/*
 * Diff Match and Patch
 *
 * Copyright 2010 geheimwerk.de.
 * http://code.google.com/p/google-diff-match-patch/
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Author: fraser@google.com (Neil Fraser)
 * ObjC port: jan@geheimwerk.de (Jan Weiß)
 * Refactoring & mangling: @inquisitivesoft (Harry Jordan)
 */


#import <CoreFoundation/CoreFoundation.h>
#import "DiffMatchPatchCFUtilities.h"

#import <regex.h>
#import <limits.h>


#define diff_UniCharMax (~(UniChar)0x00)


Boolean diff_regExMatch(CFStringRef text, const regex_t *re);
CFArrayRef diff_halfMatchICreate(CFStringRef longtext, CFStringRef shorttext, CFIndex i);
void diff_mungeHelper(CFStringRef token, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash, CFMutableStringRef chars);


Boolean diff_regExMatch(CFStringRef text, const regex_t *re)
{
	// TODO(jan): Using regex.h is far from optimal. Find an alternative.
	Boolean isMatch;
	const char *bytes;
	char *localBuffer = NULL;
	char *textCString = NULL;
	
	// We are only interested in line endings anyway so ASCII is fine.
	CFStringEncoding encoding = kCFStringEncodingASCII;

	bytes = CFStringGetCStringPtr(text, encoding);

	if(bytes == NULL) {
		Boolean success;
		CFIndex length;
		CFIndex usedBufferLength;
		CFIndex textLength = CFStringGetLength(text);
		CFRange rangeToProcess = CFRangeMake(0, textLength);

		success = (CFStringGetBytes(text, rangeToProcess, encoding, '?', false, NULL, LONG_MAX, &usedBufferLength) > 0);
		if(success) {
			length = usedBufferLength + 1;
			
			localBuffer = calloc(length, sizeof(char) );
			success = (CFStringGetBytes(text, rangeToProcess, encoding, '?', false, (UInt8 *)localBuffer, length, NULL) > 0);

			if(success) {
				textCString = localBuffer;
			}
		}
	} else {
		textCString = (char *)bytes;
	}

	if(textCString != NULL) {
		isMatch = (regexec(re, textCString, 0, NULL, 0) == 0);
	} else {
		isMatch = false;
		// check(0);
	}

	if(localBuffer != NULL) {
		free(localBuffer);
	}

	return isMatch;
}



/**
 * Determine the common prefix of two strings.
 * @param text1 First string.
 * @param text2 Second string.
 * @return The number of characters common to the start of each string.
 */

CFIndex diff_commonPrefix(CFStringRef text1, CFStringRef text2)
{
	// Performance analysis: http://neil.fraser.name/news/2007/10/09/
	CFIndex text1_length = CFStringGetLength(text1);
	CFIndex text2_length = CFStringGetLength(text2);

	CFStringInlineBuffer text1_inlineBuffer, text2_inlineBuffer;

	CFStringInitInlineBuffer(text1, &text1_inlineBuffer, CFRangeMake(0, text1_length) );
	CFStringInitInlineBuffer(text2, &text2_inlineBuffer, CFRangeMake(0, text2_length) );

	UniChar char1, char2;
	CFIndex numberOfCommonCharacters = MIN(text1_length, text2_length);

	for(CFIndex i = 0; i < numberOfCommonCharacters; i++) {
		char1 = CFStringGetCharacterFromInlineBuffer(&text1_inlineBuffer, i);
		char2 = CFStringGetCharacterFromInlineBuffer(&text2_inlineBuffer, i);

		if(char1 != char2) {
			return i;
		}
	}

	return numberOfCommonCharacters;
}



/**
 * Determine the common suffix of two strings.
 * @param text1 First string.
 * @param text2 Second string.
 * @return The number of characters common to the end of each string.
 */

CFIndex diff_commonSuffix(CFStringRef text1, CFStringRef text2)
{
	// Performance analysis: http://neil.fraser.name/news/2007/10/09/
	CFIndex text1_length = CFStringGetLength(text1);
	CFIndex text2_length = CFStringGetLength(text2);

