#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 System.Text;
using System.IO;

using log4net.Core;

namespace log4net.Layout.Pattern
{
  /// <summary>
  /// Converter to output the relative time of the event
  /// </summary>
  /// <remarks>
  /// <para>
  /// Converter to output the time of the event relative to the start of the program.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  internal sealed class RelativeTimePatternConverter : PatternLayoutConverter
  {
    /// <summary>
    /// Write the relative time 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>
    /// Writes out the relative time of the event in milliseconds.
    /// That is the number of milliseconds between the event <see cref="LoggingEvent.TimeStamp"/>
    /// and the <see cref="LoggingEvent.StartTime"/>.
    /// </para>
    /// </remarks>
    protected override void Convert(TextWriter writer, LoggingEvent loggingEvent)
    {
      writer.Write(TimeDifferenceInMillis(LoggingEvent.StartTimeUtc, loggingEvent.TimeStampUtc).ToString(System.Globalization.NumberFormatInfo.InvariantInfo));
    }

    /// <summary>
    /// Helper method to get the time difference between two DateTime objects
    /// </summary>
    /// <param name="start">start time (in the current local time zone)</param>
    /// <param name="end">end time (in the current local time zone)</param>
    /// <returns>the time difference in milliseconds</returns>
    private static long TimeDifferenceInMillis(DateTime start, DateTime end)
    {
      // We must convert all times to UTC before performing any mathematical
      // operations on them. This allows use to take into account discontinuities
      // caused by daylight savings time transitions.
      return (long)(end.ToUniversalTime() - start.ToUniversalTime()).TotalMilliseconds;
    }
  }
}
