#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 <see langword="null"/>
/// 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 <see langword="null"/> 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 <see langword="null"/> 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);
}
