/*
*******************************************************************************
* Copyright (C) 1996-2008, International Business Machines Corporation and *
* others. All Rights Reserved. *
*******************************************************************************
*/
package com.ibm.icu.text;
import com.ibm.icu.impl.Assert;
import com.ibm.icu.text.UnicodeSet;
import java.util.Stack;
import java.io.InputStream;
import java.text.CharacterIterator;
import java.io.IOException;
class ThaiBreakIterator extends DictionaryBasedBreakIterator {
/* Helper class for improving readability of the Thai word break
* algorithm.
*/
static class PossibleWord {
// List size, limited by the maximum number of words in the dictionary
// that form a nested sequence.
private final int POSSIBLE_WORD_LIST_MAX = 20;
//list of word candidate lengths, in increasing length order
private int lengths[];
private int count[]; // Count of candidates
private int prefix; // The longeset match with a dictionary word
private int offset; // Offset in the text of these candidates
private int mark; // The preferred candidate's offset
private int current; // The candidate we're currently looking at
// Default constructor
public PossibleWord() {
lengths = new int[POSSIBLE_WORD_LIST_MAX];
count = new int[1]; // count needs to be an array of 1 so that it can be pass as reference
offset = -1;
}
// Fill the list of candidates if needed, select the longest, and return the number found
public int candidates(CharacterIterator fIter, BreakCTDictionary dict, int rangeEnd) {
int start = fIter.getIndex();
if (start != offset) {
offset = start;
prefix = dict.matches(fIter, rangeEnd - start, lengths, count, lengths.length);
// Dictionary leaves text after longest prefix, not longest word. Back up.
if (count[0] <= 0) {
fIter.setIndex(start);
}
}
if (count[0] > 0) {
fIter.setIndex(start + lengths[count[0]-1]);
}
current = count[0] - 1;
mark = current;
return count[0];
}
// Select the currently marked candidate, point after it in the text, and invalidate self
public int acceptMarked(CharacterIterator fIter) {
fIter.setIndex(offset + lengths[mark]);
return lengths[mark];
}
// Backup from the current candidate to the next shorter one; rreturn true if that exists
// and point the text after it
public boolean backUp(CharacterIterator fIter) {
if (current > 0) {
fIter.setIndex(offset + lengths[--current]);
return true;
}
return false;
}
// Return the longest prefix this candidate location shares with a dictionary word
public int longestPrefix() {
return prefix;
}
// Mark the current candidate as the one we like
public void markCurrent() {
mark = current;
}
}
private static UnicodeSet fThaiWordSet;
private static UnicodeSet fEndWordSet;
private static UnicodeSet fBeginWordSet;
private static UnicodeSet fSuffixSet;
private static UnicodeSet fMarkSet;
private BreakCTDictionary fDictionary;
// Constants for ThaiBreakIterator
// How many words in a row are "good enough"?
private static final byte THAI_LOOKAHEAD = 3;
// Will not combine a non-word with a preceding dictionary word longer than this
private static final byte THAI_ROOT_COMBINE_THRESHOLD = 3;
// Will not combine a non-word that shares at least this much prefix with a
// dictionary word with a preceding word
private static final byte THAI_PREFIX_COMBINE_THRESHOLD = 3;
// Ellision character
private static final char THAI_PAIYANNOI = 0x0E2F;
// Repeat character
private static final char THAI_MAIYAMOK = 0x0E46;
// Minimum word size
private static final byte THAI_MIN_WORD = 2;
// Minimum number of characters for two words
//private final int THAI_MIN_WORD_SPAN = THAI_MIN_WORD * 2;
static {
// Initialize UnicodeSets
fThaiWordSet = new UnicodeSet();
fMarkSet = new UnicodeSet();
fEndWordSet = new UnicodeSet();
fBeginWordSet = new UnicodeSet();
fSuffixSet = new UnicodeSet();
fThaiWordSet.applyPattern(new String("[[:Thai:]&[:LineBreak=SA:]]"));
fThaiWordSet.compact();
fMarkSet.applyPattern(new String("[[:Thai:]&[:LineBreak=SA:]&[:M:]]"));
fMarkSet.add(0x0020);
fEndWordSet = fThaiWordSet;
fEndWordSet.remove(0x0E31); // MAI HAN-AKAT
fEndWordSet.remove(0x0E40, 0x0E44); // SARA E through SARA AI MAIMALAI
fBeginWordSet.add(0x0E01, 0x0E2E); //KO KAI through HO NOKHUK
fBeginWordSet.add(0x0E40, 0x0E44); // SARA E through SARA AI MAIMALAI
fSuffixSet.add(THAI_PAIYANNOI);
fSuffixSet.add(THAI_MAIYAMOK);
// Compact for caching
fMarkSet.compact();
fEndWordSet.compact();
fBeginWordSet.compact();
fSuffixSet.compact();
// Freeze the static UnicodeSet
fThaiWordSet.freeze();
fMarkSet.freeze();
fEndWordSet.freeze();
fBeginWordSet.freeze();
fSuffixSet.freeze();
}
public ThaiBreakIterator(InputStream ruleStream, InputStream dictionaryStream) throws IOException {
super(ruleStream);
// Initialize diciontary
fDictionary = new BreakCTDictionary(dictionaryStream);
}
/**
* This is the implementation function for next().
