#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;
using System.IO;

using log4net.Util;
using log4net.DateFormatter;
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>
	internal 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>
		protected 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
	}
}