jspwiki-api/src/main/java/org/apache/wiki/api/filters/PageFilter.java

/* 
    Licensed to the Apache Software Foundation (ASF) under one
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    to you under the Apache License, Version 2.0 (the
    "License"); you may not use this file except in compliance
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       http://www.apache.org/licenses/LICENSE-2.0

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 */
package org.apache.wiki.api.filters;

import org.apache.wiki.api.core.Context;
import org.apache.wiki.api.core.Engine;
import org.apache.wiki.api.exceptions.FilterException;

import java.util.Properties;


/**
 *  Provides a definition for a page filter.  A page filter is a class that can be used to transform the WikiPage content being saved or
 *  being loaded at any given time.
 *  <p>
 *  Note that the WikiContext.getPage() method always returns the context in which text is rendered, i.e. the original request.  Thus the
 *  content may actually be different content than what what the wikiContext.getPage() implies!  This happens often if you are for example
 *  including multiple pages on the same page.
 *  <p>
 *  PageFilters must be thread-safe!  There is only one instance of each PageFilter per each Engine invocation.  If you need to store data
 *  persistently, use VariableManager, or WikiContext.
 *  <p>
 *  As of 2.5.30, initialize() gains access to the Engine.
 */
public interface PageFilter {

    /**
     *  Is called whenever the a new PageFilter is instantiated and reset.
     *  
     *  @param engine The Engine which owns this PageFilter
     *  @param properties The properties ripped from filters.xml.
     *  @throws FilterException If the filter could not be initialized. If this is thrown, the filter is not added to the internal queues.
     */
    void initialize( Engine engine, Properties properties ) throws FilterException;

    /**
     *  This method is called whenever a page has been loaded from the provider, but not yet been sent through the markup-translation
     *  process.  Note that you cannot do HTML translation here, because it will be escaped.
     *
     *  @param context The current context.
     *  @param content WikiMarkup.
     *  @return The modified wikimarkup content.
     *  @throws FilterException If something goes wrong.  Throwing this causes the entire page processing to be abandoned.
     */
    default String preTranslate( final Context context, final String content ) throws FilterException {
        return content;
    }

    /**
     *  This method is called after a page has been fed through the translation process, so anything you are seeing here is translated
     *  content.  If you want to do any of your own WikiMarkup2HTML translation, do it here.
     *  
     *  @param wikiContext The WikiContext.
     *  @param htmlContent The translated HTML
     *  @return The modified HTML
     *  @throws FilterException If something goes wrong.  Throwing this causes the entire page processing to be abandoned.
     */
    default String postTranslate( final Context wikiContext, final String htmlContent ) throws FilterException {
        return htmlContent;
    }

    /**
     *  This method is called before the page has been saved to the PageProvider.
     *  
     *  @param wikiContext The WikiContext
     *  @param content The wikimarkup that the user just wanted to save.
     *  @return The modified wikimarkup
     *  @throws FilterException If something goes wrong.  Throwing this causes the entire page processing to be abandoned.
     */
    default String preSave( final Context wikiContext, final String content ) throws FilterException {
        return content;
    }

    /**
     *  This method is called after the page has been successfully saved. If the saving fails for any reason, then this method will not
     *  be called.
     *  <p>
     *  Since the result is discarded from this method, this is only useful for things like counters, etc.
     *  
     *  @param wikiContext The WikiContext
     *  @param content The content which was just stored.
     *  @throws FilterException If something goes wrong.  As the page is already saved, This is just logged.
     */
    default void postSave( final Context wikiContext, final String content ) throws FilterException {}

    /**
     *  Called for every filter, e.g. on wiki engine shutdown. Use this if you have to 
     *  clean up or close global resources you allocated in the initialize() method.
     * 
     *  @param engine The Engine which owns this filter.
     *  @since 2.5.36
     */
    default void destroy( final Engine engine ) {}

}