| // Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| part of intl; |
| |
| /// Bidi stands for Bi-directional text. According to |
| /// [Wikipedia](http://en.wikipedia.org/wiki/Bi-directional_text): |
| /// Bi-directional text is text containing text in both text directionalities, |
| /// both right-to-left (RTL) and left-to-right (LTR). It generally involves text |
| /// containing different types of alphabets, but may also refer to |
| /// boustrophedon, which is changing text directionality in each row. |
| /// |
| /// Utility class for formatting display text in a potentially |
| /// opposite-directionality context without garbling layout issues. Mostly a |
| /// very "slimmed-down" and dart-ified port of the Closure Birectional |
| /// formatting libary. If there is a utility in the Closure library (or ICU, or |
| /// elsewhere) that you would like this formatter to make available, please |
| /// contact the Dart team. |
| /// |
| /// Provides the following functionality: |
| /// |
| /// 1. *BiDi Wrapping* |
| /// When text in one language is mixed into a document in another, opposite- |
| /// directionality language, e.g. when an English business name is embedded in a |
| /// Hebrew web page, both the inserted string and the text following it may be |
| /// displayed incorrectly unless the inserted string is explicitly separated |
| /// from the surrounding text in a "wrapper" that declares its directionality at |
| /// the start and then resets it back at the end. This wrapping can be done in |
| /// HTML mark-up (e.g. a 'span dir=rtl' tag) or - only in contexts where mark-up |
| /// can not be used - in Unicode BiDi formatting codes (LRE|RLE and PDF). |
| /// Providing such wrapping services is the basic purpose of the BiDi formatter. |
| /// |
| /// 2. *Directionality estimation* |
| /// How does one know whether a string about to be inserted into surrounding |
| /// text has the same directionality? Well, in many cases, one knows that this |
| /// must be the case when writing the code doing the insertion, e.g. when a |
| /// localized message is inserted into a localized page. In such cases there is |
| /// no need to involve the BiDi formatter at all. In the remaining cases, e.g. |
| /// when the string is user-entered or comes from a database, the language of |
| /// the string (and thus its directionality) is not known a priori, and must be |
| /// estimated at run-time. The BiDi formatter does this automatically. |
| /// |
| /// 3. *Escaping* |
| /// When wrapping plain text - i.e. text that is not already HTML or HTML- |
| /// escaped - in HTML mark-up, the text must first be HTML-escaped to prevent |
| /// XSS attacks and other nasty business. This of course is always true, but the |
| /// escaping cannot be done after the string has already been wrapped in |
| /// mark-up, so the BiDi formatter also serves as a last chance and includes |
| /// escaping services. |
| /// |
| /// Thus, in a single call, the formatter will escape the input string as |
| /// specified, determine its directionality, and wrap it as necessary. It is |
| /// then up to the caller to insert the return value in the output. |
| |
| class BidiFormatter { |
| |
| /// The direction of the surrounding text (the context). |
| TextDirection contextDirection; |
| |
| /// Indicates if we should always wrap the formatted text in a <span<,. |
| bool _alwaysSpan; |
| |
| /// Create a formatting object with a direction. If [alwaysSpan] is true we |
| /// should always use a `span` tag, even when the input directionality is |
| /// neutral or matches the context, so that the DOM structure of the output |
| /// does not depend on the combination of directionalities. |
| BidiFormatter.LTR([alwaysSpan = false]) |
| : contextDirection = TextDirection.LTR, |
| _alwaysSpan = alwaysSpan; |
| BidiFormatter.RTL([alwaysSpan = false]) |
| : contextDirection = TextDirection.RTL, |
| _alwaysSpan = alwaysSpan; |
| BidiFormatter.UNKNOWN([alwaysSpan = false]) |
| : contextDirection = TextDirection.UNKNOWN, |
| _alwaysSpan = alwaysSpan; |
| |
| /// Is true if the known context direction for this formatter is RTL. |
| bool get isRTL => contextDirection == TextDirection.RTL; |
| |
| /// Formats a string of a given (or estimated, if not provided) [direction] |