* @internal
* @deprecated This API is ICU internal only.
*/
protected int handleNext() {
CharacterIterator text = getText();
// if there are no cached break positions, or if we've just moved
// off the end of the range covered by the cache, we have to dump
// and possibly regenerate the cache
if (cachedBreakPositions == null || positionInCache == cachedBreakPositions.length - 1) {
// start by using the inherited handleNext() to find a tentative return
// value. dictionaryCharCount tells us how many dictionary characters
// we passed over on our way to the tentative return value
int startPos = text.getIndex();
fDictionaryCharCount = 0;
int result = super.handleNext();
// if we passed over more than one dictionary character, then we use
// divideUpDictionaryRange() to regenerate the cached break positions
// for the new range
if (fDictionaryCharCount > 1 && result - startPos > 1) {
divideUpDictionaryRange(startPos, result);
}
// otherwise, the value we got back from the inherited fuction
// is our return value, and we can dump the cache
else {
cachedBreakPositions = null;
return result;
}
}
// if the cache of break positions has been regenerated (or existed all
// along), then just advance to the next break position in the cache
// and return it
if (cachedBreakPositions != null) {
++positionInCache;
text.setIndex(cachedBreakPositions[positionInCache]);
return cachedBreakPositions[positionInCache];
}
Assert.assrt(false);
return -9999; // SHOULD NEVER GET HERE!
}
/**
* Divide up a range of known dictionary characters.
*
* @param rangeStart The start of the range of dictionary characters
* @param rangeEnd The end of the range of dictionary characters
* @return The number of breaks found
*/
private int divideUpDictionaryRange(int rangeStart, int rangeEnd) {
if ((rangeEnd - rangeStart) < THAI_MIN_WORD) {
return 0; // Not enough chacters for word
}
CharacterIterator fIter = getText();
int wordsFound = 0;
int wordLength;
int current;
Stack foundBreaks = new Stack();
PossibleWord words[] = new PossibleWord[THAI_LOOKAHEAD];
for (int i = 0; i < THAI_LOOKAHEAD; i++) {
words[i] = new PossibleWord();
}
int uc;
fIter.setIndex(rangeStart);
while ((current = fIter.getIndex()) < rangeEnd) {
wordLength = 0;
//Look for candidate words at the current position
int candidates = words[wordsFound%THAI_LOOKAHEAD].candidates(fIter, fDictionary, rangeEnd);
// If we found exactly one, use that
if (candidates == 1) {
wordLength = words[wordsFound%THAI_LOOKAHEAD].acceptMarked(fIter);
wordsFound += 1;
}
// If there was more than one, see which one can take use forward the most words
else if (candidates > 1) {
boolean foundBest = false;
// If we're already at the end of the range, we're done
if (fIter.getIndex() < rangeEnd) {
do {
int wordsMatched = 1;
if (words[(wordsFound+1)%THAI_LOOKAHEAD].candidates(fIter, fDictionary, rangeEnd) > 0) {
if (wordsMatched < 2) {
// Followed by another dictionary word; mark first word as a good candidate
words[wordsFound%THAI_LOOKAHEAD].markCurrent();
wordsMatched = 2;
}
// If we're already at the end of the range, we're done
if (fIter.getIndex() >= rangeEnd) {
break;
}
// See if any of the possible second words is followed by a third word
do {
// If we find a third word, stop right away
if (words[(wordsFound+2)%THAI_LOOKAHEAD].candidates(fIter, fDictionary, rangeEnd) > 0) {
words[wordsFound%THAI_LOOKAHEAD].markCurrent();
foundBest = true;
break;
}
} while (words[(wordsFound+1)%THAI_LOOKAHEAD].backUp(fIter));
}
} while (words[wordsFound%THAI_LOOKAHEAD].backUp(fIter) && !foundBest);
}
/* foundBest: */wordLength = words[wordsFound%THAI_LOOKAHEAD].acceptMarked(fIter);
wordsFound += 1;
}
// We come here after having either found a word or not. We look ahead to the
// next word. If it's not a dictionary word, we will combine it with the word we
// just found (if there is one), but only if the preceding word does not exceed
// the threshold.