	CFStringInlineBuffer text1_inlineBuffer, text2_inlineBuffer;

	CFStringInitInlineBuffer(text1, &text1_inlineBuffer, CFRangeMake(0, text1_length) );
	CFStringInitInlineBuffer(text2, &text2_inlineBuffer, CFRangeMake(0, text2_length) );

	UniChar char1, char2;
	CFIndex numberOfCommonCharacters = MIN(text1_length, text2_length);

	for(CFIndex i = 1; i <= numberOfCommonCharacters; i++) {
		char1 = CFStringGetCharacterFromInlineBuffer(&text1_inlineBuffer, (text1_length - i) );
		char2 = CFStringGetCharacterFromInlineBuffer(&text2_inlineBuffer, (text2_length - i) );

		if(char1 != char2) {
			return i - 1;
		}
	}
	
	return numberOfCommonCharacters;
}



/**
 * Determine if the suffix of one CFStringRef is the prefix of another.
 * @param text1 First CFStringRef.
 * @param text2 Second CFStringRef.
 * @return The number of characters common to the end of the first
 *     CFStringRef and the start of the second CFStringRef.
 */

CFIndex diff_commonOverlap(CFStringRef text1, CFStringRef text2)
{
	CFIndex common_overlap = 0;
	
	// Cache the text lengths to prevent multiple calls.
	CFIndex text1_length = CFStringGetLength(text1);
	CFIndex text2_length = CFStringGetLength(text2);

	// Eliminate the nil case.
	if(text1_length == 0 || text2_length == 0) {
		return 0;
	}
	
	// Truncate the longer CFStringRef.
	CFStringRef text1_trunc;
	CFStringRef text2_trunc;
	CFIndex text1_trunc_length;
	
	if(text1_length > text2_length) {
		text1_trunc_length = text2_length;
		text1_trunc = diff_CFStringCreateRightSubstring(text1, text1_length, text1_trunc_length);

		text2_trunc = CFRetain(text2);
	} else if(text1_length < text2_length) {
		text1_trunc_length = text1_length;
		text1_trunc = CFRetain(text1);

		CFIndex text2_trunc_length = text1_length;
		text2_trunc = diff_CFStringCreateLeftSubstring(text2, text2_trunc_length);
	} else {
		text1_trunc_length = text1_length;
		text1_trunc = CFRetain(text1);
		text2_trunc = CFRetain(text2);
	}

	CFIndex text_length = MIN(text1_length, text2_length);
	// Quick check for the worst case.
	if(CFStringCompare(text1_trunc, text2_trunc, 0) == kCFCompareEqualTo) {
		common_overlap = text_length;
	} else {
		// Start by looking for a single character match
		// and increase length until no match is found.
		// Performance analysis: http://neil.fraser.name/news/2010/11/04/
		CFIndex best = 0;
		CFIndex length = 1;
		while(true) {
			CFStringRef pattern = diff_CFStringCreateRightSubstring(text1_trunc, text1_trunc_length, length);
			CFRange foundRange = CFStringFind(text2_trunc, pattern, 0);
			CFRelease(pattern);

			CFIndex found =  foundRange.location;
			if(found == kCFNotFound) {
				common_overlap = best;
				break;
			}
			length += found;

			CFStringRef text1_sub = diff_CFStringCreateRightSubstring(text1_trunc, text1_trunc_length, length);
			CFStringRef text2_sub = diff_CFStringCreateLeftSubstring(text2_trunc, length);

			if( found == 0 || (CFStringCompare(text1_sub, text2_sub, 0) == kCFCompareEqualTo) ) {
				best = length;
				length++;
			}

			CFRelease(text1_sub);
			CFRelease(text2_sub);
		}
	}

	CFRelease(text1_trunc);
	CFRelease(text2_trunc);
	return common_overlap;
}



/**
 * Do the two texts share a Substring which is at least half the length of
 * the longer text?
 * This speedup can produce non-minimal diffs.
 * @param text1 First CFStringRef.
 * @param text2 Second CFStringRef.
 * @return Five element CFStringRef array, containing the prefix of text1, the
 *     suffix of text1, the prefix of text2, the suffix of text2 and the
 *     common middle.   Or NULL if there was no match.
 */

