src/log4net/DateFormatter/AbsoluteTimeDateFormatter.cs

#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 log4net.Util;
using System;
using System.Collections.Concurrent;
using System.IO;
using System.Text;

namespace log4net.DateFormatter;

/// <summary>
/// Formats a <see cref="DateTime"/> as <c>"HH:mm:ss,fff"</c>.
/// </summary>
/// <remarks>
/// <para>
/// Formats a <see cref="DateTime"/> in the format <c>"HH:mm:ss,fff"</c> for example, <c>"15:49:37,459"</c>.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
/// <author>Gert Driesen</author>
public class AbsoluteTimeDateFormatter : IDateFormatter
{
  private readonly record struct TimeString(long TimeToTheSecond, string AsString);

  /// <summary>
  /// Renders the date into a string. Format is <c>"HH:mm:ss"</c>.
  /// </summary>
  /// <param name="dateToFormat">The date to render into a string.</param>
  /// <param name="buffer">The string builder to write to.</param>
  /// <remarks>
  /// <para>
  /// Subclasses should override this method to render the date
  /// into a string using a precision up to the second. This method
  /// will be called at most once per second and the result will be
  /// reused if it is needed again during the same second.
  /// </para>
  /// </remarks>
  protected virtual void FormatDateWithoutMillis(DateTime dateToFormat, StringBuilder buffer)
  {
    buffer.EnsureNotNull();
    int hour = dateToFormat.Hour;
    if (hour < 10)
    {
      buffer.Append('0');
    }
    buffer.Append(hour).Append(':');

    int mins = dateToFormat.Minute;
    if (mins < 10)
    {
      buffer.Append('0');
    }
    buffer.Append(mins).Append(':');

    int secs = dateToFormat.Second;
    if (secs < 10)
    {
      buffer.Append('0');
    }
    buffer.Append(secs);
  }

  /// <summary>
  /// Renders the date into a string. Format is "HH:mm:ss,fff".
  /// </summary>
  /// <param name="dateToFormat">The date to render into a string.</param>
  /// <param name="writer">The writer to write to.</param>
  /// <remarks>
  /// <para>
  /// Uses the <see cref="FormatDateWithoutMillis"/> method to generate the
  /// time string up to the seconds and then appends the current
  /// milliseconds. The results from <see cref="FormatDateWithoutMillis"/> are
  /// cached and <see cref="FormatDateWithoutMillis"/> is called at most once
  /// per second.
  /// </para>
  /// <para>
  /// Subclasses should override <see cref="FormatDateWithoutMillis"/>
  /// rather than <see cref="FormatDate"/>.
  /// </para>
  /// </remarks>
  public virtual void FormatDate(DateTime dateToFormat, TextWriter writer)
  {
    // Calculate the current time precise only to the second
    long timeToTheSecond = dateToFormat.Ticks - (dateToFormat.Ticks % TimeSpan.TicksPerSecond);
    // Compare this time with the stored last time
    // If we are in the same second then append the previously calculated time string
    if (!_sLastTimeStrings.TryGetValue(GetType(), out TimeString timeString) || timeString.TimeToTheSecond != timeToTheSecond)
    {
      timeString = BuildTimeString(dateToFormat, timeToTheSecond);
      _sLastTimeStrings[GetType()] = timeString;
    }
    writer.EnsureNotNull().Write(timeString.AsString);

    // Append the current millisecond info
    writer.Write(',');
    int millis = dateToFormat.Millisecond;
    if (millis < 100)
    {
      writer.Write('0');
    }
    if (millis < 10)
    {
      writer.Write('0');
    }
    writer.Write(millis);

  }

  private TimeString BuildTimeString(DateTime dateToFormat, long timeToTheSecond)
  {
    StringBuilder sb = new();
    FormatDateWithoutMillis(dateToFormat, sb);
    return new(timeToTheSecond, sb.ToString());
  }

  /// <summary>
  /// String constant used to specify AbsoluteTimeDateFormat in layouts. Current value is <b>ABSOLUTE</b>.
  /// </summary>
  public const string AbsoluteTimeDateFormat = "ABSOLUTE";

  /// <summary>
  /// String constant used to specify DateTimeDateFormat in layouts.  Current value is <b>DATE</b>.
  /// </summary>
  public const string DateAndTimeDateFormat = "DATE";

  /// <summary>
  /// String constant used to specify ISO8601DateFormat in layouts. Current value is <b>ISO8601</b>.
  /// </summary>
  public const string Iso8601TimeDateFormat = "ISO8601";

  /// <summary>
  /// Last stored time with precision up to the second, formatted
  /// as a string.
  /// </summary>
  private static readonly ConcurrentDictionary<Type, TimeString> _sLastTimeStrings = new();
}