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intl/lib/src/intl/bidi_utils.dart

Index: intl/lib/src/intl/bidi_utils.dart
diff --git a/intl/lib/src/intl/bidi_utils.dart b/intl/lib/src/intl/bidi_utils.dart
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-// 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 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.
- *
- * This file provides some utility classes for determining directionality of
- * text, switching CSS layout from LTR to RTL, and other normalizing utilities
- * needed when switching between RTL and LTR formatting.
- *
- * It defines the TextDirection class which is used to represent directionality
- * of text,
- * In most cases, it is preferable to use bidi_formatter.dart, which provides
- * bidi functionality in the given directional context, instead of using
- * bidi_utils.dart directly.
- */
-class TextDirection {
-  static const LTR = const TextDirection._('LTR', 'ltr');
-  static const RTL = const TextDirection._('RTL', 'rtl');
-  // If the directionality of the text cannot be determined and we are not using
-  // the context direction (or if the context direction is unknown), then the
-  // text falls back on the more common ltr direction.
-  static const UNKNOWN = const TextDirection._('UNKNOWN', 'ltr');
-
-  /**
-   * Textual representation of the directionality constant. One of
-   * 'LTR', 'RTL', or 'UNKNOWN'.
-   */
-  final String value;
-
-  /** Textual representation of the directionality when used in span tag. */
-  final String spanText;
-
-  const TextDirection._(this.value, this.spanText);
-
-  /**
-   * Returns true if [otherDirection] is known to be different from this
-   * direction.
-   */
-  bool isDirectionChange(TextDirection otherDirection) =>
-      otherDirection != TextDirection.UNKNOWN && this != otherDirection;
-}
-
-/**
- * This provides utility methods for working with bidirectional text. All
- * of the methods are static, and are organized into a class primarily to
- * group them together for documentation and discoverability.
- */
-class Bidi {
-
-  /** Unicode "Left-To-Right Embedding" (LRE) character. */
-  static const LRE = '\u202A';
-
-  /** Unicode "Right-To-Left Embedding" (RLE) character. */
-  static const RLE = '\u202B';
-
-  /** Unicode "Pop Directional Formatting" (PDF) character. */
-  static const PDF = '\u202C';
-
-  /** Unicode "Left-To-Right Mark" (LRM) character. */
-  static const LRM = '\u200E';
-
-  /** Unicode "Right-To-Left Mark" (RLM) character. */
-  static const RLM = '\u200F';
-
-  /** Constant to define the threshold of RTL directionality. */
-  static num _RTL_DETECTION_THRESHOLD = 0.40;
-
-  /**
-   * Practical patterns to identify strong LTR and RTL characters, respectively.
-   * These patterns are not completely correct according to the Unicode
-   * standard. They are simplified for performance and small code size.
-   */
-  static const String _LTR_CHARS =
-      r'A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590'
-      r'\u0800-\u1FFF\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF';
-  static const String _RTL_CHARS = r'\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC';
-
-  /**
-   * Returns the input [text] with spaces instead of HTML tags or HTML escapes,
-   * which is helpful for text directionality estimation.
-   * Note: This function should not be used in other contexts.
-   * It does not deal well with many things: comments, script,
-   * elements, style elements, dir attribute,`>` in quoted attribute values,
-   * etc. But it does handle well enough the most common use cases.
-   * Since the worst that can happen as a result of these shortcomings is that
-   * the wrong directionality will be estimated, we have not invested in
-   * improving this.
-   */
-  static String stripHtmlIfNeeded(String text) {
-    // The regular expression is simplified for an HTML tag (opening or
-    // closing) or an HTML escape. We might want to skip over such expressions
-    // when estimating the text directionality.
-    return text.replaceAll(new RegExp(r'<[^>]*>|&[^;]+;'), ' ');
-  }
-
-  /**
-   * Determines if the first character in [text] with strong directionality is
-   * LTR. If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool startsWithLtr(String text, [isHtml = false]) {
-    return new RegExp('^[^$_RTL_CHARS]*[$_LTR_CHARS]')
-        .hasMatch(isHtml ? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the first character in [text] with strong directionality is
-   * RTL. If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool startsWithRtl(String text, [isHtml = false]) {
-    return new RegExp('^[^$_LTR_CHARS]*[$_RTL_CHARS]')
-        .hasMatch(isHtml ? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the exit directionality (ie, the last strongly-directional
-   * character in [text] is LTR. If [isHtml] is true, the text is HTML or
-   * HTML-escaped.
-   */
-  static bool endsWithLtr(String text, [isHtml = false]) {
-    return new RegExp('[$_LTR_CHARS][^$_RTL_CHARS]*\$')
-        .hasMatch(isHtml ? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the exit directionality (ie, the last strongly-directional
-   * character in [text] is RTL. If [isHtml] is true, the text is HTML or
-   * HTML-escaped.
-   */
-  static bool endsWithRtl(String text, [isHtml = false]) {
-    return new RegExp('[$_RTL_CHARS][^$_LTR_CHARS]*\$')
-        .hasMatch(isHtml ? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the given [text] has any LTR characters in it.