CFArrayRef diff_halfMatchCreate(CFStringRef text1, CFStringRef text2)
{
	CFStringRef longtext = CFStringGetLength(text1) > CFStringGetLength(text2) ? text1 : text2;
	CFStringRef shorttext = CFStringGetLength(text1) > CFStringGetLength(text2) ? text2 : text1;
	
	if(CFStringGetLength(longtext) < 4 || CFStringGetLength(shorttext) * 2 < CFStringGetLength(longtext)) {
		return NULL;                                                                                                                                                                                                                                         // Pointless.
	}

	// First check if the second quarter is the seed for a half-match.
	CFArrayRef hm1 = diff_halfMatchICreate(longtext, shorttext, (CFStringGetLength(longtext) + 3) / 4);
	
	// Check again based on the third quarter.
	CFArrayRef hm2 = diff_halfMatchICreate(longtext, shorttext, (CFStringGetLength(longtext) + 1) / 2);
	
	CFArrayRef hm;
	if(hm1 == NULL && hm2 == NULL) {
		return NULL;
	} else if(hm2 == NULL) {
		hm = CFRetain(hm1);
	} else if(hm1 == NULL) {
		hm = CFRetain(hm2);
	} else {
		// Both matched.  Select the longest.
		hm = CFStringGetLength(CFArrayGetValueAtIndex(hm1, 4) ) > CFStringGetLength(CFArrayGetValueAtIndex(hm2, 4) ) ? CFRetain(hm1) : CFRetain(hm2);
	}

	if(hm1 != NULL) {
		CFRelease(hm1);
	}
	if(hm2 != NULL) {
		CFRelease(hm2);
	}

	// A half-match was found, sort out the return data.
	if(CFStringGetLength(text1) > CFStringGetLength(text2)) {
		return hm;
		// return new CFStringRef[]{hm[0], hm[1], hm[2], hm[3], hm[4]};
	} else {
		//    { hm[0], hm[1], hm[2], hm[3], hm[4] }
		// => { hm[2], hm[3], hm[0], hm[1], hm[4] }

		CFMutableArrayRef hm_mutable = CFArrayCreateMutableCopy(kCFAllocatorDefault, CFArrayGetCount(hm), hm);
		CFRelease(hm);

		CFArrayExchangeValuesAtIndices(hm_mutable, 0, 2);
		CFArrayExchangeValuesAtIndices(hm_mutable, 1, 3);
		return hm_mutable;
	}
}



/**
 * Does a Substring of shorttext exist within longtext such that the
 * Substring is at least half the length of longtext?
 * @param longtext Longer CFStringRef.
 * @param shorttext Shorter CFStringRef.
 * @param i Start index of quarter length Substring within longtext.
 * @return Five element CFStringRef array, containing the prefix of longtext, the
 *     suffix of longtext, the prefix of shorttext, the suffix of shorttext
 *     and the common middle.   Or NULL if there was no match.
 */

CFArrayRef diff_halfMatchICreate(CFStringRef longtext, CFStringRef shorttext, CFIndex i)
{
	// Start with a 1/4 length Substring at position i as a seed.
	CFStringRef seed = diff_CFStringCreateSubstring(longtext, i, CFStringGetLength(longtext) / 4);
	CFIndex j = -1;
	CFStringRef best_common = CFSTR("");
	CFStringRef best_longtext_a = CFSTR(""), best_longtext_b = CFSTR("");
	CFStringRef best_shorttext_a = CFSTR(""), best_shorttext_b = CFSTR("");

