#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.IO;

namespace log4net.Util.PatternStringConverters;

/// <summary>
/// Pattern converter for literal string instances in the pattern
/// </summary>
/// <remarks>
/// <para>
/// Writes the literal string value specified in the 
/// <see cref="log4net.Util.PatternConverter.Option"/> property to 
/// the output.
/// </para>
/// </remarks>
/// <author>Nicko Cadell</author>
internal class LiteralPatternConverter : PatternConverter
{
  /// <summary>
  /// Set the next converter in the chain
  /// </summary>
  /// <param name="pc">The next pattern converter in the chain</param>
  /// <returns>The next pattern converter</returns>
  /// <remarks>
  /// <para>
  /// Special case the building of the pattern converter chain
  /// for <see cref="LiteralPatternConverter"/> instances. Two adjacent
  /// literals in the pattern can be represented by a single combined
  /// pattern converter. This implementation detects when a 
  /// <see cref="LiteralPatternConverter"/> is added to the chain
  /// after this converter and combines its value with this converter's
  /// literal value.
  /// </para>
  /// </remarks>
  public override PatternConverter SetNext(PatternConverter pc)
  {
    if (pc is LiteralPatternConverter literalPc)
    {
      // Combine the two adjacent literals together
      Option += literalPc.Option;
      // We are the next converter now
      return this;
    }

    return base.SetNext(pc);
  }

  /// <summary>
  /// Write the literal to the output
  /// </summary>
  /// <param name="writer">the writer to write to</param>
  /// <param name="state">null, not set</param>
  /// <remarks>
  /// <para>
  /// Override the formatting behavior to ignore the FormattingInfo
  /// because we have a literal instead.
  /// </para>
  /// <para>
  /// Writes the value of <see cref="log4net.Util.PatternConverter.Option"/>
  /// to the output <paramref name="writer"/>.
  /// </para>
  /// </remarks>
  public override void Format(TextWriter writer, object? state)
    => writer.Write(Option);

  /// <summary>
  /// Convert this pattern into the rendered message
  /// </summary>
  /// <param name="writer"><see cref="TextWriter" /> that will receive the formatted result.</param>
  /// <param name="state">null, not set</param>
  /// <remarks>
  /// <para>
  /// This method is not used.
  /// </para>
  /// </remarks>
  public override void Convert(TextWriter writer, object? state)
    => throw new InvalidOperationException("Should never get here because of the overridden Format method");
}