#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");
  }
}