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<?php
/**
* Standard diff function plus some extras for handling XHTML diffs.
* @copyright © 2007 The Open University
* @author s.marshall@open.ac.uk
* @license http://www.gnu.org/copyleft/gpl.html GNU Public License
* @package ouwiki
*//** */
// Standard diff
////////////////
/**
* Basic diff utility function, using standard diff algorithm.
*
* Based on Bell Laboratories Computing Science Technical Report #41,
* July 1976, Hunt & McIlroy, Appendix A.1 and A.3.
*
* http://www.cs.dartmouth.edu/~doug/diff.ps
*
* @param array $file1 Array of lines in file 1. The first line in the file
* MUST BE INDEX 1 NOT ZERO!!
* @param array $file2 Array of lines in file 2, again starting from 1.
* @return array An array with one entry (again 1-based) for each line in
* file 1, with its corresponding position in file 2 or 0 if it isn't there.
*/
function ouwiki_diff_internal($file1,$file2) {
// Basic variables
$n=count($file2);
$m=count($file1);
// Special-case for empty file2 which otherwise causes error
if($n==0)
{
$result=array();
for($i=1;$i<=$m;$i++)
{
$result[$i]=0;
}
return $result;
}
// Step 1 Build list of elements
/////////
$V=array();
for($j=1;$j<=$n;$j++) {
$V[$j]=new StdClass;
$V[$j]->serial=$j;
$V[$j]->hash=crc32($file2[$j]);
}
// Step 2 Sort by hash,serial
/////////
usort($V,"ouwiki_diff_sort_v");
// Make it start from 1 again
array_unshift($V,'bogus');
unset($V[0]);
// $V is now an array including the line number 'serial' and hash
// of each line in file 2, sorted by hash and then serial.
// Step 3 Equivalence classes
/////////
$E=array();
$E[0]=new StdClass;
$E[0]->serial=0;
$E[0]->last=true;
for($j=1;$j<=$n;$j++) {
$E[$j]=new StdClass;
$E[$j]->serial=$V[$j]->serial;
$E[$j]->last=$j===$n || $V[$j]->hash!==$V[$j+1]->hash;
}
// E is now an array sorted the same way as $V which includes
// the line number 'serial' and whether or not that is the 'last'
// line in the given equivalence class, i.e. set of identical lines
// Step 4 For each line in file1, finds start of equivalence class
/////////
$P=array();
for($i=1;$i<=$m;$i++) {
// Find matching last entry from equivalence list
$P[$i]=ouwiki_diff_find_last($V,$E,crc32($file1[$i]));
}
// P is now an array that finds the index (within $V) of the *first*
// matching line in $V (referencing file 2, but not a line number,
// because sorted in $V order) for each line in file 1. In other words
// if you were to start at the P-value in $V and continue through, you
// would find all the lines from file 2 that are equal to the given line
// from file 1.
// Step 5 Initialise vector of candidates
/////////
// I do not trust PHP references further than I can throw them (preferably
// at the idiot who came up with the idea) so I am using a separate array
// to store candidates and all references are integers into that.
$candidates=array();
$candidates[0]=new StdClass;
$candidates[0]->a=0;
$candidates[0]->b=0;
$candidates[0]->previous=null;
$candidates[1]=new StdClass;
$candidates[1]->a=$m+1;
$candidates[1]->b=$n+1;
$candidates[1]->previous=null;
$K=array();
$K[0]=0; // Ref to candidate 0
$K[1]=1; // Ref to candidate 1
$k=0;
// Step 6 Merge stage
/////////
for($i=1;$i<=$m;$i++) {
if($P[$i]!==0) {
ouwiki_diff_merge($K,$k,$i,$E,$P[$i],$candidates);
}
}
// Step 7
/////////
$J=array();
for($i=1;$i<=$m;$i++) {
$J[$i]=0;
}
// Step 8 Follow candidate chain to make nice representation
/////////
$index=$K[$k];
while(!is_null($index)) {
// Stop when we reach the first, dummy candidate
if($candidates[$index]->a!=0) {
$J[$candidates[$index]->a]=$candidates[$index]->b;
}
$index=$candidates[$index]->previous;
}
// Step 9 Get rid of 'jackpots' (hash collisions)
/////////
for($i=1;$i<=$m;$i++) {
if($J[$i]!=0 && $file1[$i]!=$file2[$J[$i]]) {
$J[$i]=0;
}
}
// Done! (Maybe.)
