#region Apache License
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//
// http://www.apache.org/licenses/LICENSE-2.0
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using log4net.Core;

namespace log4net.Filter;

/// <summary>
/// Subclass this type to implement customized logging event filtering
/// </summary>
/// <remarks>
/// <para>
/// Users should extend this class to implement customized logging
/// event filtering. Note that <see cref="log4net.Repository.Hierarchy.Logger"/> and 
/// <see cref="log4net.Appender.AppenderSkeleton"/>, the parent class of all standard
/// appenders, have built-in filtering rules. It is suggested that you
/// first use and understand the built-in rules before rushing to write
/// your own custom filters.
/// </para>
/// <para>
/// This abstract class assumes and also imposes that filters be
/// organized in a linear chain. The <see cref="Decide"/>
/// method of each filter is called sequentially, in the order of their 
/// addition to the chain.
/// </para>
/// <para>
/// The <see cref="Decide"/> method must return one
/// of the integer constants <see cref="FilterDecision.Deny"/>, 
/// <see cref="FilterDecision.Neutral"/> or <see cref="FilterDecision.Accept"/>.
/// </para>
/// <para>
/// If the value <see cref="FilterDecision.Deny"/> is returned, then the log event is dropped 
/// immediately without consulting with the remaining filters.
/// </para>
/// <para>
/// If the value <see cref="FilterDecision.Neutral"/> is returned, then the next filter
/// in the chain is consulted. If there are no more filters in the
/// chain, then the log event is logged. Thus, in the presence of no
/// filters, the default behavior is to log all logging events.
/// </para>
/// <para>
/// If the value <see cref="FilterDecision.Accept"/> is returned, then the log
/// event is logged without consulting the remaining filters.
/// </para>
/// <para>
/// The philosophy of log4net filters is largely inspired from the
/// Linux ipchains.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
/// <author>Gert Driesen</author>
public abstract class FilterSkeleton : IFilter
{
  /// <summary>
  /// Initialize the filter with the options set
  /// </summary>
  /// <remarks>
  /// <para>
  /// This is part of the <see cref="IOptionHandler"/> delayed object
  /// activation scheme. The <see cref="ActivateOptions"/> method must 
  /// be called on this object after the configuration properties have
  /// been set. Until <see cref="ActivateOptions"/> is called this
  /// object is in an undefined state and must not be used. 
  /// </para>
  /// <para>
  /// If any of the configuration properties are modified then 
  /// <see cref="ActivateOptions"/> must be called again.
  /// </para>
  /// <para>
  /// Typically filter's options become active immediately on set, 
  /// however this method must still be called. 
  /// </para>
  /// </remarks>
  public virtual void ActivateOptions()
  {
  }

  /// <summary>
  /// Decide if the <see cref="LoggingEvent"/> should be logged through an appender.
  /// </summary>
  /// <param name="loggingEvent">The <see cref="LoggingEvent"/> to decide upon</param>
  /// <returns>The decision of the filter</returns>
  /// <remarks>
  /// <para>
  /// If the decision is <see cref="FilterDecision.Deny"/>, then the event will be
  /// dropped. If the decision is <see cref="FilterDecision.Neutral"/>, then the next
  /// filter, if any, will be invoked. If the decision is <see cref="FilterDecision.Accept"/> then
  /// the event will be logged without consulting with other filters in
  /// the chain.
  /// </para>
  /// <para>
  /// This method is marked <c>abstract</c> and must be implemented
  /// in a subclass.
  /// </para>
  /// </remarks>
  public abstract FilterDecision Decide(LoggingEvent loggingEvent);

  /// <summary>
  /// Gets or sets the next filter in the filter chain.
  /// </summary>
  /// <remarks>
  /// <para>
  /// Filters are typically composed into chains. This property allows the next filter in 
  /// the chain to be accessed.
  /// </para>
  /// </remarks>
  public IFilter? Next { get; set; }
}