	CFStringRef longtext_substring, shorttext_substring;
	CFIndex shorttext_length = CFStringGetLength(shorttext);
	CFRange resultRange;
	CFRange rangeToSearch;

	rangeToSearch.length = shorttext_length - (j + 1);
	rangeToSearch.location = j + 1;

	while(j < CFStringGetLength(shorttext) && (CFStringFindWithOptions(shorttext, seed, rangeToSearch, 0, &resultRange) == true) ) {
		j = resultRange.location;
		rangeToSearch.length = shorttext_length - (j + 1);
		rangeToSearch.location = j + 1;

		longtext_substring = diff_CFStringCreateSubstringWithStartIndex(longtext, i);
		shorttext_substring = diff_CFStringCreateSubstringWithStartIndex(shorttext, j);

		CFIndex prefixLength = diff_commonPrefix(longtext_substring, shorttext_substring);

		CFRelease(longtext_substring);
		CFRelease(shorttext_substring);

		longtext_substring = diff_CFStringCreateLeftSubstring(longtext, i);
		shorttext_substring = diff_CFStringCreateLeftSubstring(shorttext, j);

		CFIndex suffixLength = diff_commonSuffix(longtext_substring, shorttext_substring);

		CFRelease(longtext_substring);
		CFRelease(shorttext_substring);

		if(CFStringGetLength(best_common) < suffixLength + prefixLength) {
			CFRelease(best_common);
			CFRelease(best_longtext_a);
			CFRelease(best_longtext_b);
			CFRelease(best_shorttext_a);
			CFRelease(best_shorttext_b);

			best_common = diff_CFStringCreateSubstring(shorttext, j - suffixLength, suffixLength + prefixLength);

			best_longtext_a = diff_CFStringCreateLeftSubstring(longtext, i - suffixLength);
			best_longtext_b = diff_CFStringCreateSubstringWithStartIndex(longtext, i + prefixLength);
			best_shorttext_a = diff_CFStringCreateLeftSubstring(shorttext, j - suffixLength);
			best_shorttext_b = diff_CFStringCreateSubstringWithStartIndex(shorttext, j + prefixLength);
		}
	}

	CFRelease(seed);

	CFArrayRef halfMatchIArray;
	if(CFStringGetLength(best_common) * 2 >= CFStringGetLength(longtext) ) {
		const CFStringRef values[] = {
			best_longtext_a,  best_longtext_b,
			best_shorttext_a, best_shorttext_b,best_common
		};
		
		halfMatchIArray = CFArrayCreate(kCFAllocatorDefault, (const void **)values, ( sizeof(values) / sizeof(values[0]) ), &kCFTypeArrayCallBacks);
	} else {
		halfMatchIArray = NULL;
	}

	CFRelease(best_common);
	CFRelease(best_longtext_a);
	CFRelease(best_longtext_b);
	CFRelease(best_shorttext_a);
	CFRelease(best_shorttext_b);

	return halfMatchIArray;
}


void diff_mungeHelper(CFStringRef token, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash, CFMutableStringRef chars)
{
	CFIndex hash;
	
	if(CFDictionaryGetValueIfPresent(tokenHash, token, (const void **)&hash) ) {
		const UniChar hashChar = (UniChar)hash;
		CFStringAppendCharacters(chars, &hashChar, 1);
	} else {
		CFArrayAppendValue(tokenArray, token);
		hash = CFArrayGetCount(tokenArray) - 1;
		NSCAssert(!(hash <= diff_UniCharMax), @"Hash value has exceeded UniCharMax!");
		CFDictionaryAddValue(tokenHash, token, (void *)hash);
		const UniChar hashChar = (UniChar)hash;
		CFStringAppendCharacters(chars, &hashChar, 1);
	}
}


CF_INLINE void diff_mungeTokenForRange(CFStringRef text, CFRange tokenRange, CFMutableStringRef chars, CFMutableDictionaryRef tokenHash, CFMutableArrayRef tokenArray)
{
	CFStringRef token = CFStringCreateWithSubstring(kCFAllocatorDefault, text, tokenRange);
	diff_mungeHelper(token, tokenArray, tokenHash, chars);
	CFRelease(token);
}