return $J;
}
// Functions needed by parts of the algorithm
/////////////////////////////////////////////
// Merge, from step 7 (Appendix A.3)
function ouwiki_diff_merge(&$K,&$k,$i,&$E,$p,&$candidates) {
$r=0;
$c=$K[0];
while(true) {
$j=$E[$p]->serial; // Paper says 'i' but this is wrong (OCR)
// Binary search in $K from $r to $k
$min=$r;
$max=$k+1;
while(true) {
$try = (int)(($min+$max)/2);
if($candidates[$K[$try]]->b >= $j) {
$max=$try;
} else if($candidates[$K[$try+1]]->b <= $j) {
$min=$try+1;
} else { // $try is less and $try+1 is more
$s=$try;
break;
}
if($max<=$min) {
$s=-1;
break;
}
}
if($s>-1) {
if($candidates[$K[$s+1]]->b > $j) {
// Create new candidate
$index=count($candidates);
$candidates[$index]=new StdClass;
$candidates[$index]->a=$i;
$candidates[$index]->b=$j;
$candidates[$index]->previous=$K[$s];
$K[$r]=$c;
$r=$s+1;
$c=$index; // Or should this go before?
}
if($s===$k) {
$K[$k+2]=$K[$k+1];
$k++;
break;
}
}
if($E[$p]->last) {
break;
}
$p++;
}
$K[$r]=$c;
}
// From Step 2
function ouwiki_diff_sort_v($a,$b) {
if($a->hash < $b->hash) {
return -1;
} else if($a->hash > $b->hash) {
return 1;
} else if($a->serial < $b->serial) {
return -1;
} else if($a->serial > $b->serial) {
return 1;
} else {
return 0;
}
}
// From Step 4
function ouwiki_diff_find_last(&$V,&$E,$hash) {
// Binary search in $V until we find something with $hash
// Min = 1, array is 1-indexed
$min=1;
// Max = 1 higher than highest key
end($V);
$max=key($V)+1;
while(true) {
$try = (int)(($min+$max)/2);
if($V[$try]->hash > $hash) {
$max=$try;
} else if($V[$try]->hash < $hash) {
$min=$try+1;
} else { // Equal
break;
}
if($max<=$min) {
// No matching line
return 0;
}
}
// Now check back in $E to find the first line of that equivalence class
for($j=$try;!$E[$j-1]->last;$j--) ;
return $j;
}
///////////////////////////
/**
* Class representing one 'line' of HTML content for the purpose of
* text comparison.
*/
class ouwiki_line {
/** Array of ouwiki_words */
var $words=array();
/**
* Construct line object based on a chunk of text.
* @param string $data Text data that makes up this 'line'. (May include line breaks etc.)
* @param int $linepos Position number for first character in text
*/
public function __construct($data,$linepos) {
// 1. Turn things we don't want into spaces (so that positioning stays same)
// Whitespace replaced with space
$data=preg_replace('/\s/',' ',$data);
// Various ways of writing non-breaking space replaced with space
// Note that using a single param for replace only works because all
// the search strings are 6 characters long
$data=str_replace(array(' ',' ',' '),' ',$data);
// Tags replaced with equal number of spaces
$data = preg_replace_callback('/<.*?'.'>/', function($matches) {
return preg_replace("/./", " ", $matches[0]);
}, $data);
// 2. Analyse string so that each space-separated thing
// is counted as a 'word' (note these may not be real words,
// for instance words may include punctuation at either end)
$pos=0;
while(true) {
// Find a non-space
$strlendata = strlen($data);
for(;$pos < $strlendata && substr($data,$pos,1)===' ';$pos++) ;
if($pos==$strlendata) {
// No more content
break;
}
// Aaaand find the next space after that
$space2=strpos($data,' ',$pos);
if($space2===false) {
// No more spaces? Everything left must be a word
$this->words[]=new ouwiki_word(substr($data,$pos),$pos+$linepos);
break;
} else {
$this->words[]=new ouwiki_word(substr($data,$pos,$space2-$pos),$pos+$linepos);
$pos=$space2;
}
}
}
/**
* Old syntax of class constructor. Deprecated in PHP7.
