112 lines
2.8 KiB
Plaintext
112 lines
2.8 KiB
Plaintext
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/**
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* Copyright (c) 2013-present, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*
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* @providesModule UnicodeBidiDirection
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* @typechecks
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* @flow
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*/
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/**
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* Constants to represent text directionality
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*
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* Also defines a *global* direciton, to be used in bidi algorithms as a
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* default fallback direciton, when no better direction is found or provided.
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*
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* NOTE: Use `setGlobalDir()`, or update `initGlobalDir()`, to set the initial
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* global direction value based on the application.
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*
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* Part of the 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 invariant = require('./invariant');
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export type BidiDirection = 'LTR' | 'RTL' | 'NEUTRAL';
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export type HTMLDir = 'ltr' | 'rtl';
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const NEUTRAL = 'NEUTRAL'; // No strong direction
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const LTR = 'LTR'; // Left-to-Right direction
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const RTL = 'RTL'; // Right-to-Left direction
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let globalDir: ?BidiDirection = null;
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// == Helpers ==
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/**
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* Check if a directionality value is a Strong one
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*/
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function isStrong(dir: BidiDirection): boolean {
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return dir === LTR || dir === RTL;
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}
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/**
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* Get string value to be used for `dir` HTML attribute or `direction` CSS
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* property.
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*/
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function getHTMLDir(dir: BidiDirection): HTMLDir {
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invariant(isStrong(dir), '`dir` must be a strong direction to be converted to HTML Direction');
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return dir === LTR ? 'ltr' : 'rtl';
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}
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/**
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* Get string value to be used for `dir` HTML attribute or `direction` CSS
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* property, but returns null if `dir` has same value as `otherDir`.
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* `null`.
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*/
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function getHTMLDirIfDifferent(dir: BidiDirection, otherDir: BidiDirection): ?HTMLDir {
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invariant(isStrong(dir), '`dir` must be a strong direction to be converted to HTML Direction');
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invariant(isStrong(otherDir), '`otherDir` must be a strong direction to be converted to HTML Direction');
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return dir === otherDir ? null : getHTMLDir(dir);
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}
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// == Global Direction ==
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/**
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* Set the global direction.
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*/
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function setGlobalDir(dir: BidiDirection): void {
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globalDir = dir;
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}
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/**
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* Initialize the global direction
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*/
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function initGlobalDir(): void {
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setGlobalDir(LTR);
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}
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/**
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* Get the global direction
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*/
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function getGlobalDir(): BidiDirection {
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if (!globalDir) {
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this.initGlobalDir();
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}
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invariant(globalDir, 'Global direction not set.');
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return globalDir;
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}
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const UnicodeBidiDirection = {
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// Values
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NEUTRAL,
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LTR,
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RTL,
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// Helpers
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isStrong,
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getHTMLDir,
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getHTMLDirIfDifferent,
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// Global Direction
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setGlobalDir,
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initGlobalDir,
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getGlobalDir
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};
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module.exports = UnicodeBidiDirection;
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