<?php
/**
 * Sequence matcher for Diff
 *
 * PHP version 5
 *
 * Copyright (c) 2009 Chris Boulton <chris.boulton@interspire.com>
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  - Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *  - Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *  - Neither the name of the Chris Boulton nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * @package Diff
 * @author Chris Boulton <chris.boulton@interspire.com>
 * @copyright (c) 2009 Chris Boulton
 * @license New BSD License http://www.opensource.org/licenses/bsd-license.php
 * @version 1.1
 * @link http://github.com/chrisboulton/php-diff
 */
class Diff_SequenceMatcher {
	/**
	 *
	 * @var string|array Either a string or an array containing a callback function to determine if a line is "junk" or not.
	 */
	private $junkCallback = null;
	
	/**
	 *
	 * @var array The first sequence to compare against.
	 */
	private $a = null;
	
	/**
	 *
	 * @var array The second sequence.
	 */
	private $b = null;
	
	/**
	 *
	 * @var array Array of characters that are considered junk from the second sequence. Characters are the array key.
	 */
	private $junkDict = array ();
	
	/**
	 *
	 * @var array Array of indices that do not contain junk elements.
	 */
	private $b2j = array ();
	private $options = array ();
	private $defaultOptions = array (
			'ignoreNewLines' => false,
			'ignoreWhitespace' => false,
			'ignoreCase' => false 
	);
	
	/**
	 * The constructor.
	 * With the sequences being passed, they'll be set for the
	 * sequence matcher and it will perform a basic cleanup & calculate junk
	 * elements.
	 *
	 * @param string|array $a
	 *        	A string or array containing the lines to compare against.
	 * @param string|array $b
	 *        	A string or array containing the lines to compare.
	 * @param string|array $junkCallback
	 *        	Either an array or string that references a callback function (if there is one) to determine 'junk' characters.
	 * @param array $options        	
	 */
	public function __construct($a, $b, $junkCallback = null, $options) {
		$this->a = null;
		$this->b = null;
		$this->junkCallback = $junkCallback;
		$this->setOptions ( $options );
		$this->setSequences ( $a, $b );
	}
	
	/**
	 * Set new options
	 *
	 * @param array $options        	
	 */
	public function setOptions($options) {
		$this->options = array_merge ( $this->defaultOptions, $options );
	}
	
	/**
	 * Set the first and second sequences to use with the sequence matcher.
	 *
	 * @param string|array $a
	 *        	A string or array containing the lines to compare against.
	 * @param string|array $b
	 *        	A string or array containing the lines to compare.
	 */
	public function setSequences($a, $b) {
		$this->setSeq1 ( $a );
		$this->setSeq2 ( $b );
	}
	
	/**
	 * Set the first sequence ($a) and reset any internal caches to indicate that
	 * when calling the calculation methods, we need to recalculate them.
	 *
	 * @param string|array $a
	 *        	The sequence to set as the first sequence.
	 */
	public function setSeq1($a) {
		if (! is_array ( $a )) {
			$a = str_split ( $a );
		}
		if ($a == $this->a) {
			return;
		}
		
		$this->a = $a;
		$this->matchingBlocks = null;
		$this->opCodes = null;
	}
	
	/**
	 * Set the second sequence ($b) and reset any internal caches to indicate that
	 * when calling the calculation methods, we need to recalculate them.
	 *
	 * @param string|array $b
	 *        	The sequence to set as the second sequence.
	 */
	public function setSeq2($b) {
		if (! is_array ( $b )) {
			$b = str_split ( $b );
		}
		if ($b == $this->b) {
			return;
		}
		
		$this->b = $b;
		$this->matchingBlocks = null;
		$this->opCodes = null;
		$this->fullBCount = null;
		$this->chainB ();
	}
	
	/**
	 * Generate the internal arrays containing the list of junk and non-junk
	 * characters for the second ($b) sequence.
	 */
	private function chainB() {
		$length = count ( $this->b );
		$this->b2j = array ();
		$popularDict = array ();
		
		for($i = 0; $i < $length; ++ $i) {
			$char = $this->b [$i];
			if (isset ( $this->b2j [$char] )) {
				if ($length >= 200 && count ( $this->b2j [$char] ) * 100 > $length) {
					$popularDict [$char] = 1;
					unset ( $this->b2j [$char] );
				} else {
					$this->b2j [$char] [] = $i;
				}
			} else {
				$this->b2j [$char] = array (
						$i 
				);
			}
		}
		
