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