// The text iterator should now be positioned at the end of the word we found.
if (fIter.getIndex() < rangeEnd && wordLength < THAI_ROOT_COMBINE_THRESHOLD) {
// If it is a dictionary word, do nothing. If it isn't, then if there is
// no preceding word, or the non-word shares less than the minimum threshold
// of characters with a dictionary word, then scan to resynchronize
if (words[wordsFound%THAI_LOOKAHEAD].candidates(fIter, fDictionary, rangeEnd) <= 0 &&
(wordLength == 0 ||
words[wordsFound%THAI_LOOKAHEAD].longestPrefix() < THAI_PREFIX_COMBINE_THRESHOLD)) {
// Look for a plausible word boundary
int remaining = rangeEnd - (current + wordLength);
int pc = fIter.current();
int chars = 0;
for (;;) {
fIter.next();
uc = fIter.current();
chars += 1;
if (--remaining <= 0) {
break;
}
if (fEndWordSet.contains(pc) && fBeginWordSet.contains(uc)) {
// Maybe. See if it's in the dictionary.
// Note: In the original Apple code, checked that the next
// two characters after uc were not 0x0E4C THANTHAKHAT before
// checking the dictionary. That is just a performance filter,
// but it's not clear it's faster than checking the trie
int candidate = words[(wordsFound+1)%THAI_LOOKAHEAD].candidates(fIter, fDictionary, rangeEnd);
fIter.setIndex(current+wordLength+chars);
if (candidate > 0) {
break;
}
}
pc = uc;
}
// Bump the word cound if there wasn't already one
if (wordLength <= 0) {
wordsFound += 1;
}
// Update the length with the passed-over characters
wordLength += chars;
} else {
// Backup to where we were for next iteration
fIter.setIndex(current+wordLength);
}
}
// Never stop before a combining mark.
int currPos;
while ((currPos = fIter.getIndex()) < rangeEnd && fMarkSet.contains(fIter.current())) {
fIter.next();
wordLength += fIter.getIndex() - currPos;
}
// Look ahead for possible suffixes if a dictionary word does not follow.
// We do this in code rather than using a rule so that the heuristic
// resynch continues to function. For example, one of the suffix characters
// could be a typo in the middle of a word.
if (fIter.getIndex() < rangeEnd && wordLength > 0) {
if (words[wordsFound%THAI_LOOKAHEAD].candidates(fIter, fDictionary, rangeEnd) <= 0 &&
fSuffixSet.contains(uc = fIter.current())) {
if (uc == THAI_PAIYANNOI) {
if (!fSuffixSet.contains(fIter.previous())) {
// Skip over previous end and PAIYANNOI
fIter.next();
fIter.next();
wordLength += 1;
uc = fIter.current();
} else {
// Restore prior position
fIter.next();
}
}
if (uc == THAI_MAIYAMOK) {
if (fIter.previous() != THAI_MAIYAMOK) {
// Skip over previous end and MAIYAMOK
fIter.next();
fIter.next();
wordLength += 1;
} else {
// restore prior position
fIter.next();
}
}
} else {
fIter.setIndex(current+wordLength);
}
}
// Did we find a word on this iteration? If so, push it on the break stack
if (wordLength > 0) {
foundBreaks.push(new Integer(current+wordLength));
}
}
// Don't return a break for the end of the dictionary range if there is one there
if (((Integer)foundBreaks.peek()).intValue() >= rangeEnd) {
foundBreaks.pop();
wordsFound -= 1;
}
// Store the break points in cachedBreakPositions.
cachedBreakPositions = new int[foundBreaks.size() + 2];
cachedBreakPositions[0] = rangeStart;
int i;
for (i = 0; i < foundBreaks.size(); i++) {
cachedBreakPositions[i + 1] = ((Integer)foundBreaks.elementAt(i)).intValue();
}
cachedBreakPositions[i + 1] = rangeEnd;
positionInCache = 0;
return wordsFound;
}
}