		// Remove leftovers
		foreach ( array_keys ( $popularDict ) as $char ) {
			unset ( $this->b2j [$char] );
		}
		
		$this->junkDict = array ();
		if (is_callable ( $this->junkCallback )) {
			foreach ( array_keys ( $popularDict ) as $char ) {
				if (call_user_func ( $this->junkCallback, $char )) {
					$this->junkDict [$char] = 1;
					unset ( $popularDict [$char] );
				}
			}
			
			foreach ( array_keys ( $this->b2j ) as $char ) {
				if (call_user_func ( $this->junkCallback, $char )) {
					$this->junkDict [$char] = 1;
					unset ( $this->b2j [$char] );
				}
			}
		}
	}
	
	/**
	 * Checks if a particular character is in the junk dictionary
	 * for the list of junk characters.
	 * 
	 * @param
	 *        	$b
	 * @return boolean True if the character is considered junk. False if not.
	 */
	private function isBJunk($b) {
		if (isset ( $this->juncDict [$b] )) {
			return true;
		}
		
		return false;
	}
	
	/**
	 * Find the longest matching block in the two sequences, as defined by the
	 * lower and upper constraints for each sequence.
	 * (for the first sequence,
	 * $alo - $ahi and for the second sequence, $blo - $bhi)
	 *
	 * Essentially, of all of the maximal matching blocks, return the one that
	 * startest earliest in $a, and all of those maximal matching blocks that
	 * start earliest in $a, return the one that starts earliest in $b.
	 *
	 * If the junk callback is defined, do the above but with the restriction
	 * that the junk element appears in the block. Extend it as far as possible
	 * by matching only junk elements in both $a and $b.
	 *
	 * @param int $alo
	 *        	The lower constraint for the first sequence.
	 * @param int $ahi
	 *        	The upper constraint for the first sequence.
	 * @param int $blo
	 *        	The lower constraint for the second sequence.
	 * @param int $bhi
	 *        	The upper constraint for the second sequence.
	 * @return array Array containing the longest match that includes the starting position in $a, start in $b and the length/size.
	 */
	public function findLongestMatch($alo, $ahi, $blo, $bhi) {
		$a = $this->a;
		$b = $this->b;
		
		$bestI = $alo;
		$bestJ = $blo;
		$bestSize = 0;
		
		$j2Len = array ();
		$nothing = array ();
		
		for($i = $alo; $i < $ahi; ++ $i) {
			$newJ2Len = array ();
			$jDict = $this->arrayGetDefault ( $this->b2j, $a [$i], $nothing );
			foreach ( $jDict as $jKey => $j ) {
				if ($j < $blo) {
					continue;
				} else if ($j >= $bhi) {
					break;
				}
				
				$k = $this->arrayGetDefault ( $j2Len, $j - 1, 0 ) + 1;
				$newJ2Len [$j] = $k;
				if ($k > $bestSize) {
					$bestI = $i - $k + 1;
					$bestJ = $j - $k + 1;
					$bestSize = $k;
				}
			}
			
			$j2Len = $newJ2Len;
		}
		
		while ( $bestI > $alo && $bestJ > $blo && ! $this->isBJunk ( $b [$bestJ - 1] ) && ! $this->linesAreDifferent ( $bestI - 1, $bestJ - 1 ) ) {
			-- $bestI;
			-- $bestJ;
			++ $bestSize;
		}
		
		while ( $bestI + $bestSize < $ahi && ($bestJ + $bestSize) < $bhi && ! $this->isBJunk ( $b [$bestJ + $bestSize] ) && ! $this->linesAreDifferent ( $bestI + $bestSize, $bestJ + $bestSize ) ) {
			++ $bestSize;
		}
		
		while ( $bestI > $alo && $bestJ > $blo && $this->isBJunk ( $b [$bestJ - 1] ) && ! $this->isLineDifferent ( $bestI - 1, $bestJ - 1 ) ) {
			-- $bestI;
			-- $bestJ;
			++ $bestSize;
		}
		
