jspwiki-main/src/main/java/org/apache/wiki/references/ReferenceManager.java

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    to you under the Apache License, Version 2.0 (the
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       http://www.apache.org/licenses/LICENSE-2.0

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 */
package org.apache.wiki.references;

import org.apache.wiki.api.core.Page;
import org.apache.wiki.api.exceptions.ProviderException;
import org.apache.wiki.api.filters.PageFilter;
import org.apache.wiki.event.WikiEventListener;
import org.apache.wiki.modules.InternalModule;

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

/**
 *  Keeps track of wikipage references:
 *  <ul>
 *  <li>What pages a given page refers to</li>
 *  <li>What pages refer to a given page</li>
 *  </ul>
 *
 *  When a page is added or edited, its references are parsed, a Collection is received, and we crudely replace anything previous with
 *  this new Collection. We then check each referenced page name and make sure they know they are referred to by the new page.
 *  <p>
 *  Based on this information, we can perform non-optimal searches for e.g. unreferenced pages, top ten lists, etc.
 *  <p>
 *  The owning class must take responsibility of filling in any pre-existing information, probably by loading each and every WikiPage
 *  and calling this class to update the references when created.
 */
public interface ReferenceManager extends PageFilter, InternalModule, WikiEventListener {

    /**
     *  Initializes the entire reference manager with the initial set of pages from the collection.
     *
     *  @param pages A collection of all pages you want to be included in the reference count.
     *  @since 2.2
     *  @throws ProviderException If reading of pages fails.
     */
    void initialize( final Collection< Page > pages ) throws ProviderException;

    /**
     *  Reads a WikiPageful of data from a String and returns all links internal to this Wiki in a Collection.
     *
     *  @param page The WikiPage to scan
     *  @param pagedata The page contents
     *  @return a Collection of Strings
     */
    Collection< String > scanWikiLinks( final Page page, final String pagedata );

    /**
     * Updates the m_referedTo and m_referredBy hashmaps when a page has been deleted.
     * <P>
     * Within the m_refersTo map the pagename is a key. The whole key-value-set has to be removed to keep the map clean.
     * Within the m_referredBy map the name is stored as a value. Since a key can have more than one value we have to
     * delete just the key-value-pair referring page:deleted page.
     *
     *  @param page Name of the page to remove from the maps.
     */
    void pageRemoved( final Page page );

    /**
     *  Updates all references for the given page.
     *
     *  @param page wiki page for which references should be updated
     */
    void updateReferences( final Page page );

    /**
     *  Updates the referred pages of a new or edited WikiPage. If a refersTo entry for this page already exists, it is removed
     *  and a new one is built from scratch. Also calls updateReferredBy() for each referenced page.
     *  <P>
     *  This is the method to call when a new page has been created and we want to a) set up its references and b) notify the
     *  referred pages of the references. Use this method during run-time.
     *
     *  @param page Name of the page to update.
     *  @param references A Collection of Strings, each one pointing to a page this page references.
     */
    void updateReferences( final String page, final Collection<String> references );

    /**
     * Clears the references to a certain page so it's no longer in the map.
     *
     * @param pagename  Name of the page to clear references for.
     */
    void clearPageEntries( String pagename );


    /**
     *  Finds all unreferenced pages. This requires a linear scan through m_referredBy to locate keys with null or empty values.
     *
     *  @return The Collection of Strings
     */
    Collection< String > findUnreferenced();

    /**
     * Finds all references to non-existant pages. This requires a linear scan through m_refersTo values; each value
     * must have a corresponding key entry in the reference Maps, otherwise such a page has never been created.
     * <P>
     * Returns a Collection containing Strings of unreferenced page names. Each non-existant page name is shown only
     * once - we don't return information on who referred to it.
     *
     * @return A Collection of Strings
     */
    Collection< String > findUncreated();

    /**
     * Find all pages that refer to this page. Returns null if the page does not exist or is not referenced at all,
     * otherwise returns a collection containing page names (String) that refer to this one.
     * <p>
     * @param pagename The page to find referrers for.
     * @return A Set of Strings.  May return null, if the page does not exist, or if it has no references.
     */
    Set< String > findReferrers( String pagename );

    /**
     *  Returns all pages that refer to this page.  Note that this method returns an unmodifiable Map, which may be abruptly changed.
     *  So any access to any iterator may result in a ConcurrentModificationException.
     *  <p>
     *  The advantages of using this method over findReferrers() is that it is very fast, as it does not create a new object.
     *  The disadvantages are that it does not do any mapping between plural names, and you may end up getting a
     *  ConcurrentModificationException.
     *
     * @param pageName Page name to query.
     * @return A Set of Strings containing the names of all the pages that refer to this page.  May return null, if the page does
     *         not exist or has not been indexed yet.
     * @since 2.2.33
     */
    Set< String > findReferredBy( String pageName );

    /**
     *  Returns all pages that this page refers to.  You can use this as a quick way of getting the links from a page, but note
     *  that it does not link any InterWiki, image, or external links.  It does contain attachments, though.
     *  <p>
     *  The Collection returned is unmutable, so you cannot change it.  It does reflect the current status and thus is a live
     *  object.  So, if you are using any kind of an iterator on it, be prepared for ConcurrentModificationExceptions.
     *  <p>
     *  The returned value is a Collection, because a page may refer to another page multiple times.
     *
     * @param pageName Page name to query
     * @return A Collection of Strings containing the names of the pages that this page refers to. May return null, if the page
     *         does not exist or has not been indexed yet.
     * @since 2.2.33
     */
    Collection< String > findRefersTo( String pageName );

    /**
     *  Returns a list of all pages that the ReferenceManager knows about. This should be roughly equivalent to
     *  PageManager.getAllPages(), but without the potential disk access overhead.  Note that this method is not guaranteed
     *  to return a Set of really all pages (especially during startup), but it is very fast.
     *
     *  @return A Set of all defined page names that ReferenceManager knows about.
     *  @since 2.3.24
     */
    Set< String > findCreated();

}