#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.Diagnostics;
using System.IO;
using log4net.Core;

namespace log4net.Layout.Pattern
{
  /// <summary>
  /// Write the exception text to the output
  /// </summary>
  /// <remarks>
  /// <para>
  /// If an exception object is stored in the logging event
  /// it will be rendered into the pattern output with a
  /// trailing newline.
  /// </para>
  /// <para>
  /// If there is no exception then nothing will be output
  /// and no trailing newline will be appended.
  /// It is typical to put a newline before the exception
  /// and to have the exception as the last data in the pattern.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  internal sealed class ExceptionPatternConverter : PatternLayoutConverter
  {
    /// <summary>
    /// Default constructor
    /// </summary>
    public ExceptionPatternConverter()
    {
      // This converter handles the exception
      IgnoresException = false;
    }

    /// <summary>
    /// Write the exception text to the output
    /// </summary>
    /// <param name="writer"><see cref="TextWriter" /> that will receive the formatted result.</param>
    /// <param name="loggingEvent">the event being logged</param>
    /// <remarks>
    /// <para>
    /// If an exception object is stored in the logging event
    /// it will be rendered into the pattern output with a
    /// trailing newline.
    /// </para>
    /// <para>
    /// If there is no exception or the exception property specified
    /// by the Option value does not exist then nothing will be output
    /// and no trailing newline will be appended.
    /// It is typical to put a newline before the exception
    /// and to have the exception as the last data in the pattern.
    /// </para>
    /// <para>
    /// Recognized values for the Option parameter are:
    /// </para>
    /// <list type="bullet">
    ///    <item>
    ///      <description>Message</description>
    ///    </item>
    ///    <item>
    ///      <description>Source</description>
    ///    </item>
    ///    <item>
    ///      <description>StackTrace</description>
    ///    </item>
    ///    <item>
    ///      <description>TargetSite</description>
    ///    </item>
    ///    <item>
    ///      <description>HelpLink</description>
    ///    </item>    
    /// </list>
    /// </remarks>
    protected override void Convert(TextWriter writer, LoggingEvent loggingEvent)
    {
      if (loggingEvent.ExceptionObject is not null && !string.IsNullOrEmpty(Option))
      {
        switch (Option!.ToLowerInvariant())
        {
          case "message":
            WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.Message);
            break;
          case "source":
            WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.Source);
            break;
          case "stacktrace":
            WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.StackTrace);
            break;
          case "targetsite":
            WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.TargetSite);
            break;
          case "helplink":
            WriteObject(writer, loggingEvent.Repository, loggingEvent.ExceptionObject.HelpLink);
            break;
          default:
            // do not output SystemInfo.NotAvailableText
            break;
        }
      }
      else
      {
        string? exceptionString = loggingEvent.GetExceptionString();
        if (!string.IsNullOrEmpty(exceptionString))
        {
          writer.WriteLine(exceptionString);
        }
        else
        {
          // do not output SystemInfo.NotAvailableText
        }
      }
    }
  }
}
