#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;
using log4net.Core;

namespace log4net.Appender
{
  /// <summary>
  /// This appender forwards logging events to attached appenders.
  /// </summary>
  /// <remarks>
  /// <para>
  /// The forwarding appender can be used to specify different thresholds
  /// and filters for the same appender at different locations within the hierarchy.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  public class ForwardingAppender : AppenderSkeleton, IAppenderAttachable
  {
    /// <summary>
    /// Closes the appender and releases resources.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Releases any resources allocated within the appender such as file handles, 
    /// network connections, etc.
    /// </para>
    /// <para>
    /// It is a programming error to append to a closed appender.
    /// </para>
    /// </remarks>
    protected override void OnClose()
    {
      // Remove all the attached appenders
      lock (this)
      {
        m_appenderAttachedImpl?.RemoveAllAppenders();
      }
    }

    /// <summary>
    /// Forward the logging event to the attached appenders 
    /// </summary>
    /// <param name="loggingEvent">The event to log.</param>
    /// <remarks>
    /// <para>
    /// Delivers the logging event to all the attached appenders.
    /// </para>
    /// </remarks>
    protected override void Append(LoggingEvent loggingEvent)
    {
      // Pass the logging event on to the attached appenders
      m_appenderAttachedImpl?.AppendLoopOnAppenders(loggingEvent);
    }

    /// <summary>
    /// Forward the logging events to the attached appenders 
    /// </summary>
    /// <param name="loggingEvents">The array of events to log.</param>
    /// <remarks>
    /// <para>
    /// Delivers the logging events to all the attached appenders.
    /// </para>
    /// </remarks>
    protected override void Append(LoggingEvent[] loggingEvents)
    {
      // Pass the logging event on to the attached appenders
      m_appenderAttachedImpl?.AppendLoopOnAppenders(loggingEvents);
    }

    /// <summary>
    /// Adds an <see cref="IAppender" /> to the list of appenders of this
    /// instance.
    /// </summary>
    /// <param name="newAppender">The <see cref="IAppender" /> to add to this appender.</param>
    /// <remarks>
    /// <para>
    /// If the specified <see cref="IAppender" /> is already in the list of
    /// appenders, then it won't be added again.
    /// </para>
    /// </remarks>
    public virtual void AddAppender(IAppender newAppender)
    {
      if (newAppender is null)
      {
        throw new ArgumentNullException(nameof(newAppender));
      }
      lock (this)
      {
        m_appenderAttachedImpl ??= new AppenderAttachedImpl();
        m_appenderAttachedImpl.AddAppender(newAppender);
      }
    }

    /// <summary>
    /// Gets the appenders contained in this appender as an 
    /// <see cref="System.Collections.ICollection"/>.
    /// </summary>
    /// <remarks>
    /// If no appenders can be found, then an <see cref="EmptyCollection"/> 
    /// is returned.
    /// </remarks>
    /// <returns>
    /// A collection of the appenders in this appender.
    /// </returns>
    public virtual AppenderCollection Appenders
    {
      get
      {
        lock (this)
        {
          return m_appenderAttachedImpl?.Appenders ?? AppenderCollection.EmptyCollection;
        }
      }
    }

    /// <summary>
    /// Looks for the appender with the specified name.
    /// </summary>
    /// <param name="name">The name of the appender to lookup.</param>
    /// <returns>
    /// The appender with the specified name, or <c>null</c>.
    /// </returns>
    /// <remarks>
    /// <para>
    /// Get the named appender attached to this appender.
    /// </para>
    /// </remarks>
    public virtual IAppender? GetAppender(string? name)
    {
      lock (this)
      {
        if (m_appenderAttachedImpl is null || name is null)
        {
          return null;
        }

        return m_appenderAttachedImpl.GetAppender(name);
      }
    }

    /// <summary>
    /// Removes all previously added appenders from this appender.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This is useful when re-reading configuration information.
    /// </para>
    /// </remarks>
    public virtual void RemoveAllAppenders()
    {
      lock (this)
      {
        if (m_appenderAttachedImpl is not null)
        {
          m_appenderAttachedImpl.RemoveAllAppenders();
          m_appenderAttachedImpl = null;
        }
      }
    }

    /// <summary>
    /// Removes the specified appender from the list of appenders.
    /// </summary>
    /// <param name="appender">The appender to remove.</param>
    /// <returns>The appender removed from the list</returns>
    /// <remarks>
    /// The appender removed is not closed.
    /// If you are discarding the appender you must call
    /// <see cref="IAppender.Close"/> on the appender removed.
    /// </remarks>
    public virtual IAppender? RemoveAppender(IAppender? appender)
    {
      lock (this)
      {
        if (appender is not null && m_appenderAttachedImpl is not null)
        {
          return m_appenderAttachedImpl.RemoveAppender(appender);
        }
      }
      return null;
    }

    /// <summary>
    /// Removes the appender with the specified name from the list of appenders.
    /// </summary>
    /// <param name="name">The name of the appender to remove.</param>
    /// <returns>The appender removed from the list</returns>
    /// <remarks>
    /// The appender removed is not closed.
    /// If you are discarding the appender you must call
    /// <see cref="IAppender.Close"/> on the appender removed.
    /// </remarks>
    public virtual IAppender? RemoveAppender(string? name)
    {
      lock (this)
      {
        if (name is not null && m_appenderAttachedImpl is not null)
        {
          return m_appenderAttachedImpl.RemoveAppender(name);
        }
      }
      return null;
    }

    /// <summary>
    /// Implementation of the <see cref="IAppenderAttachable"/> interface
    /// </summary>
    private AppenderAttachedImpl? m_appenderAttachedImpl;
  }
}