-   * If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool hasAnyLtr(String text, [isHtml = false]) {
-    return new RegExp(r'[' '$_LTR_CHARS' r']')
-        .hasMatch(isHtml ? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Determines if the given [text] has any RTL characters in it.
-   * If [isHtml] is true, the text is HTML or HTML-escaped.
-   */
-  static bool hasAnyRtl(String text, [isHtml = false]) {
-    return new RegExp(r'[' '$_RTL_CHARS' r']')
-        .hasMatch(isHtml ? stripHtmlIfNeeded(text) : text);
-  }
-
-  /**
-   * Check if a BCP 47 / III [languageString] indicates an RTL language.
-   *
-   * i.e. either:
-   * - a language code explicitly specifying one of the right-to-left scripts,
-   *   e.g. "az-Arab", or
-   * - a language code specifying one of the languages normally written in a
-   *   right-to-left script, e.g. "fa" (Farsi), except ones explicitly
-   *   specifying Latin or Cyrillic script (which are the usual LTR
-   *   alternatives).
-   *
-   * The list of right-to-left scripts appears in the 100-199 range in
-   * http://www.unicode.org/iso15924/iso15924-num.html, of which Arabic and
-   * Hebrew are by far the most widely used. We also recognize Thaana, N'Ko, and
-   * Tifinagh, which also have significant modern usage. The rest (Syriac,
-   * Samaritan, Mandaic, etc.) seem to have extremely limited or no modern usage
-   * and are not recognized.
-   * The languages usually written in a right-to-left script are taken as those
-   * with Suppress-Script: Hebr|Arab|Thaa|Nkoo|Tfng  in
-   * http://www.iana.org/assignments/language-subtag-registry,
-   * as well as Sindhi (sd) and Uyghur (ug).
-   * The presence of other subtags of the language code, e.g. regions like EG
-   * (Egypt), is ignored.
-   */
-  static bool isRtlLanguage(String languageString) {
-    return new RegExp(r'^(ar|dv|he|iw|fa|nqo|ps|sd|ug|ur|yi|.*[-_]'
-        r'(Arab|Hebr|Thaa|Nkoo|Tfng))(?!.*[-_](Latn|Cyrl)($|-|_))'
-        r'($|-|_)', caseSensitive: false).hasMatch(languageString);
-  }
-
-  /**
-   * Enforce the [html] snippet in RTL directionality regardless of overall
-   * context. If the html piece was enclosed by a tag, the direction will be
-   * applied to existing tag, otherwise a span tag will be added as wrapper.
-   * For this reason, if html snippet start with with tag, this tag must enclose
-   * the whole piece. If the tag already has a direction specified, this new one
-   * will override existing one in behavior (should work on Chrome, FF, and IE
-   * since this was ported directly from the Closure version).
-   */
-  static String enforceRtlInHtml(String html) =>
-      _enforceInHtmlHelper(html, 'rtl');
-
-  /**
-   * Enforce RTL on both end of the given [text] using unicode BiDi formatting
-   * characters RLE and PDF.
-   */
-  static String enforceRtlInText(String text) => '$RLE$text$PDF';
-
-  /**
-   * Enforce the [html] snippet in LTR directionality regardless of overall
-   * context. If the html piece was enclosed by a tag, the direction will be
-   * applied to existing tag, otherwise a span tag will be added as wrapper.
-   * For this reason, if html snippet start with with tag, this tag must enclose
-   * the whole piece. If the tag already has a direction specified, this new one
-   * will override existing one in behavior (tested on FF and IE).
-   */
-  static String enforceLtrInHtml(String html) =>
-      _enforceInHtmlHelper(html, 'ltr');
-
-  /**
-   * Enforce LTR on both end of the given [text] using unicode BiDi formatting
-   * characters LRE and PDF.
-   */
-  static String enforceLtrInText(String text) => '$LRE$text$PDF';
-
-  /**
-   * Enforce the [html] snippet in the desired [direction] regardless of overall
-   * context. If the html piece was enclosed by a tag, the direction will be
-   * applied to existing tag, otherwise a span tag will be added as wrapper.
-   * For this reason, if html snippet start with with tag, this tag must enclose
-   * the whole piece. If the tag already has a direction specified, this new one
-   * will override existing one in behavior (tested on FF and IE).
-   */
-  static String _enforceInHtmlHelper(String html, String direction) {
-    if (html.startsWith('<')) {
-      StringBuffer buffer = new StringBuffer();
-      var startIndex = 0;
-      Match match = new RegExp('<\\w+').firstMatch(html);
-      if (match != null) {
-        buffer
-          ..write(html.substring(startIndex, match.end))
-          ..write(' dir=$direction');
-        startIndex = match.end;
-      }
-      return (buffer..write(html.substring(startIndex))).toString();
-    }
-    // '\n' is important for FF so that it won't incorrectly merge span groups.
-    return '\n<span dir=$direction>$html</span>';
-  }
-
-  /**
-   * Apply bracket guard to [str] using html span tag. This is to address the
-   * problem of messy bracket display that frequently happens in RTL layout.