*
* @deprecated since Moodle 3.1
*/
public function ouwiki_line($data, $linepos) {
debugging('Use of class name as constructor is deprecated', DEBUG_DEVELOPER);
self::__construct($data, $linepos);
}
/**
* @return string Normalised string representation of this line object
*/
function get_as_string() {
$result='';
foreach($this->words as $word) {
if($result!=='') {
$result.=' ';
}
$result.=$word->word;
}
return $result;
}
/**
* Static function converts lines to strings.
* @param array $lines Array of ouwiki_line
* @return array Array of strings
*/
static function get_as_strings($lines) {
$strings=array();
foreach($lines as $key=>$value) {
$strings[$key]=$value->get_as_string();
}
return $strings;
}
/**
* @return True if there are no words in the line
*/
function is_empty() {
return count($this->words)===0;
}
}
/**
* Represents single word for html comparison. Note that words
* are just chunks of plain text and may not be actual words;
* they could include punctuation or (if there was e.g. a span
* in the middle of something) even be part-words.
*/
class ouwiki_word {
/** Word as plain string */
var $word;
/** Start position in original xhtml */
var $start;
public function __construct($word,$start) {
$this->word=$word;
$this->start=$start;
}
/**
* Old syntax of class constructor. Deprecated in PHP7.
*
* @deprecated since Moodle 3.1
*/
public function ouwiki_word($word, $start) {
debugging('Use of class name as constructor is deprecated', DEBUG_DEVELOPER);
self::__construct($word, $start);
}
}
/**
* Prepares XHTML content for text difference comparison.
* @param string $content XHTML content [NO SLASHES]
* @return array Array of ouwiki_line objects
*/
function ouwiki_diff_html_to_lines($content) {
// These functions are a pain mostly because PHP preg_* don't provide
// proper information as to the start/end position of matches. As a
// consequence there is a lot of hackery going down. At every point we
// replace things with spaces rather than getting rid, in order to store
// positions within original content.
// Get rid of all script, style, object tags (that might contain non-text
// outside tags)
$content=preg_replace_callback(
'^(<script .*?</script>)|(<object .*?</object>)|(<style .*?</style>)^i', function($matches) {
return preg_replace("/./", " ", $matches[0]);
}, $content);
// Get rid of all ` symbols as we are going to use these for a marker later.
$content=preg_replace('/[`]/',' ',$content);
// Put line breaks on block tags. Mark each line break with ` symbol
$blocktags=array('p','div','h1','h2','h3','h4','h5','h6','td','li');
$taglist='';
foreach($blocktags as $blocktag) {
if($taglist!=='') {
$taglist.='|';
}
$taglist.="<$blocktag>|<\\/$blocktag>";
}
$content = preg_replace_callback('/((' . $taglist . ')\s*)+/i', function($matches) {
return "`" . preg_replace("/./", " ", substr($matches[0], 1));
}, $content);
// Now go through splitting each line
$lines=array(); $index=1;
$pos=0;
while($pos<strlen($content)) {
$nextline=strpos($content,'`',$pos);
if($nextline===false) {
// No more line breaks? Take content to end
$nextline=strlen($content);
}
$linestr=substr($content,$pos,$nextline-$pos);
$line=new ouwiki_line($linestr,$pos);
if(!$line->is_empty()) {
$lines[$index++]=$line;
}
$pos=$nextline+1;
}
return $lines;
}
/**
* Represents a changed area of file and where it is located in the
* two source files.
*/
class ouwiki_change_range {
var $file1start,$file1count;
var $file2start,$file2count;
}
/**
* A more logical representation of the results from ouwiki_internal_diff()
*/
class ouwiki_changes {
/** Array of indexes (in file 2) of added lines */
var $adds;
/** Array of indexes (in file 1) of deleted lines */
var $deletes;
/** Array of changed ranges */
var $changes;
/**
* @param array $diff Array from line indices in file1
* to indices in file2. All indices 1-based.
* @param int $count2 Number of lines in file2
*/
public function __construct($diff,$count2) {
// Find deleted lines
$this->deletes=self::internal_find_deletes($diff,$count2);
// Added lines work the same way after the comparison is
// reversed.
$this->adds=self::internal_find_deletes(
ouwiki_diff_internal_flip($diff,$count2),count($diff));
// Changed ranges are all the other lines from file 1 that
// weren't found in file 2 but aren't deleted, and the
// corresponding lines from file 2 (between the equivalent
// 'found' lines).
