#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.Collections.Generic;
using System.Linq;
using log4net.Core;

namespace log4net.Util
{
  /// <summary>
  /// Manages an ordered mapping from <see cref="Level"/> instances 
  /// to <see cref="LevelMappingEntry"/> subclasses.
  /// </summary>
  /// <author>Nicko Cadell</author>
  public sealed class LevelMapping : IOptionHandler
  {
    private readonly Dictionary<Level, LevelMappingEntry> entries = new();
    private List<LevelMappingEntry>? sortedEntries;

    /// <summary>
    /// Add a <see cref="LevelMappingEntry"/> to this mapping
    /// </summary>
    /// <param name="entry">the entry to add</param>
    /// <remarks>
    /// <para>
    /// If a <see cref="LevelMappingEntry"/> has previously been added
    /// for the same <see cref="Level"/> then that entry will be 
    /// overwritten.
    /// </para>
    /// </remarks>
    public void Add(LevelMappingEntry entry)
    {
      if (entry.Level is not null)
      {
        entries[entry.Level] = entry;
      }
    }

    /// <summary>
    /// Looks up the value for the specified level. Finds the nearest
    /// mapping value for the level that is equal to or less than the
    /// <paramref name="level"/> specified.
    /// </summary>
    /// <param name="level">the level to look up.</param>
    /// <returns>The <see cref="LevelMappingEntry"/> for the level or <see langword="null"/> if no mapping found</returns>
    public LevelMappingEntry? Lookup(Level? level)
    {
      if (level is null || sortedEntries is null)
      {
        return null;
      }

      foreach (LevelMappingEntry entry in sortedEntries)
      {
        if (level >= entry.Level)
        {
          return entry;
        }
      }
      return null;
    }

    /// <summary>
    /// Initialize options
    /// </summary>
    /// <remarks>
    /// Caches the sorted list of <see cref="LevelMappingEntry"/>
    /// </remarks>
    public void ActivateOptions()
    {
      sortedEntries = SortEntries();
      sortedEntries.ForEach(entry => entry.ActivateOptions());
    }

    private List<LevelMappingEntry> SortEntries()
      => entries.OrderByDescending(entry => entry.Key).Select(entry => entry.Value).ToList();
  }
}