95 lines
2.4 KiB
Plaintext
95 lines
2.4 KiB
Plaintext
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/**
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* Copyright (c) 2013-present, Facebook, Inc.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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* @providesModule UnicodeBidiService
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* @typechecks
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* @flow
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*/
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/**
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* Stateful API for text direction detection
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*
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* This class can be used in applications where you need to detect the
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* direction of a sequence of text blocks, where each direction shall be used
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* as the fallback direction for the next one.
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*
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* NOTE: A default direction, if not provided, is set based on the global
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* direction, as defined by `UnicodeBidiDirection`.
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*
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* == Example ==
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* ```
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* var UnicodeBidiService = require('UnicodeBidiService');
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*
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* var bidiService = new UnicodeBidiService();
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*
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* ...
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*
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* bidiService.reset();
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* for (var para in paragraphs) {
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* var dir = bidiService.getDirection(para);
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* ...
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* }
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* ```
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*
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* Part of our implementation of Unicode Bidirectional Algorithm (UBA)
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* Unicode Standard Annex #9 (UAX9)
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* http://www.unicode.org/reports/tr9/
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*/
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'use strict';
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const UnicodeBidi = require('./UnicodeBidi');
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const UnicodeBidiDirection = require('./UnicodeBidiDirection');
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const invariant = require('./invariant');
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import type { BidiDirection } from './UnicodeBidiDirection';
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class UnicodeBidiService {
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_defaultDir: BidiDirection;
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_lastDir: BidiDirection;
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/**
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* Stateful class for paragraph direction detection
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*
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* @param defaultDir Default direction of the service
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*/
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constructor(defaultDir: ?BidiDirection) {
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if (!defaultDir) {
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defaultDir = UnicodeBidiDirection.getGlobalDir();
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} else {
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invariant(UnicodeBidiDirection.isStrong(defaultDir), 'Default direction must be a strong direction (LTR or RTL)');
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}
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this._defaultDir = defaultDir;
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this.reset();
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}
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/**
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* Reset the internal state
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*
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* Instead of creating a new instance, you can just reset() your instance
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* everytime you start a new loop.
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*/
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reset(): void {
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this._lastDir = this._defaultDir;
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}
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/**
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* Returns the direction of a block of text, and remembers it as the
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* fall-back direction for the next paragraph.
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*
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* @param str A text block, e.g. paragraph, table cell, tag
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* @return The resolved direction
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*/
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getDirection(str: string): BidiDirection {
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this._lastDir = UnicodeBidi.getDirection(str, this._lastDir);
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return this._lastDir;
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}
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}
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module.exports = UnicodeBidiService;
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