src/log4net/Layout/DynamicPatternLayout.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;

namespace log4net.Layout;

/// <summary>
/// A flexible layout configurable with pattern string that re-evaluates on each call.
/// </summary>
/// <remarks>
/// <para>This class is built on <see cref="PatternLayout"></see> and provides all the
/// features and capabilities of PatternLayout.  PatternLayout is a 'static' class
/// in that its layout is done once at configuration time.  This class will recreate
/// the layout on each reference.</para>
/// <para>One important difference between PatternLayout and DynamicPatternLayout is the
/// treatment of the Header and Footer parameters in the configuration.  The Header and Footer
/// parameters for DynamicPatternLayout must be syntactically in the form of a PatternString,
/// but should not be marked as type log4net.Util.PatternString.  Doing so causes the
/// pattern to be statically converted at configuration time and causes DynamicPatternLayout
/// to perform the same as PatternLayout.</para>
/// <para>Please see <see cref="PatternLayout"/> for complete documentation.</para>
/// <example>
///  &lt;layout type="log4net.Layout.DynamicPatternLayout"&gt;
///   &lt;param name="Header" value="%newline**** Trace Opened     Local: %date{yyyy-MM-dd HH:mm:ss.fff}     UTC: %utcdate{yyyy-MM-dd HH:mm:ss.fff} ****%newline" /&gt;
///   &lt;param name="Footer" value="**** Trace Closed %date{yyyy-MM-dd HH:mm:ss.fff} ****%newline" /&gt;
/// &lt;/layout&gt;
/// </example>
/// </remarks>
public class DynamicPatternLayout : PatternLayout
{
  /// <summary>
  /// The header PatternString
  /// </summary>
  private PatternString _headerPatternString = new(string.Empty);

  /// <summary>
  /// The footer PatternString
  /// </summary>
  private PatternString _footerPatternString = new(string.Empty);

  /// <summary>
  /// Constructs a DynamicPatternLayout using the DefaultConversionPattern
  /// </summary>
  /// <remarks>
  /// <para>
  /// The default pattern just produces the application supplied message.
  /// </para>
  /// </remarks>
  public DynamicPatternLayout()
    : base()
  {
  }

  /// <summary>
  /// Constructs a DynamicPatternLayout using the supplied conversion pattern.
  /// </summary>
  /// <param name="pattern">The pattern to use.</param>
  public DynamicPatternLayout(string pattern)
    : base(pattern)
  {
  }

  /// <summary>
  /// Gets or sets the header for the layout format.
  /// </summary>
  /// <value>the layout header</value>
  /// <remarks>
  /// <para>
  /// The Header text will be appended before any logging events
  /// are formatted and appended.
  /// </para>
  /// The pattern will be formatted on each get operation.
  /// </remarks>
  public override string? Header
  {
    get => _headerPatternString.Format();
    set
    {
      base.Header = value;
      if (value is not null)
      {
        _headerPatternString = new PatternString(value);
      }
    }
  }

  /// <summary>
  /// Gets or sets the footer for the layout format.
  /// </summary>
  /// <value>the layout footer</value>
  /// <remarks>
  /// <para>
  /// The Footer text will be appended after all the logging events
  /// have been formatted and appended.
  /// </para>
  /// The pattern will be formatted on each get operation.
  /// </remarks>
  public override string? Footer
  {
    get => _footerPatternString.Format();
    set
    {
      base.Footer = value;
      _footerPatternString = new PatternString(value);
    }
  }
}