#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;

using log4net.Core;

namespace log4net.Util.PatternStringConverters
{
  /// <summary>
  /// A Pattern converter that generates a string of random characters
  /// </summary>
  /// <remarks>
  /// <para>
  /// The converter generates a string of random characters. By default
  /// the string is length 4. This can be changed by setting the <see cref="PatternConverter.Option"/>
  /// to the string value of the length required.
  /// </para>
  /// <para>
  /// The random characters in the string are limited to uppercase letters and numbers only.
  /// </para>
  /// <para>
  /// The random number generator used by this class is not cryptographically secure.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  public sealed class RandomStringPatternConverter : PatternConverter, IOptionHandler
  {
    /// <summary>
    /// Shared random number generator
    /// </summary>
    private static readonly Random s_random = new Random();

    /// <summary>
    /// Length of random string to generate. Default length 4.
    /// </summary>
    private int m_length = 4;

    #region Implementation of IOptionHandler

    /// <summary>
    /// Initialize the converter options
    /// </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 void ActivateOptions()
    {
      string optionStr = Option;
      if (optionStr != null && optionStr.Length > 0)
      {
        int lengthVal;
        if (SystemInfo.TryParse(optionStr, out lengthVal))
        {
          m_length = lengthVal;
        }
        else
        {
          LogLog.Error(declaringType, "RandomStringPatternConverter: Could not convert Option [" + optionStr + "] to Length Int32");
        }
      }
    }

    #endregion

    /// <summary>
    /// Write a randoim string to the output
    /// </summary>
    /// <param name="writer">the writer to write to</param>
    /// <param name="state">null, state is not set</param>
    /// <remarks>
    /// <para>
    /// Write a randoim string to the output <paramref name="writer"/>.
    /// </para>
    /// </remarks>
    public override void Convert(TextWriter writer, object state)
    {
      try
      {
        lock (s_random)
        {
          for (int i = 0; i < m_length; i++)
          {
            int randValue = s_random.Next(36);

            if (randValue < 26)
            {
              // Letter
              char ch = (char)('A' + randValue);
              writer.Write(ch);
            }
            else if (randValue < 36)
            {
              // Number
              char ch = (char)('0' + (randValue - 26));
              writer.Write(ch);
            }
            else
            {
              // Should not get here
              writer.Write('X');
            }
          }
        }
      }
      catch (Exception ex)
      {
        LogLog.Error(declaringType, "Error occurred while converting.", ex);
      }
    }

    #region Private Static Fields

    /// <summary>
    /// The fully qualified type of the RandomStringPatternConverter class.
    /// </summary>
    /// <remarks>
    /// Used by the internal logger to record the Type of the
    /// log message.
    /// </remarks>
    private static readonly Type declaringType = typeof(RandomStringPatternConverter);

    #endregion Private Static Fields
  }
}