/**
 * Split a text into a list of strings.   Reduce the texts to a CFStringRef of
 * hashes where each Unicode character represents one line.
 * @param text CFString to encode.
 * @param lineArray CFMutableArray of unique strings.
 * @param lineHash Map of strings to indices.
 * @return Encoded CFStringRef.
 */

CFStringRef diff_linesToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef lineArray, CFMutableDictionaryRef lineHash)
{
	CFRange lineStartRange;
	CFRange lineEndRange;
	lineStartRange.location = 0;
	lineEndRange.location = -1;
	CFStringRef line;
	CFMutableStringRef chars = CFStringCreateMutable(kCFAllocatorDefault, 0);

	CFIndex textLength = CFStringGetLength(text);

	// Walk the text, pulling out a Substring for each line.
	// CFStringCreateArrayBySeparatingStrings(kCFAllocatorDefault, text, CFSTR("\n")) would temporarily double our memory footprint.
	// Modifying text would create many large strings.
	while(lineEndRange.location < textLength - 1) {
		lineStartRange.length = textLength - lineStartRange.location;

		if(CFStringFindWithOptions(text, CFSTR("\n"), lineStartRange, 0, &lineEndRange) == false) {
			lineEndRange.location = textLength - 1;
		}
		
		line = diff_CFStringCreateSubstring(text, lineStartRange.location, lineEndRange.location + 1 - lineStartRange.location);
		lineStartRange.location = lineEndRange.location + 1;
		
		diff_mungeHelper(line, lineArray, lineHash, chars);

		CFRelease(line);
	}

	return chars;
}



/**
 * Split a text into a list of strings.   Reduce the texts to a CFStringRef of
 * hashes where where each Unicode character represents one token (or boundary between tokens).
 * @param text CFString to encode.
 * @param tokenArray CFMutableArray of unique strings.
 * @param tokenHash Map of strings to indices.
 * @return Encoded CFStringRef.
 */

CFStringRef diff_tokensToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash, CFOptionFlags tokenizerOptions)
{
	CFMutableStringRef chars = CFStringCreateMutable(kCFAllocatorDefault, 0);
	CFIndex textLength = CFStringGetLength(text);
	CFRange tokenizerRange = CFRangeMake(0, textLength);
	CFStringTokenizerRef tokenizer = CFStringTokenizerCreate(kCFAllocatorDefault, text, tokenizerRange, tokenizerOptions, NULL);

	// Set tokenizer to the start of the string.
	CFStringTokenizerTokenType tokenType = CFStringTokenizerGoToTokenAtIndex(tokenizer, 0);

	// Walk the text, pulling out a substring for each token (or boundary between tokens).
	// A token is either a word, sentence, paragraph or line depending on what tokenizerOptions is set to.
	CFRange tokenRange;
	CFIndex prevTokenRangeMax = 0;

	while(tokenType != kCFStringTokenizerTokenNone) {
		tokenRange = CFStringTokenizerGetCurrentTokenRange(tokenizer);

		if(tokenRange.location > prevTokenRangeMax) {
			// This probably is a bug in the tokenizer: for some reason, gaps in the tokenization can appear.
			// One particular example is the tokenizer skipping a line feed ('\n') directly after a string of Chinese characters
			CFRange gapRange = CFRangeMake(prevTokenRangeMax, (tokenRange.location - prevTokenRangeMax) );
			diff_mungeTokenForRange(text, gapRange, chars, tokenHash, tokenArray);
		}

		diff_mungeTokenForRange(text, tokenRange, chars, tokenHash, tokenArray);

		tokenType = CFStringTokenizerAdvanceToNextToken(tokenizer);
		prevTokenRangeMax = (tokenRange.location + tokenRange.length);
	}

	CFRelease(tokenizer);
	
	return chars;
}



/**
 * Split a text into a list of strings.  Reduce the texts to a CFStringRef of
 * hashes where where each Unicode character represents the substring for a CFRange.
 * @param text CFString to encode.
 * @param substringArray CFMutableArray of unique strings.
 * @param substringHash Map of strings to indices.
 * @param ranges C array of CFRange structs determining the subranges to hash.
 * @param ranges_count Count of the CFRange structs contained in ranges.
 * @return Encoded CFStringRef.
 */

