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/*
* Copyright (C) 2014 The Android Open Source Project
*
* 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.
*/
package com.android.inputmethod.latin.utils;
import com.android.inputmethod.latin.NgramContext;
import com.android.inputmethod.latin.NgramContext.WordInfo;
import com.android.inputmethod.latin.common.Constants;
import com.android.inputmethod.latin.settings.SpacingAndPunctuations;
import java.util.Arrays;
import java.util.regex.Pattern;
import javax.annotation.Nonnull;
public final class NgramContextUtils {
private NgramContextUtils() {
// Intentional empty constructor for utility class.
}
private static final Pattern SPACE_REGEX = Pattern.compile("\\s+");
// Get context information from nth word before the cursor. n = 1 retrieves the words
// immediately before the cursor, n = 2 retrieves the words before that, and so on. This splits
// on whitespace only.
// Also, it won't return words that end in a separator (if the nth word before the cursor
// ends in a separator, it returns information representing beginning-of-sentence).
// Example (when Constants.MAX_PREV_WORD_COUNT_FOR_N_GRAM is 2):
// (n = 1) "abc def|" -> abc, def
// (n = 1) "abc def |" -> abc, def
// (n = 1) "abc 'def|" -> empty, 'def
// (n = 1) "abc def. |" -> beginning-of-sentence
// (n = 1) "abc def . |" -> beginning-of-sentence
// (n = 2) "abc def|" -> beginning-of-sentence, abc
// (n = 2) "abc def |" -> beginning-of-sentence, abc
// (n = 2) "abc 'def|" -> empty. The context is different from "abc def", but we cannot
// represent this situation using NgramContext. See TODO in the method.
// TODO: The next example's result should be "abc, def". This have to be fixed before we
// retrieve the prior context of Beginning-of-Sentence.
// (n = 2) "abc def. |" -> beginning-of-sentence, abc
// (n = 2) "abc def . |" -> abc, def
// (n = 2) "abc|" -> beginning-of-sentence
// (n = 2) "abc |" -> beginning-of-sentence
// (n = 2) "abc. def|" -> beginning-of-sentence
@Nonnull
public static NgramContext getNgramContextFromNthPreviousWord(final CharSequence prev,
final SpacingAndPunctuations spacingAndPunctuations, final int n) {
if (prev == null) return NgramContext.EMPTY_PREV_WORDS_INFO;
final String[] w = SPACE_REGEX.split(prev);
final WordInfo[] prevWordsInfo = new WordInfo[Constants.MAX_PREV_WORD_COUNT_FOR_N_GRAM];
Arrays.fill(prevWordsInfo, WordInfo.EMPTY_WORD_INFO);
for (int i = 0; i < prevWordsInfo.length; i++) {
final int focusedWordIndex = w.length - n - i;
// Referring to the word after the focused word.
if ((focusedWordIndex + 1) >= 0 && (focusedWordIndex + 1) < w.length) {
final String wordFollowingTheNthPrevWord = w[focusedWordIndex + 1];
if (!wordFollowingTheNthPrevWord.isEmpty()) {
final char firstChar = wordFollowingTheNthPrevWord.charAt(0);
if (spacingAndPunctuations.isWordConnector(firstChar)) {
// The word following the focused word is starting with a word connector.
// TODO: Return meaningful context for this case.
break;
}
}
}
// If we can't find (n + i) words, the context is beginning-of-sentence.
if (focusedWordIndex < 0) {
prevWordsInfo[i] = WordInfo.BEGINNING_OF_SENTENCE_WORD_INFO;
break;
}
final String focusedWord = w[focusedWordIndex];
// If the word is, the context is beginning-of-sentence.
final int length = focusedWord.length();
if (length <= 0) {
prevWordsInfo[i] = WordInfo.BEGINNING_OF_SENTENCE_WORD_INFO;
break;
}
// If ends in a sentence separator, the context is beginning-of-sentence.
final char lastChar = focusedWord.charAt(length - 1);
if (spacingAndPunctuations.isSentenceSeparator(lastChar)) {
prevWordsInfo[i] = WordInfo.BEGINNING_OF_SENTENCE_WORD_INFO;
break;
}
// If ends in a word separator or connector, the context is unclear.
// TODO: Return meaningful context for this case.
if (spacingAndPunctuations.isWordSeparator(lastChar)
|| spacingAndPunctuations.isWordConnector(lastChar)) {
break;
}
prevWordsInfo[i] = new WordInfo(focusedWord);
}
return new NgramContext(prevWordsInfo);
}
}
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