package uk.ac.omii.springweb.jspwiki;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Properties;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.log4j.Logger;

import com.ecyrd.jspwiki.WikiContext;
import com.ecyrd.jspwiki.WikiEngine;
import com.ecyrd.jspwiki.auth.permissions.PagePermission;
import com.ecyrd.jspwiki.filters.BasicPageFilter;
import com.ecyrd.jspwiki.filters.FilterException;

public class ACLFilter extends BasicPageFilter {
	private static final Logger logger = Logger.getLogger(ACLFilter.class);
	
	/*
	 * Reluctant quantifier: choose the shortest match.
	 * (?s): DOTALL mode: "." includes line terminator as well.
	 */
	private static final String PREFORMATTED_PATTERN = "(?s)\\{\\{\\{.*?\\}\\}\\}";
	
	private static final String ACTION_PATTERN = "(" +
    	PagePermission.COMMENT_ACTION + "|" +
    	PagePermission.DELETE_ACTION  + "|" +
    	PagePermission.EDIT_ACTION    + "|" +
    	PagePermission.MODIFY_ACTION  + "|" +
    	PagePermission.RENAME_ACTION  + "|" +
    	PagePermission.UPLOAD_ACTION  + "|" +
    	PagePermission.VIEW_ACTION    + ")";
	
//	private static final String ACL_PATTERN = "\\[\\{\\s*ALLOW\\s+" + "[a-zA-Z]+" + "\\s*(.*?)\\s*\\}\\]"; 
	private static final String ACL_PATTERN = "\\[\\{\\s*ALLOW\\s+" + ACTION_PATTERN + "\\s*(.*?)\\s*\\}\\]";
	
	private Pattern prePattern = Pattern.compile(PREFORMATTED_PATTERN);
	private Pattern aclPattern = Pattern.compile(ACL_PATTERN);
	
	/**
     *  Is called whenever the a new PageFilter is instantiated and
     *  reset.
     */
	@Override
	public void initialize(WikiEngine engine, Properties properties)
			throws FilterException {
		super.initialize(engine, properties);
	}

	/**
     *  This method is called before the page has been saved to the PageProvider.
     */
	@Override
	public String preSave(WikiContext wikiContext, String content) throws FilterException {
		/*
		 * if the current user has administrative permissions, i.e. the omnipotent AllPermission,
		 * in our case, WIKIADMIN, save it directly.
		 */
		if (wikiContext.hasAdminPermissions())
			return content;
		
		/*
		 * Filter out all ACLs. Non-admin users have no right to define ACLs.
		 */
		StringBuffer newContent = filterACLs(content);
		
		/*
		 * Retrieve the official ACLs from the current version.
		 */
		String currentContent = wikiContext.getEngine().getPureText(wikiContext.getPage());
		StringBuffer officialACLs = retrieveOfficialACLs(currentContent);
		
		return newContent.append(officialACLs).toString();
	}
	
	private static final int ACL_PROCESS_MODE_FILTER = 0;
	private static final int ACL_PROCESS_MODE_COLLECT = 1;
	
	private StringBuffer filterACLs(String content) {
		return processACLs(content, ACL_PROCESS_MODE_FILTER);
	}

	private StringBuffer retrieveOfficialACLs(String currentContent) {
		return processACLs(currentContent, ACL_PROCESS_MODE_COLLECT);
	}

	private StringBuffer processACLs(String content, int mode) {
		StringBuffer rv;
		if (mode == ACL_PROCESS_MODE_FILTER)
			rv = new StringBuffer(content.length());
		else // mode == ACL_PROCESS_MODE_COLLECT
			rv = new StringBuffer();
		StringBuffer sb = new StringBuffer(content);
		
		/*
		 * First, find all preformatted ranges, within which ACLs has no meaning.  
		 */
		Matcher m = prePattern.matcher(sb);
		ArrayList<Range> prelist = new ArrayList<Range>();
		while (m.find()) {
			Range range = new Range(m.start(), m.end());
			prelist.add(range);
		}
		
		/*
		 * Second, find all ACLs, considering preformatted ranges.
		 */
		m = aclPattern.matcher(sb);
		while (m.find()) {
			Range range = new Range(m.start(), m.end());
			if (Collections.binarySearch(prelist, range, new Comparator<Range>() {
				public int compare(Range r1, Range r2) {
					if (r1.start > r2.end)
						return 1;
					else if (r1.end < r2.start)
						return -1;
					else
						return 0;
				}				
			}) < 0) {
				if (mode == ACL_PROCESS_MODE_FILTER)
					m.appendReplacement(rv, "");
				else // mode == ACL_PROCESS_MODE_COLLECT
					rv.append(m.group());
			}				
		}
		if (mode == ACL_PROCESS_MODE_FILTER)
			m.appendTail(rv);
		
		return rv;
	}

	private static class Range {
		int start;
		int end;
		
		Range(int s, int e) {
			this.start = s;
			this.end = e;
		}
	}
}