  /// <see cref="NullSecurityContext"/> objects. This is a reasonable default
  /// where the privileges required are not know by the system.
  /// </para>
  /// <para>
  /// This default behavior can be overridden by subclassing the <see cref="SecurityContextProvider"/>
  /// and overriding the <see cref="CreateSecurityContext"/> method to return
  /// the desired <see cref="SecurityContext"/> objects. The default provider
  /// can be replaced by programmatically setting the value of the 
  /// <see cref="SecurityContextProvider.DefaultProvider"/> property.
  /// </para>
  /// <para>
  /// An alternative is to use the <c>log4net.Config.SecurityContextProviderAttribute</c>
  /// This attribute can be applied to an assembly in the same way as the
  /// <c>log4net.Config.XmlConfiguratorAttribute"</c>. The attribute takes
  /// the type to use as the <see cref="SecurityContextProvider"/> as an argument.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  public class SecurityContextProvider
  {
    /// <summary>
    /// The default provider
    /// </summary>
    private static SecurityContextProvider s_defaultProvider = new SecurityContextProvider();

    /// <summary>
    /// Gets or sets the default SecurityContextProvider
    /// </summary>
    /// <value>
    /// The default SecurityContextProvider
    /// </value>
    /// <remarks>
    /// <para>
    /// The default provider is used by configured components that
    /// require a <see cref="SecurityContext"/> and have not had one
    /// given to them.
    /// </para>
    /// <para>
    /// By default this is an instance of <see cref="SecurityContextProvider"/>
    /// that returns <see cref="NullSecurityContext"/> objects.
    /// </para>
    /// <para>
    /// The default provider can be set programmatically by setting
    /// the value of this property to a sub class of <see cref="SecurityContextProvider"/>
    /// that has the desired behavior.
    /// </para>
    /// </remarks>
    public static SecurityContextProvider DefaultProvider
    {
      get { return s_defaultProvider; }
      set { s_defaultProvider = value; }
    }

    /// <summary>
    /// Protected default constructor to allow subclassing
    /// </summary>
    /// <remarks>
    /// <para>
    /// Protected default constructor to allow subclassing
    /// </para>
    /// </remarks>
    protected SecurityContextProvider()
    {
    }

    /// <summary>
    /// Create a SecurityContext for a consumer
    /// </summary>
    /// <param name="consumer">The consumer requesting the SecurityContext</param>
    /// <returns>An impersonation context</returns>
    /// <remarks>
    /// <para>
    /// The default implementation is to return a <see cref="NullSecurityContext"/>.
    /// </para>
    /// <para>
    /// Subclasses should override this method to provide their own
    /// behavior.
    /// </para>
    /// </remarks>
    public virtual SecurityContext CreateSecurityContext(object consumer)
    {
      return NullSecurityContext.Instance;
    }
  }
}
