#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.RegularExpressions;

using log4net.Core;

namespace log4net.Filter;

/// <summary>
/// Simple filter to match a string in the rendered message.
/// </summary>
/// <author>Nicko Cadell</author>
/// <author>Gert Driesen</author>
public class StringMatchFilter : FilterSkeleton
{
  /// <summary>
  /// A regex object to match (generated from m_stringRegexToMatch)
  /// </summary>
  // ReSharper disable once InconsistentNaming
  protected Regex? m_regexToMatch;

  /// <summary>
  /// Initialize and precompile the Regex if required
  /// </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>
  /// </remarks>
  public override void ActivateOptions() 
  {
    if (RegexToMatch is not null)
    {
      m_regexToMatch = new(RegexToMatch, RegexOptions.Compiled);
    }
  }

  /// <summary>
  /// <see cref="FilterDecision.Accept"/> when matching <see cref="StringToMatch"/> or <see cref="RegexToMatch"/>
  /// </summary>
  /// <remarks>
  /// <para>
  /// The <see cref="AcceptOnMatch"/> property is a flag that determines
  /// the behavior when a matching <see cref="Level"/> is found. If the
  /// flag is set to true then the filter will <see cref="FilterDecision.Accept"/> the 
  /// logging event, otherwise it will <see cref="FilterDecision.Neutral"/> the event.
  /// </para>
  /// <para>
  /// The default is <c>true</c> i.e. to <see cref="FilterDecision.Accept"/> the event.
  /// </para>
  /// </remarks>
  public bool AcceptOnMatch { get; set; } = true;

  /// <summary>
  /// Sets the static string to match
  /// </summary>
  /// <remarks>
  /// <para>
  /// The string that will be substring matched against
  /// the rendered message. If the message contains this
  /// string then the filter will match. If a match is found then
  /// the result depends on the value of <see cref="AcceptOnMatch"/>.
  /// </para>
  /// <para>
  /// One of <see cref="StringToMatch"/> or <see cref="RegexToMatch"/>
  /// must be specified.
  /// </para>
  /// </remarks>
  public string? StringToMatch { get; set; }

  /// <summary>
  /// Sets the regular expression to match
  /// </summary>
  /// <remarks>
  /// <para>
  /// The regular expression pattern that will be matched against
  /// the rendered message. If the message matches this
  /// pattern then the filter will match. If a match is found then
  /// the result depends on the value of <see cref="AcceptOnMatch"/>.
  /// </para>
  /// <para>
  /// One of <see cref="StringToMatch"/> or <see cref="RegexToMatch"/>
  /// must be specified.
  /// </para>
  /// </remarks>
  public string? RegexToMatch { get; set; }

  /// <summary>
  /// Check if this filter should allow the event to be logged
  /// </summary>
  /// <param name="loggingEvent">the event being logged</param>
  /// <returns>see remarks</returns>
  /// <remarks>
  /// <para>
  /// The rendered message is matched against the <see cref="StringToMatch"/>.
  /// If the <see cref="StringToMatch"/> occurs as a substring within
  /// the message then a match will have occurred. If no match occurs
  /// this function will return <see cref="FilterDecision.Neutral"/>
  /// allowing other filters to check the event. If a match occurs then
  /// the value of <see cref="AcceptOnMatch"/> is checked. If it is
  /// true then <see cref="FilterDecision.Accept"/> is returned otherwise
  /// <see cref="FilterDecision.Deny"/> is returned.
  /// </para>
  /// </remarks>
  public override FilterDecision Decide(LoggingEvent loggingEvent) 
  {
    if (loggingEvent is null)
    {
      throw new ArgumentNullException(nameof(loggingEvent));
    }

    string? msg = loggingEvent.RenderedMessage;

    // Check if we have been setup to filter
    if (msg is null || (StringToMatch is null && m_regexToMatch is null))
    {
      // We cannot filter so allow the filter chain
      // to continue processing
      return FilterDecision.Neutral;
    }
  
    // Firstly check if we are matching using a regex
    if (m_regexToMatch is not null)
    {
      // Check the regex
      if (m_regexToMatch.Match(msg).Success == false)
      {
        // No match, continue processing
        return FilterDecision.Neutral;
      } 

      // we've got a match
      if (AcceptOnMatch) 
      {
        return FilterDecision.Accept;
      } 
      return FilterDecision.Deny;
    }
    else if (StringToMatch is not null)
    {
      // Check substring match
      if (msg.IndexOf(StringToMatch) == -1) 
      {
        // No match, continue processing
        return FilterDecision.Neutral;
      } 

      // we've got a match
      if (AcceptOnMatch) 
      {
        return FilterDecision.Accept;
      } 
      return FilterDecision.Deny;
    }

    return FilterDecision.Neutral;
  }
}