		while ( $bestI + $bestSize < $ahi && $bestJ + $bestSize < $bhi && $this->isBJunk ( $b [$bestJ + $bestSize] ) && ! $this->linesAreDifferent ( $bestI + $bestSize, $bestJ + $bestSize ) ) {
			++ $bestSize;
		}
		
		return array (
				$bestI,
				$bestJ,
				$bestSize 
		);
	}
	
	/**
	 * Check if the two lines at the given indexes are different or not.
	 *
	 * @param int $aIndex
	 *        	Line number to check against in a.
	 * @param int $bIndex
	 *        	Line number to check against in b.
	 * @return boolean True if the lines are different and false if not.
	 */
	public function linesAreDifferent($aIndex, $bIndex) {
		$lineA = $this->a [$aIndex];
		$lineB = $this->b [$bIndex];
		
		if ($this->options ['ignoreWhitespace']) {
			$replace = array (
					"\t",
					' ' 
			);
			$lineA = str_replace ( $replace, '', $lineA );
			$lineB = str_replace ( $replace, '', $lineB );
		}
		
		if ($this->options ['ignoreCase']) {
			$lineA = strtolower ( $lineA );
			$lineB = strtolower ( $lineB );
		}
		
		if ($lineA != $lineB) {
			return true;
		}
		
		return false;
	}
	
	/**
	 * Return a nested set of arrays for all of the matching sub-sequences
	 * in the strings $a and $b.
	 *
	 * Each block contains the lower constraint of the block in $a, the lower
	 * constraint of the block in $b and finally the number of lines that the
	 * block continues for.
	 *
	 * @return array Nested array of the matching blocks, as described by the function.
	 */
	public function getMatchingBlocks() {
		if (! empty ( $this->matchingBlocks )) {
			return $this->matchingBlocks;
		}
		
		$aLength = count ( $this->a );
		$bLength = count ( $this->b );
		
		$queue = array (
				array (
						0,
						$aLength,
						0,
						$bLength 
				) 
		);
		
		$matchingBlocks = array ();
		while ( ! empty ( $queue ) ) {
			list ( $alo, $ahi, $blo, $bhi ) = array_pop ( $queue );
			$x = $this->findLongestMatch ( $alo, $ahi, $blo, $bhi );
			list ( $i, $j, $k ) = $x;
			if ($k) {
				$matchingBlocks [] = $x;
				if ($alo < $i && $blo < $j) {
					$queue [] = array (
							$alo,
							$i,
							$blo,
							$j 
					);
				}
				
				if ($i + $k < $ahi && $j + $k < $bhi) {
					$queue [] = array (
							$i + $k,
							$ahi,
							$j + $k,
							$bhi 
					);
				}
			}
		}
		
		usort ( $matchingBlocks, array (
				$this,
				'tupleSort' 
		) );
		
		$i1 = 0;
		$j1 = 0;
		$k1 = 0;
		$nonAdjacent = array ();
		foreach ( $matchingBlocks as $block ) {
			list ( $i2, $j2, $k2 ) = $block;
			if ($i1 + $k1 == $i2 && $j1 + $k1 == $j2) {
				$k1 += $k2;
			} else {
				if ($k1) {
					$nonAdjacent [] = array (
							$i1,
							$j1,
							$k1 
					);
				}
				
				$i1 = $i2;
				$j1 = $j2;
				$k1 = $k2;
			}
		}
		
		if ($k1) {
			$nonAdjacent [] = array (
					$i1,
					$j1,
					$k1 
			);
		}
		
		$nonAdjacent [] = array (
				$aLength,
				$bLength,
				0 
		);
		
		$this->matchingBlocks = $nonAdjacent;
		return $this->matchingBlocks;
	}
	
	/**
	 * Return a list of all of the opcodes for the differences between the
	 * two strings.
	 *
	 * The nested array returned contains an array describing the opcode
	 * which includes:
	 * 0 - The type of tag (as described below) for the opcode.
	 * 1 - The beginning line in the first sequence.
	 * 2 - The end line in the first sequence.
	 * 3 - The beginning line in the second sequence.
	 * 4 - The end line in the second sequence.
	 *
	 * The different types of tags include:
	 * replace - The string from $i1 to $i2 in $a should be replaced by
	 * the string in $b from $j1 to $j2.
	 * delete - The string in $a from $i1 to $j2 should be deleted.
	 * insert - The string in $b from $j1 to $j2 should be inserted at
	 * $i1 in $a.
	 * equal - The two strings with the specified ranges are equal.
	 *
	 * @return array Array of the opcodes describing the differences between the strings.
	 */
	public function getOpCodes() {
		if (! empty ( $this->opCodes )) {
			return $this->opCodes;
		}
		
