/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.spi;


import ch.qos.logback.core.CoreConstants;

import java.util.Collection;
import java.util.Set;

/**
 * Interface for tracking various components by key. Components which have not
 * been accessed for more than a user-specified duration are deemed stale and
 * removed. Components can also be explicitly marked as having reached their
 * {@link #endOfLife(String)} in which case they will linger for a few seconds
 * and then be removed.
 *
 * @author Tommy Becker
 * @author Ceki Gulcu
 * @author David Roussel
 *
 * @since 1.0.12
 */
public interface ComponentTracker<C> {

  /**
   * The default timeout duration is 30 minutes
   */
  public final int DEFAULT_TIMEOUT = 30 * 60 * CoreConstants.MILLIS_IN_ONE_SECOND; // 30 minutes

  /**
   * By default an unlimited number of elements can be tracked.
   */
  int DEFAULT_MAX_COMPONENTS = Integer.MAX_VALUE;

  /**
   * Returns the number of components tracked.
   * @return number of components
   */
  int getComponentCount();


  /**
   * Find the component identified by 'key', without updating the timestamp. Returns null if no
   * corresponding component could be found.
   *
   * @param key
   * @return corresponding component, may be null
   */
  C find(String key);

  /**
   * Get the component identified by 'key', updating its timestamp in the
   * process. If the corresponding component could not be found, it is created.
   *
   * @param key
   * @param timestamp
   * @return
   */
  C getOrCreate(String key, long timestamp);


  /**
   * Remove components which are deemed stale. Components which have not
   * been accessed for more than a user-specified duration are deemed stale.
   *
   * <p>If the number of components exceeds, {@link #getComponentCount()},
   * components in excess will be removed.</p>
   *
   * <p>Depending on the component type, components will be cleared or stopped
   * (as appropriate) right before removal.</p>
   *
   * @param now  current time in milliseconds
   */
  void removeStaleComponents(long now);


  /**
   * Mark component identified by 'key' as having reached its end-of-life. End-of-lifed
   * components will linger for a few more seconds before being removed.
   *
   * @param key
   */
  void endOfLife(String key);

  /**
   * Returns the collection of all components tracked by this instance.
   * @return  collection of components
   */
  Collection<C> allComponents();


  /**
   * Set of all keys in this tracker in no particular order.
   *
   * @return
   */
  Set<String> allKeys();
}
