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/*
 * This file is part of the DiffX library.
 *
 * For licensing information please see the file license.txt included in the release.
 * A copy of this licence can also be found at
 *   http://www.opensource.org/licenses/artistic-license-2.0.php
 */
package com.topologi.diffx.event.impl;

import java.io.IOException;

import com.topologi.diffx.event.AttributeEvent;
import com.topologi.diffx.event.DiffXEvent;
import com.topologi.diffx.xml.XMLWriter;

/**
 * A basic implementation of the attribute event.
 *
 * 
 * This implementation is not namespace aware.
 *
 * @author Christophe Lauret
 * @author Jean-Baptiste Reure
 * @version 28 March 2010
 */
public final class AttributeEventImpl extends DiffXEventBase implements AttributeEvent {

  /**
   * The name of the attribute.
   */
  private final String name;

  /**
   * The value of the attribute.
   */
  private final String value;

  /**
   * A suitable hashcode value.
   */
  private final int hashCode;

  /**
   * Creates a new attribute event.
   *
   * @param name The local name of the attribute.
   * @param value The value of the attribute.
   *
   * @throws NullPointerException if any of the argument is null.
   */
  public AttributeEventImpl(String name, String value) throws NullPointerException {
    if (name == null)
      throw new NullPointerException("Attribute must have a name.");
    if (value == null)
      throw new NullPointerException("The attribute value cannot be null, use \"\".");
    this.name = name;
    this.value = value;
    this.hashCode = toHashCode(name, value);
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public String getName() {
    return this.name;
  }

  /**
   * Always return null.
   *
   * {@inheritDoc}
   */
  @Override
  public String getURI() {
    return null;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public String getValue() {
    return this.value;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public int hashCode() {
    return this.hashCode;
  }

  /**
   * Returns true if the event is an attribute event.
   *
   * @param e The event to compare with this event.
   *
   * @return true if this event is equal to the specified event;
   *         false otherwise.
   */
  @Override
  public boolean equals(DiffXEvent e) {
    if (e.getClass() != this.getClass())
      return false;
    AttributeEventImpl bae = (AttributeEventImpl) e;
    return bae.name.equals(this.name) && bae.value.equals(this.value);
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public String toString() {
    return "attribute: " + this.name + "=" + this.value;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public void toXML(XMLWriter xml) throws IOException {
    xml.attribute(this.name, this.value);
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public StringBuffer toXML(StringBuffer xml) throws NullPointerException {
    xml.append(' ');
    xml.append(this.name);
    xml.append("=\"");
    xml.append(ESC.toAttributeValue(this.value));
    xml.append('"');
    return xml;
  }

  /**
   * Calculates the hashcode for this event.
   *
   * @param name The attribute name.
   * @param value The attribute value.
   * @return a number suitable as a hashcode.
   */
  private static int toHashCode(String name, String value) {
    int hash = 23;
    hash = hash * 37 + (name != null ? name.hashCode() : 0);
    hash = hash * 37 + (value != null ? value.hashCode() : 0);
    return hash;
  }

}