		$i = 0;
		$j = 0;
		$this->opCodes = array ();
		
		$blocks = $this->getMatchingBlocks ();
		foreach ( $blocks as $block ) {
			list ( $ai, $bj, $size ) = $block;
			$tag = '';
			if ($i < $ai && $j < $bj) {
				$tag = 'replace';
			} else if ($i < $ai) {
				$tag = 'delete';
			} else if ($j < $bj) {
				$tag = 'insert';
			}
			
			if ($tag) {
				$this->opCodes [] = array (
						$tag,
						$i,
						$ai,
						$j,
						$bj 
				);
			}
			
			$i = $ai + $size;
			$j = $bj + $size;
			
			if ($size) {
				$this->opCodes [] = array (
						'equal',
						$ai,
						$i,
						$bj,
						$j 
				);
			}
		}
		return $this->opCodes;
	}
	
	/**
	 * Return a series of nested arrays containing different groups of generated
	 * opcodes for the differences between the strings with up to $context lines
	 * of surrounding content.
	 *
	 * Essentially what happens here is any big equal blocks of strings are stripped
	 * out, the smaller subsets of changes are then arranged in to their groups.
	 * This means that the sequence matcher and diffs do not need to include the full
	 * content of the different files but can still provide context as to where the
	 * changes are.
	 *
	 * @param int $context
	 *        	The number of lines of context to provide around the groups.
	 * @return array Nested array of all of the grouped opcodes.
	 */
	public function getGroupedOpcodes($context = 3) {
		$opCodes = $this->getOpCodes ();
		if (empty ( $opCodes )) {
			$opCodes = array (
					array (
							'equal',
							0,
							1,
							0,
							1 
					) 
			);
		}
		
		if ($opCodes [0] [0] == 'equal') {
			$opCodes [0] = array (
					$opCodes [0] [0],
					max ( $opCodes [0] [1], $opCodes [0] [2] - $context ),
					$opCodes [0] [2],
					max ( $opCodes [0] [3], $opCodes [0] [4] - $context ),
					$opCodes [0] [4] 
			);
		}
		
		$lastItem = count ( $opCodes ) - 1;
		if ($opCodes [$lastItem] [0] == 'equal') {
			list ( $tag, $i1, $i2, $j1, $j2 ) = $opCodes [$lastItem];
			$opCodes [$lastItem] = array (
					$tag,
					$i1,
					min ( $i2, $i1 + $context ),
					$j1,
					min ( $j2, $j1 + $context ) 
			);
		}
		
		$maxRange = $context * 2;
		$groups = array ();
		$group = array ();
		foreach ( $opCodes as $code ) {
			list ( $tag, $i1, $i2, $j1, $j2 ) = $code;
			if ($tag == 'equal' && $i2 - $i1 > $maxRange) {
				$group [] = array (
						$tag,
						$i1,
						min ( $i2, $i1 + $context ),
						$j1,
						min ( $j2, $j1 + $context ) 
				);
				$groups [] = $group;
				$group = array ();
				$i1 = max ( $i1, $i2 - $context );
				$j1 = max ( $j1, $j2 - $context );
			}
			$group [] = array (
					$tag,
					$i1,
					$i2,
					$j1,
					$j2 
			);
		}
		
		if (! empty ( $group ) && ! (count ( $group ) == 1 && $group [0] [0] == 'equal')) {
			$groups [] = $group;
		}
		
		return $groups;
	}
	
	/**
	 * Return a measure of the similarity between the two sequences.
	 * This will be a float value between 0 and 1.
	 *
	 * Out of all of the ratio calculation functions, this is the most
	 * expensive to call if getMatchingBlocks or getOpCodes is yet to be
	 * called. The other calculation methods (quickRatio and realquickRatio)
	 * can be used to perform quicker calculations but may be less accurate.
	 *
	 * The ratio is calculated as (2 * number of matches) / total number of
	 * elements in both sequences.
	 *
	 * @return float The calculated ratio.
	 */
	public function Ratio() {
		$matches = array_reduce ( $this->getMatchingBlocks (), array (
				$this,
				'ratioReduce' 
		), 0 );
		return $this->calculateRatio ( $matches, count ( $this->a ) + count ( $this->b ) );
	}
	
