CacheKey.cs :  » Persistence-Frameworks » iBATIS.NET » IBatisNet » DataMapper » Configuration » Cache » C# / CSharp Open Source

#region Apache Notice
/*****************************************************************************
 * $Header: $
 * $Revision: 451064 $
 * $Date: 2006-09-29 01:53:56 +0200 (ven., 29 sept. 2006) $
 * 
 * iBATIS.NET Data Mapper
 * Copyright (C) 2005 - iBATIS Team
 *  
 * 
 * Licensed 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.Collections;
using System.Text;

namespace IBatisNet.DataMapper.Configuration.Cache{
  using IBatisNet.Common.Utilities;

  /// <summary>
  ///  Hash value generator for cache keys
  /// </summary>
  public class CacheKey
  {
    private const int DEFAULT_MULTIPLYER = 37;
    private const int DEFAULT_HASHCODE = 17;

    private int _multiplier = DEFAULT_MULTIPLYER;
    private int _hashCode = DEFAULT_HASHCODE;
    private long _checksum = long.MinValue;
    private int _count = 0;
    private IList _paramList = new ArrayList();

    /// <summary>
    /// Default constructor
    /// </summary>
    public CacheKey()
    {
      _hashCode = DEFAULT_HASHCODE;
      _multiplier = DEFAULT_MULTIPLYER;
      _count = 0;
    }

    /// <summary>
    /// Constructor that supplies an initial hashcode
    /// </summary>
    /// <param name="initialNonZeroOddNumber">the hashcode to use</param>
    public CacheKey(int initialNonZeroOddNumber) 
    {
      _hashCode = initialNonZeroOddNumber;
      _multiplier = DEFAULT_MULTIPLYER;
      _count = 0;
    }

    /// <summary>
    /// Constructor that supplies an initial hashcode and multiplier
    /// </summary>
    /// <param name="initialNonZeroOddNumber">the hashcode to use</param>
    /// <param name="multiplierNonZeroOddNumber">the multiplier to use</param>
    public CacheKey(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber) 
    {
      _hashCode = initialNonZeroOddNumber;
      _multiplier = multiplierNonZeroOddNumber;
      _count = 0;
    }

    /// <summary>
    /// Updates this object with new information based on an object
    /// </summary>
    /// <param name="obj">the object</param>
    /// <returns>the cachekey</returns>
    public CacheKey Update(object obj) 
    {
      int baseHashCode = HashCodeProvider.GetIdentityHashCode(obj);

      _count++;
      _checksum += baseHashCode;
      baseHashCode *= _count;

      _hashCode = _multiplier * _hashCode + baseHashCode;

      _paramList.Add(obj);

      return this;
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public override bool Equals(object obj) 
    {
      if (this == obj) return true;
      if (!(obj is CacheKey)) return false;

      CacheKey cacheKey = (CacheKey) obj;

      if (_hashCode != cacheKey._hashCode) return false;
      if (_checksum != cacheKey._checksum) return false;
      if (_count != cacheKey._count) return false;

      int count = _paramList.Count;
      for (int i=0; i < count; i++) 
      {
        object thisParam = _paramList[i];
        object thatParam = cacheKey._paramList[i];
        if(thisParam == null) 
        {
          if (thatParam != null) return false;
        } 
        else 
        {
          if (!thisParam.Equals(thatParam)) return false;
        }
      }

      return true;
    }

    /// <summary>
    /// Get the HashCode for this CacheKey
    /// </summary>
    /// <returns></returns>
    public override int GetHashCode() 
    {
      return _hashCode;
    }

    /// <summary>
    /// ToString implementation.
    /// </summary>
    /// <returns>A string that give the CacheKey HashCode.</returns>
    public override string ToString() 
    {
      return new StringBuilder().Append(_hashCode).Append('|').Append(_checksum).ToString();
    }

  }
}