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//
//  ========================================================================
//  Copyright (c) 1995-2018 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.util;

import java.nio.charset.StandardCharsets;
import java.util.Arrays;


/**
 * SearchPattern
 *
 * Fast search for patterns within strings and arrays of bytes.
 * Uses an implementation of the Boyer–Moore–Horspool algorithm
 * with a 256 character alphabet.
 * 
 * The algorithm has an average-case complexity of O(n) 
 * on random text and O(nm) in the worst case.
 * where: 
 *    m = pattern length
 *    n = length of data to search
 */
public class SearchPattern
{
    static final int alphabetSize = 256;
    private int[] table;
    private byte[] pattern;    
    
    /**
     * Produces a SearchPattern instance which can be used
     * to find matches of the pattern in data
     * @param pattern byte array containing the pattern
     * @return a new SearchPattern instance using the given pattern
     */
    public static SearchPattern compile(byte[] pattern)
    {
        return new SearchPattern(Arrays.copyOf(pattern, pattern.length));
    }
    
    /**
     * Produces a SearchPattern instance which can be used
     * to find matches of the pattern in data
     * @param pattern string containing the pattern
     * @return a new SearchPattern instance using the given pattern
     */
    public static SearchPattern compile(String pattern)
    {
        return new SearchPattern(pattern.getBytes(StandardCharsets.UTF_8));
    }
    
    /**
     * @param pattern byte array containing the pattern used for matching
     */
    private SearchPattern(byte[] pattern)
    {
        this.pattern = pattern;
        
        if(pattern.length == 0) 
            throw new IllegalArgumentException("Empty Pattern");
        
        //Build up the pre-processed table for this pattern.
        table = new int[alphabetSize];
        for(int i = 0; i data.length)
            throw new IllegalArgumentException("(offset+length) out of bounds of data[]");
    }

    /**
     * @return The length of the pattern in bytes.
     */
    public int getLength()
    {
        return pattern.length;
    }
}