	/**
	 * Helper function to calculate the number of matches for Ratio().
	 *
	 * @param int $sum
	 *        	The running total for the number of matches.
	 * @param array $triple
	 *        	Array containing the matching block triple to add to the running total.
	 * @return int The new running total for the number of matches.
	 */
	private function ratioReduce($sum, $triple) {
		return $sum + ($triple [count ( $triple ) - 1]);
	}
	
	/**
	 * Quickly return an upper bound ratio for the similarity of the strings.
	 * This is quicker to compute than Ratio().
	 *
	 * @return float The calculated ratio.
	 */
	private function quickRatio() {
		if ($this->fullBCount === null) {
			$this->fullBCount = array ();
			$bLength = count ( $this->b );
			for($i = 0; $i < $bLength; ++ $i) {
				$char = $this->b [$i];
				$this->fullBCount [$char] = $this->arrayGetDefault ( $this->fullBCount, $char, 0 ) + 1;
			}
		}
		
		$avail = array ();
		$matches = 0;
		$aLength = count ( $this->a );
		for($i = 0; $i < $aLength; ++ $i) {
			$char = $this->a [$i];
			if (isset ( $avail [$char] )) {
				$numb = $avail [$char];
			} else {
				$numb = $this->arrayGetDefault ( $this->fullBCount, $char, 0 );
			}
			$avail [$char] = $numb - 1;
			if ($numb > 0) {
				++ $matches;
			}
		}
		
		$this->calculateRatio ( $matches, count ( $this->a ) + count ( $this->b ) );
	}
	
	/**
	 * Return an upper bound ratio really quickly for the similarity of the strings.
	 * This is quicker to compute than Ratio() and quickRatio().
	 *
	 * @return float The calculated ratio.
	 */
	private function realquickRatio() {
		$aLength = count ( $this->a );
		$bLength = count ( $this->b );
		
		return $this->calculateRatio ( min ( $aLength, $bLength ), $aLength + $bLength );
	}
	
	/**
	 * Helper function for calculating the ratio to measure similarity for the strings.
	 * The ratio is defined as being 2 * (number of matches / total length)
	 *
	 * @param int $matches
	 *        	The number of matches in the two strings.
	 * @param int $length
	 *        	The length of the two strings.
	 * @return float The calculated ratio.
	 */
	private function calculateRatio($matches, $length = 0) {
		if ($length) {
			return 2 * ($matches / $length);
		} else {
			return 1;
		}
	}
	
	/**
	 * Helper function that provides the ability to return the value for a key
	 * in an array of it exists, or if it doesn't then return a default value.
	 * Essentially cleaner than doing a series of if(isset()) {} else {} calls.
	 *
	 * @param array $array
	 *        	The array to search.
	 * @param string $key
	 *        	The key to check that exists.
	 * @param mixed $default
	 *        	The value to return as the default value if the key doesn't exist.
	 * @return mixed The value from the array if the key exists or otherwise the default.
	 */
	private function arrayGetDefault($array, $key, $default) {
		if (isset ( $array [$key] )) {
			return $array [$key];
		} else {
			return $default;
		}
	}
	
	/**
	 * Sort an array by the nested arrays it contains.
	 * Helper function for getMatchingBlocks
	 *
	 * @param array $a
	 *        	First array to compare.
	 * @param array $b
	 *        	Second array to compare.
	 * @return int -1, 0 or 1, as expected by the usort function.
	 */
	private function tupleSort($a, $b) {
		$max = max ( count ( $a ), count ( $b ) );
		for($i = 0; $i < $max; ++ $i) {
			if ($a [$i] < $b [$i]) {
				return - 1;
			} else if ($a [$i] > $b [$i]) {
				return 1;
			}
		}
		
		if (count ( $a ) == count ( $b )) {
			return 0;
		} else if (count ( $a ) < count ( $b )) {
			return - 1;
		} else {
			return 1;
		}
	}
}