CFStringRef diff_rangesToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef substringArray, CFMutableDictionaryRef substringHash, CFRange *ranges, size_t ranges_count)
{
	CFMutableStringRef chars = CFStringCreateMutable(kCFAllocatorDefault, 0);

	for(size_t i = 0; i < ranges_count; i++) {
		CFRange substringRange = ranges[i];
		
		diff_mungeTokenForRange(text, substringRange, chars, substringHash, substringArray);
	}

	return chars;
}



/**
 * Split a text into a list of strings.   Reduce the texts to a CFStringRef of
 * hashes where where each Unicode character represents one word (or boundary between words).
 * @param text CFString to encode.
 * @param lineArray CFMutableArray of unique strings.
 * @param lineHash Map of strings to indices.
 * @return Encoded CFStringRef.
 */

CFStringRef diff_wordsToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash)
{
	return diff_tokensToCharsMungeCFStringCreate(text, tokenArray, tokenHash, kCFStringTokenizerUnitWordBoundary);
}



/**
 * Split a text into a list of strings.   Reduce the texts to a CFStringRef of
 * hashes where where each Unicode character represents one sentence.
 * @param text CFString to encode.
 * @param lineArray CFMutableArray of unique strings.
 * @param lineHash Map of strings to indices.
 * @return Encoded CFStringRef.
 */

CFStringRef diff_sentencesToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash)
{
	return diff_tokensToCharsMungeCFStringCreate(text, tokenArray, tokenHash, kCFStringTokenizerUnitSentence);
}



/**
 * Split a text into a list of strings.   Reduce the texts to a CFStringRef of
 * hashes where where each Unicode character represents one paragraph.
 * @param text CFString to encode.
 * @param lineArray CFMutableArray of unique strings.
 * @param lineHash Map of strings to indices.
 * @return Encoded CFStringRef.
 */

CFStringRef diff_paragraphsToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash)
{
	return diff_tokensToCharsMungeCFStringCreate(text, tokenArray, tokenHash, kCFStringTokenizerUnitParagraph);
}



/**
 * Split a text into a list of strings.   Reduce the texts to a CFStringRef of
 * hashes where each Unicode character represents one text fragment delimitered by line breaks (including the trailing line break characters if any).
 * In this context “line break” does not refere to “something you get when you press the return-key”.
 * Instead it the refers to “line break boundaries” as defined in “UAX #14: Unicode Line Breaking Algorithm” (http://www.unicode.org/reports/tr14/).
 * @param text CFString to encode.
 * @param lineArray CFMutableArray of unique strings.
 * @param lineHash Map of strings to indices.
 * @return Encoded CFStringRef.
 */
 
CFStringRef diff_lineBreakDelimiteredToCharsMungeCFStringCreate(CFStringRef text, CFMutableArrayRef tokenArray, CFMutableDictionaryRef tokenHash)
{
	return diff_tokensToCharsMungeCFStringCreate(text, tokenArray, tokenHash, kCFStringTokenizerUnitLineBreak);
}


CFStringRef diff_charsToTokenCFStringCreate(CFStringRef charsString, CFArrayRef tokenArray)
{
	CFMutableStringRef text = CFStringCreateMutable(kCFAllocatorDefault, 0);
	CFIndex hash_count = CFStringGetLength(charsString);
	
	const UniChar *hash_chars;
	UniChar *hash_buffer = NULL;
	diff_CFStringPrepareUniCharBuffer(charsString, &hash_chars, &hash_buffer, CFRangeMake(0, hash_count) );
	
	for(CFIndex i = 0; i < hash_count; i++) {
		CFIndex tokenHash = hash_chars[i];
		CFStringRef token = CFArrayGetValueAtIndex(tokenArray, tokenHash);
		CFStringAppend(text, token);
	}
	
	if(hash_buffer != NULL) {
		free(hash_buffer);
	}
	
	return text;
}



/**
 * Given two strings, compute a score representing whether the internal
 * boundary falls on logical boundaries.
 * Scores range from 6 (best) to 0 (worst).
 * @param one First CFStringRef.
 * @param two Second CFStringRef.
 * @return The score.
 */