$this->changes=array();
$matchbefore=0;
$inrange=-1; $lastrange=-1;
foreach($diff as $index1=>$index2) {
// Changed line if this isn't in 'deleted' section and
// doesn't have a match in file2.
if($index2===0 && !in_array($index1,$this->deletes)) {
if($inrange===-1) {
// Not already in a range, start a new one at array end
$inrange=count($this->changes);
$this->changes[$inrange]=new ouwiki_change_range;
$this->changes[$inrange]->file1start=$index1;
$this->changes[$inrange]->file1count=1;
$this->changes[$inrange]->file2start=$matchbefore+1; // Last valid from file2
$this->changes[$inrange]->file2count=0;
$lastrange=$inrange;
} else {
// One more line that gets added to the range
$this->changes[$inrange]->file1count++;
}
} else {
// Not in a range any more
$inrange=-1;
// If we have a line match...
if($index2!==0) {
// Remember this line as next range must start after it
$matchbefore=$index2;
// If last range is still looking for a number, fill that in too
if($lastrange!==-1) {
$this->changes[$lastrange]->file2count=$index2
-$this->changes[$lastrange]->file2start;
$lastrange=-1;
}
}
}
}
// Unfinished range in file2 gets end of file
if($lastrange!==-1) {
$this->changes[$lastrange]->file2count=$count2
-$this->changes[$lastrange]->file2start+1;
}
}
/**
* Old syntax of class constructor. Deprecated in PHP7.
*
* @deprecated since Moodle 3.1
*/
public function ouwiki_changes($diff, $count2) {
debugging('Use of class name as constructor is deprecated', DEBUG_DEVELOPER);
self::__construct($diff, $count2);
}
/**
* Find deleted lines. These are lines in file1 that
* cannot be present even in modified form in file2
* because we have matching lines around them.
* O(n) algorithm.
* @param array $diff Array of file1->file2 indexes
* @param int $count2 Count of lines in file2
*/
function internal_find_deletes($diff,$count2) {
$deletes=array();
// 1. Create a new array that includes the lowest-valued
// index2 value below each run of 0s.
// I.e. if our array is say 1,2,0,0,0,3,0 then the
// resulting array will be -,-,3,3,3,-,0
$squidges=array();
$lowest=0;
$countdiff = count($diff);
for($index1=$countdiff;$index1>=1;$index1--) {
$index2=$diff[$index1];
if($index2===0) {
$squidges[$index1]=$lowest;
} else {
$lowest=$index2;
}
}
// 2. OK now we can use this new array to work out
// items that are known to be deleted because we
// have matching items either side
$highest=0;
foreach($diff as $index1=>$index2) {
if($index2===0) {
if($highest===$count2 || $highest+1===$squidges[$index1]) {
// Yep! Definitely deleted.
$deletes[]=$index1;
}
} else {
$highest=$index2;
}
}
return $deletes;
}
}
/**
* Flips around the array returned by ouwiki_diff_internal
* so that it refers to lines from the other file.
* @param array $diff Array of index1=>index2
* @param int $count2 Count of lines in file 2
* @return array Flipped version
*/
function ouwiki_diff_internal_flip($diff,$count2) {
$flip=array();
for($i=1;$i<=$count2;$i++) {
$flip[$i]=0;
}
foreach($diff as $index1=>$index2) {
if($index2!==0) {
$flip[$index2]=$index1;
}
}
return $flip;
}
/**
* Compares two files based initially on lines and then on words within the lines that
* differ.