-   * If [isRtlContext] is true, then we explicitly want to wrap in a span of RTL
-   * directionality, regardless of the estimated directionality.
-   */
-  static String guardBracketInHtml(String str, [bool isRtlContext]) {
-    var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
-    RegExp matchingBrackets =
-        new RegExp(r'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(&lt;.*?(&gt;)+)');
-    return _guardBracketHelper(str, matchingBrackets,
-        '<span dir=${useRtl? "rtl" : "ltr"}>', '</span>');
-  }
-
-  /**
-   * Apply bracket guard to [str] using LRM and RLM. This is to address the
-   * problem of messy bracket display that frequently happens in RTL layout.
-   * This version works for both plain text and html, but in some cases is not
-   * as good as guardBracketInHtml.
-   * If [isRtlContext] is true, then we explicitly want to wrap in a span of RTL
-   * directionality, regardless of the estimated directionality.
-   */
-  static String guardBracketInText(String str, [bool isRtlContext]) {
-    var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
-    var mark = useRtl ? RLM : LRM;
-    return _guardBracketHelper(str,
-        new RegExp(r'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(<.*?>+)'), mark, mark);
-  }
-
-  /**
-   * (Mostly) reimplements the $& functionality of "replace" in JavaScript.
-   * Given a [str] and the [regexp] to match with, optionally supply a string to
-   * be inserted [before] the match and/or [after]. For example,
-   * `_guardBracketHelper('firetruck', new RegExp('truck'), 'hydrant', '!')`
-   * would return 'firehydrant!'.
-   */
-  // TODO(efortuna): Get rid of this once this is implemented in Dart.
-  // See Issue 2979.
-  static String _guardBracketHelper(String str, RegExp regexp,
-      [String before, String after]) {
-    var buffer = new StringBuffer();
-    var startIndex = 0;
-    regexp.allMatches(str).forEach((match) {
-      buffer
-        ..write(str.substring(startIndex, match.start))
-        ..write(before)
-        ..write(str.substring(match.start, match.end))
-        ..write(after);
-      startIndex = match.end;
-    });
-    return (buffer..write(str.substring(startIndex))).toString();
-  }
-
-  /**
-   * 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.
-   *
-   * If the number of RTL words is above a certain percentage of the total
-   * number of strongly directional words, returns RTL.
-   * Otherwise, if any words are strongly or weakly LTR, returns LTR.
-   * Otherwise, returns UNKNOWN, which is used to mean `neutral`.
-   * Numbers and URLs are counted as weakly LTR.
-   */
-  static TextDirection estimateDirectionOfText(String text,
-      {bool isHtml: false}) {
-    text = isHtml ? stripHtmlIfNeeded(text) : text;
-    var rtlCount = 0;
-    var total = 0;
-    var hasWeaklyLtr = false;
-    // Split a string into 'words' for directionality estimation based on
-    // relative word counts.
-    for (String token in text.split(new RegExp(r'\s+'))) {
-      if (startsWithRtl(token)) {
-        rtlCount++;
-        total++;
-      } else if (new RegExp(r'^http://').hasMatch(token)) {
-        // Checked if token looks like something that must always be LTR even in
-        // RTL text, such as a URL.
-        hasWeaklyLtr = true;
-      } else if (hasAnyLtr(token)) {
-        total++;
-      } else if (new RegExp(r'\d').hasMatch(token)) {
-        // Checked if token contains any numerals.
-        hasWeaklyLtr = true;
-      }
-    }
-
-    if (total == 0) {
-      return hasWeaklyLtr ? TextDirection.LTR : TextDirection.UNKNOWN;
-    } else if (rtlCount > _RTL_DETECTION_THRESHOLD * total) {
-      return TextDirection.RTL;
-    } else {
-      return TextDirection.LTR;
-    }
-  }
-
-  /**
-   * Replace the double and single quote directly after a Hebrew character in
-   * [str] with GERESH and GERSHAYIM. This is most likely the user's intention.
-   */
-  static String normalizeHebrewQuote(String str) {
-    StringBuffer buf = new StringBuffer();
-    if (str.length > 0) {
-      buf.write(str.substring(0, 1));
-    }
-    // Start at 1 because we're looking for the patterns [\u0591-\u05f2])" or
-    // [\u0591-\u05f2]'.
-    for (int i = 1; i < str.length; i++) {
-      if (str.substring(i, i + 1) == '"' &&
-          new RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i - 1, i))) {
-        buf.write('\u05f4');
-      } else if (str.substring(i, i + 1) == "'" &&
-          new RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i - 1, i))) {
-        buf.write('\u05f3');
-      } else {
-        buf.write(str.substring(i, i + 1));
-      }
-    }
-    return buf.toString();
-  }
-
-  /**
-   * Check the estimated directionality of [str], return true if the piece of
-   * text should be laid out in RTL direction. If [isHtml] is true, the string
-   * is HTML or HTML-escaped.
-   */
-  static bool detectRtlDirectionality(String str, {bool isHtml: false}) =>
-      estimateDirectionOfText(str, isHtml: isHtml) == TextDirection.RTL;
-}