CFIndex diff_cleanupSemanticScore(CFStringRef one, CFStringRef two)
{
	static CFCharacterSetRef diff_alphaNumericSet = NULL;
	static CFCharacterSetRef diff_whiteSpaceSet = NULL;
	static CFCharacterSetRef diff_controlSet = NULL;
	static regex_t diff_blankLineEndRegEx;
	static regex_t diff_blankLineStartRegEx;
	
	static dispatch_once_t setupCleanupSemanticScoreToken;
	dispatch_once(&setupCleanupSemanticScoreToken, ^{
		diff_alphaNumericSet = CFCharacterSetGetPredefined(kCFCharacterSetAlphaNumeric);
		diff_whiteSpaceSet = CFCharacterSetGetPredefined(kCFCharacterSetWhitespaceAndNewline);
		diff_controlSet = CFCharacterSetGetPredefined(kCFCharacterSetControl);
		
		// Define some regex patterns for matching boundaries.
		int status = regcomp(&diff_blankLineEndRegEx, "\n\r?\n$", REG_EXTENDED | REG_NOSUB);
		NSCAssert(status == 0, @"Failed to compile the \n\r?\n$ regex");
		
		status = regcomp(&diff_blankLineStartRegEx, "^\r?\n\r?\n", REG_EXTENDED | REG_NOSUB);
		NSCAssert(status == 0, @"Failed to compile the ^\r?\n\r?\n regex");
	});
	
	if(CFStringGetLength(one) == 0 || CFStringGetLength(two) == 0) {
		// Edges are the best.
		return 6;
	}

	// Each port of this function behaves slightly differently due to
	// subtle differences in each language's definition of things like
	// 'whitespace'.  Since this function's purpose is largely cosmetic,
	// the choice has been made to use each language's native features
	// rather than force total conformity.
	
	UniChar char1 = CFStringGetCharacterAtIndex(one, (CFStringGetLength(one) - 1) );
	UniChar char2 = CFStringGetCharacterAtIndex(two, 0);
	Boolean nonAlphaNumeric1 = !CFCharacterSetIsCharacterMember(diff_alphaNumericSet, char1);
	Boolean nonAlphaNumeric2 = !CFCharacterSetIsCharacterMember(diff_alphaNumericSet, char2);
	Boolean whitespace1 = nonAlphaNumeric1 && CFCharacterSetIsCharacterMember(diff_whiteSpaceSet, char1);
	Boolean whitespace2 = nonAlphaNumeric2 && CFCharacterSetIsCharacterMember(diff_whiteSpaceSet, char2);
	Boolean lineBreak1 = whitespace1 && CFCharacterSetIsCharacterMember(diff_controlSet, char1);
	Boolean lineBreak2 = whitespace2 && CFCharacterSetIsCharacterMember(diff_controlSet, char2);
	Boolean blankLine1 = lineBreak1 && diff_regExMatch(one, &diff_blankLineEndRegEx);
	Boolean blankLine2 = lineBreak2 && diff_regExMatch(two, &diff_blankLineStartRegEx);
	
	if(blankLine1 || blankLine2) {
		// Five points for blank lines.
		return 5;
	} else if(lineBreak1 || lineBreak2) {
		// Four points for line breaks.
		return 4;
	} else if(nonAlphaNumeric1 && !whitespace1 && whitespace2) {
		// Three points for end of sentences.
		return 3;
	} else if(whitespace1 || whitespace2) {
		// Two points for whitespace.
		return 2;
	} else if(nonAlphaNumeric1 || nonAlphaNumeric2) {
		// One point for non-alphanumeric.
		return 1;
	}
	return 0;
}