* @param array $lines1 Array of ouwiki_line
* @param array $lines2 Array of ouwiki_line
* @return array (deleted,added); deleted and added are arrays of ouwiki_word with
* position numbers from $lines1 and $lines2 respectively
*/
function ouwiki_diff_words($lines1,$lines2) {
// Prepare arrays
$deleted=array();
$added=array();
// Get line difference
$linediff=ouwiki_diff(
ouwiki_line::get_as_strings($lines1),
ouwiki_line::get_as_strings($lines2));
// Handle lines that were entirely deleted
foreach($linediff->deletes as $deletedline) {
$deleted = array_merge($deleted, $lines1[$deletedline]->words);
}
// And ones that were entirely added
foreach($linediff->adds as $addedline) {
$added = array_merge($added, $lines2[$addedline]->words);
}
// Changes get diffed at the individual-word level
foreach($linediff->changes as $changerange) {
// Build list of all words in each side of the range
$file1words=array();
for($index=$changerange->file1start;
$index<$changerange->file1start+$changerange->file1count;$index++) {
foreach($lines1[$index]->words as $word) {
$file1words[]=$word;
}
}
$file2words=array();
for($index=$changerange->file2start;
$index<$changerange->file2start+$changerange->file2count;$index++) {
foreach($lines2[$index]->words as $word) {
$file2words[]=$word;
}
}
// Make arrays 1-based
array_unshift($file1words,'dummy');
unset($file1words[0]);
array_unshift($file2words,'dummy');
unset($file2words[0]);
// Convert word lists into plain strings
$file1strings=array();
foreach($file1words as $index=>$word) {
$file1strings[$index]=$word->word;
}
$file2strings=array();
foreach($file2words as $index=>$word) {
$file2strings[$index]=$word->word;
}
// Run diff on strings
$worddiff=ouwiki_diff($file1strings,$file2strings);
foreach($worddiff->adds as $index) {
$added[]=$file2words[$index];
}
foreach($worddiff->deletes as $index) {
$deleted[]=$file1words[$index];
}
foreach($worddiff->changes as $changerange) {
for($index=$changerange->file1start;
$index<$changerange->file1start+$changerange->file1count;$index++) {
$deleted[]=$file1words[$index];
}
for($index=$changerange->file2start;
$index<$changerange->file2start+$changerange->file2count;$index++) {
$added[]=$file2words[$index];
}
}
}
return array($deleted,$added);
}
/**
* Runs diff and interprets results into ouwiki_changes object.
* @param array $file1 Array of lines in file 1. The first line in the file
* MUST BE INDEX 1 NOT ZERO!!
* @param array $file2 Array of lines in file 2, again starting from 1.
* @return ouwiki_changes Object describing changes
*/
function ouwiki_diff($file1,$file2) {
return new ouwiki_changes(ouwiki_diff_internal($file1,$file2),count($file2));
}
/**
* Adds HTML span elements to $html around the words listed in $words.
* @param string $html HTML content
* @param array $words Array of ouwiki_word to mark
* @param string $markerclass Name of class for span element
* @return HTML with markup added
*/
function ouwiki_diff_add_markers($html,$words,$markerclass,$beforetext,$aftertext) {
// Sort words by start position
usort($words, function($a, $b) {
return $a->start - $b->start;
});
// Add marker for each word. We use an odd tag name which will
// be replaced by span later, this for ease of replacing
$spanstart="<ouwiki_diff_add_markers>";
$pos=0;
$result='';
foreach($words as $word) {
// Add everything up to the word
$result.=substr($html,$pos,$word->start-$pos);
// Add word
$result.=$spanstart.$word->word.'</ouwiki_diff_add_markers>';
// Update position
$pos=$word->start+strlen($word->word);
}
// Add everything after last word
$result.=substr($html,$pos);
// If we end a marker then immediately start one, get rid of
// both the end and start
$result=preg_replace('^</ouwiki_diff_add_markers>(\s*)<ouwiki_diff_add_markers>^','$1',$result);
// Turn markers into proper span
$result=preg_replace('^<ouwiki_diff_add_markers>^',$beforetext.'<span class="'.$markerclass.'">',$result);
$result=preg_replace('^</ouwiki_diff_add_markers>^','</span>'.$aftertext,$result);
return $result;
}
/**
* Compares two HTML files. (This is the main function that everything else supports.)
* @param string $html1 XHTML for file 1
* @param string $html2 XHTML for file 2
* @return array ($result1,$result2) to be displayed indicating the differences
*/
function ouwiki_diff_html($html1,$html2) {
$lines1=ouwiki_diff_html_to_lines($html1);
$lines2=ouwiki_diff_html_to_lines($html2);
list($deleted,$added)=ouwiki_diff_words($lines1,$lines2);
$result1=ouwiki_diff_add_markers($html1,$deleted,'ouw_deleted',
'<strong class="accesshide">'.get_string('deletedbegins','wiki').'</strong>',
'<strong class="accesshide">'.get_string('deletedends','wiki').'</strong>');
$result2=ouwiki_diff_add_markers($html2,$added,'ouw_added',
'<strong class="accesshide">'.get_string('addedbegins','wiki').'</strong>',
'<strong class="accesshide">'.get_string('addedends','wiki').'</strong>');
return array($result1,$result2);
}