| /// for use in HTML output of the context directionality, so an |
| /// opposite-directionality string is neither garbled nor garbles what follows |
| /// it. |
| /// |
| ///If the input string's directionality doesn't match the context |
| /// directionality, we wrap it with a `span` tag and add a `dir` attribute |
| /// (either "dir=rtl" or "dir=ltr"). If alwaysSpan was true when constructing |
| /// the formatter, the input is always wrapped with `span` tag, skipping the |
| /// dir attribute when it's not needed. |
| /// |
| /// If [resetDir] is true and the overall directionality or the exit |
| /// directionality of [text] is opposite to the context directionality, |
| /// a trailing unicode BiDi mark matching the context directionality is |
| /// appended (LRM or RLM). If [isHtml] is false, we HTML-escape the [text]. |
| String wrapWithSpan(String text, |
| {bool isHtml: false, bool resetDir: true, TextDirection direction}) { |
| if (direction == null) direction = estimateDirection(text, isHtml: isHtml); |
| var result; |
| if (!isHtml) text = HTML_ESCAPE.convert(text); |
| var directionChange = contextDirection.isDirectionChange(direction); |
| if (_alwaysSpan || directionChange) { |
| var spanDirection = ''; |
| if (directionChange) { |
| spanDirection = ' dir=${direction.spanText}'; |
| } |
| result = '<span$spanDirection>$text</span>'; |
| } else { |
| result = text; |
| } |
| return result + (resetDir ? _resetDir(text, direction, isHtml) : ''); |
| } |
| |
| /// Format [text] of a known (if specified) or estimated [direction] for use |
| /// in *plain-text* output of the context directionality, so an |
| /// opposite-directionality text is neither garbled nor garbles what follows |
| /// it. Unlike wrapWithSpan, this makes use of unicode BiDi formatting |
| /// characters instead of spans for wrapping. The returned string would be |
| /// RLE+text+PDF for RTL text, or LRE+text+PDF for LTR text. |
| /// |
| /// If [resetDir] is true, and if the overall directionality or the exit |
| /// directionality of text are opposite to the context directionality, |
| /// a trailing unicode BiDi mark matching the context directionality is |
| /// appended (LRM or RLM). |
| /// |
| /// In HTML, the *only* valid use of this function is inside of elements that |
| /// do not allow markup, e.g. an 'option' tag. |
| /// This function does *not* do HTML-escaping regardless of the value of |
| /// [isHtml]. [isHtml] is used to designate if the text contains HTML (escaped |
| /// or unescaped). |
| String wrapWithUnicode(String text, |
| {bool isHtml: false, bool resetDir: true, TextDirection direction}) { |
| if (direction == null) direction = estimateDirection(text, isHtml: isHtml); |
| var result = text; |
| if (contextDirection.isDirectionChange(direction)) { |
| var marker = direction == TextDirection.RTL ? Bidi.RLE : Bidi.LRE; |
| result = "${marker}$text${Bidi.PDF}"; |
| } |
| return result + (resetDir ? _resetDir(text, direction, isHtml) : ''); |
| } |
| |
| /// Estimates the directionality of [text] using the best known |
| /// general-purpose method (using relative word counts). A |
| /// TextDirection.UNKNOWN return value indicates completely neutral input. |
| /// [isHtml] is true if [text] HTML or HTML-escaped. |
| TextDirection estimateDirection(String text, {bool isHtml: false}) { |
| return Bidi.estimateDirectionOfText(text, isHtml: isHtml); //TODO~!!! |
| } |
| |
| /// Returns a unicode BiDi mark matching the surrounding context's [direction] |
| /// (not necessarily the direction of [text]). The function returns an LRM or |
| /// RLM if the overall directionality or the exit directionality of [text] is |
| /// opposite the context directionality. Otherwise |
| /// return the empty string. [isHtml] is true if [text] is HTML or |
| /// HTML-escaped. |
| String _resetDir(String text, TextDirection direction, bool isHtml) { |
| // endsWithRtl and endsWithLtr are called only if needed (short-circuit). |
| if ((contextDirection == TextDirection.LTR && |
| (direction == TextDirection.RTL || |
| Bidi.endsWithRtl(text, isHtml))) || |
| (contextDirection == TextDirection.RTL && |
| (direction == TextDirection.LTR || |
| Bidi.endsWithLtr(text, isHtml)))) { |
| return contextDirection == TextDirection.LTR ? Bidi.LRM : Bidi.RLM; |
| } else { |
| return ''; |
| } |
| } |
| } |