#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.Repository.Hierarchy
{
  /// <summary>
  /// The <see cref="RootLogger" /> sits at the root of the logger hierarchy tree. 
  /// </summary>
  /// <remarks>
  /// <para>
  /// The <see cref="RootLogger" /> is a regular <see cref="Logger" /> except 
  /// that it provides several guarantees.
  /// </para>
  /// <para>
  /// First, it cannot be assigned a <c>null</c>
  /// level. Second, since the root logger cannot have a parent, the
  /// <see cref="EffectiveLevel"/> property always returns the value of the
  /// level field without walking the hierarchy.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  public class RootLogger : Logger
  {
    /// <summary>
    /// Construct a <see cref="RootLogger"/>
    /// </summary>
    /// <param name="level">The level to assign to the root logger.</param>
    /// <remarks>
    /// <para>
    /// Initializes a new instance of the <see cref="RootLogger" /> class with
    /// the specified logging level.
    /// </para>
    /// <para>
    /// The root logger names itself as "root". However, the root
    /// logger cannot be retrieved by name.
    /// </para>
    /// </remarks>
    public RootLogger(Level level) : base("root")
    {
      Level = level;
    }

    /// <summary>
    /// Gets the assigned level value without walking the logger hierarchy.
    /// </summary>
    /// <value>The assigned level value without walking the logger hierarchy.</value>
    /// <remarks>
    /// <para>
    /// Because the root logger cannot have a parent and its level
    /// must not be <c>null</c> this property just returns the
    /// value of <see cref="Logger.Level"/>.
    /// </para>
    /// </remarks>
    public override Level EffectiveLevel => base.Level!;

    /// <summary>
    /// Gets or sets the assigned <see cref="Level"/> for the root logger.  
    /// </summary>
    /// <value>
    /// The <see cref="Level"/> of the root logger.
    /// </value>
    /// <remarks>
    /// <para>
    /// Setting the level of the root logger to a <c>null</c> reference
    /// may have catastrophic results. We prevent this here.
    /// </para>
    /// </remarks>
    public override Level? Level
    {
      get => base.Level;
      set
      {
        if (value is null)
        {
          LogLog.Error(declaringType, "You have tried to set a null level to root.", new LogException());
        }
        else
        {
          base.Level = value;
        }
      }
    }

    /// <summary>
    /// The fully qualified type of the RootLogger class.
    /// </summary>
    /// <remarks>
    /// Used by the internal logger to record the Type of the
    /// log message.
    /// </remarks>
    private static readonly Type declaringType = typeof(RootLogger);
  }
}
