#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.IO;
using System.Collections;
using System.Configuration;
using System.Collections.Generic;

namespace log4net.Util.PatternStringConverters
{
  /// <summary>
  /// AppSetting pattern converter
  /// </summary>
  /// <remarks>
  /// <para>
  /// This pattern converter reads appSettings from the application configuration file.
  /// </para>
  /// <para>
  /// If the <see cref="PatternConverter.Option"/> is specified then that will be used to
  /// lookup a single appSettings value. If no <see cref="PatternConverter.Option"/> is specified
  /// then all appSettings will be dumped as a list of key value pairs.
  /// </para>
  /// <para>
  /// A typical use is to specify a base directory for log files, e.g.
  /// <example>
  /// <![CDATA[
  /// <log4net>
  ///    <appender name="MyAppender" type="log4net.Appender.RollingFileAppender">
  ///      <file type="log4net.Util.PatternString" value="appsetting{LogDirectory}MyApp.log"/>
  ///       ...
  ///   </appender>
  /// </log4net>
  /// ]]>
  /// </example>
  /// </para>
  /// </remarks>
  internal sealed class AppSettingPatternConverter : PatternConverter
  {
    private static IDictionary AppSettingsDictionary
    {
      get
      {
        if (_appSettingsHashTable is null)
        {
          var h = new Dictionary<string, string?>();
          foreach (string key in ConfigurationManager.AppSettings)
          {
            h.Add(key, ConfigurationManager.AppSettings[key]);
          }
          _appSettingsHashTable = h;
        }
        return _appSettingsHashTable;
      }

    }
    private static Dictionary<string, string?>? _appSettingsHashTable;

    /// <summary>
    /// Write the property value to the output
    /// </summary>
    /// <param name="writer"><see cref="TextWriter" /> that will receive the formatted result.</param>
    /// <param name="state">null, state is not set</param>
    /// <remarks>
    /// <para>
    /// Writes out the value of a named property. The property name
    /// should be set in the <see cref="log4net.Util.PatternConverter.Option"/>
    /// property.
    /// </para>
    /// <para>
    /// If the <see cref="log4net.Util.PatternConverter.Option"/> is set to <c>null</c>
    /// then all the properties are written as key value pairs.
    /// </para>
    /// </remarks>
    public override void Convert(TextWriter writer, object? state)
    {
      if (Option is not null)
      {
        // Write the value for the specified key
        WriteObject(writer, null, ConfigurationManager.AppSettings[Option]);
      }
      else
      {
        // Write all the key value pairs
        WriteDictionary(writer, null, AppSettingsDictionary);
      }
    }
  }
}