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// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Defines an iterator class that enumerates words supported by our spellchecker
// from multi-language text. This class is used for filtering out characters
// not supported by our spellchecker.
#pragma once
#include <string>
#include "unicode/ubrk.h"
#include "unicode/uscript.h"
#include "base/basictypes.h"
#include "base/string16.h"
// A class which encapsulates language-specific operations used by
// SpellcheckWordIterator. When we set the spellchecker language, this class
// creates rule sets that filter out the characters not supported by the
// spellchecker. (Please read the comment in the SpellcheckWordIterator class
// about how to use this class.)
class SpellcheckCharAttribute {
// Sets the language of the spellchecker. When this function is called with an
// ISO language code, this function creates the custom rule-sets used by
// the ICU break iterator so it can extract only words used by the language.
// GetRuleSet() returns the rule-sets created in this function.
void SetDefaultLanguage(const std::string& language);
// Returns a custom rule-set string used by the ICU break iterator. This class
// has two rule-sets, one splits a contraction and the other does not, so we
// can split a concaticated word (e.g. "seven-year-old") into words (e.g.
// "seven", "year", and "old") and check their spellings. The result stirng is
// encoded in UTF-16 since ICU needs UTF-16 strings.
string16 GetRuleSet(bool allow_contraction) const;
// Outputs a character only if it is a word character. (Please read the
// comments in CreateRuleSets() why we need this function.)
bool OutputChar(UChar c, string16* output) const;
// Creates the rule-sets that return words possibly used by the given
// language. Unfortunately, these rule-sets are not perfect and have some
// false-positives. For example, they return combined accent marks even though
// we need English words only. We call OutputCharacter() to filter out such
// false-positive characters.
void CreateRuleSets(const std::string& language);
// Outputs a character only if it is one used by the given language. These
// functions are called from OutputChar().
bool OutputArabic(UChar c, string16* output) const;
bool OutputHangul(UChar c, string16* output) const;
bool OutputHebrew(UChar c, string16* output) const;
bool OutputDefault(UChar c, string16* output) const;
// The custom rule-set strings used by ICU break iterator. Since it is not so
// easy to create custom rule-sets from an ISO language code, this class
// saves these rule-set strings created when we set the language.
string16 ruleset_allow_contraction_;
string16 ruleset_disallow_contraction_;
// The script code used by this language.
UScriptCode script_code_;
// A class which extracts words that can be checked for spelling from a
// multi-language string. The ICU word-break iterator does not discard some
// punctuation characters attached to a word. For example, when we set a word
// "_hello_" to a word-break iterator, it just returns "_hello_". Neither does
// it discard characters not used by the language. For example, it returns
// Russian words even though we need English words only. To extract only the
// words that our spellchecker can check their spellings, this class uses custom
// rule-sets created by the SpellcheckCharAttribute class. Also, this class
// normalizes extracted words so our spellchecker can check the spellings of
// words that include ligatures, combined characters, full-width characters,
// etc. This class uses UTF-16 strings as its input and output strings since
// UTF-16 is the native encoding of ICU and avoid unnecessary conversions
// when changing the encoding of this string for our spellchecker. (Chrome can
// use two or more spellcheckers and we cannot assume their encodings.)
// The following snippet is an example that extracts words with this class.
// // Creates the language-specific attributes for US English.
// SpellcheckCharAttribute attribute;
// attribute.SetDefaultLanguage("en-US");
// // Set up a SpellcheckWordIterator object which extracts English words,
// // and retrieve them.
// SpellcheckWordIterator iterator;
// string16 text(UTF8ToUTF16("this is a test."));
// iterator.Initialize(&attribute, text.c_str(), text_.length(), true);
// string16 word;
// int offset;
// int length;
// while (iterator.GetNextWord(&word, &offset, &length)) {
// ...
// }
class SpellcheckWordIterator {
// Initializes a word-iterator object with the language-specific attribute and
// a multi-language text (it does not have to be NULL-terminated). If we need
// to split contractions and concatenated words, call this function with its
// 'allow_contraction' parameter false.
bool Initialize(const SpellcheckCharAttribute* attribute,
const char16* word,
size_t length,
bool allow_contraction);
// Retrieves a word (or a contraction), stores its copy to 'word_string', and
// stores the position and the length for input word to 'word_start'. Since
// this function normalizes the output word, the length of 'word_string' may
// be different from the 'word_length'. Therefore, when we call functions that
// changes the input text, such as string16::replace(), we need to use
// 'word_start' and 'word_length' as listed in the following snippet.
// while(iterator.GetNextWord(&word, &offset, &length))
// text.replace(offset, length, word);
bool GetNextWord(string16* word_string,
int* word_start,
int* word_length);
// Releases all the resources attached to this object.
void Close();
// Normalizes a non-terminated string returned from an ICU word-break
// iterator. A word returned from an ICU break iterator may include characters
// not supported by our spellchecker, e.g. ligatures, combining/ characters,
// full-width letters, etc. This function replaces such characters with
// alternative characters supported by our spellchecker. This function also
// calls SpellcheckWordIterator::OutputChar() to filter out false-positive
// characters.
bool Normalize(int input_start,
int input_length,
string16* output_string) const;
// The pointer to the input string from which we are extracting words.
const char16* word_;
// The length of the original string.
int length_;
// The current position in the original string.
int position_;
// The language-specific attributes used for filtering out non-word
// characters.
const SpellcheckCharAttribute* attribute_;
// The ICU break iterator.
UBreakIterator* iterator_;