Start moving non-platform libraries from lib/ to pkg/ .

lib/i18n/bidi_utils.dart

-// 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.
-
-/**
- * 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 final LTR = const TextDirection._('LTR', 'ltr');
-  static final 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 final 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) {
-    return otherDirection != TextDirection.UNKNOWN && this != otherDirection;
-  }
-}
-
-/** Unicode "Left-To-Right Embedding" (LRE) character. */
-final LRE = '\u202A';
-
-/** Unicode "Right-To-Left Embedding" (RLE) character. */
-final RLE = '\u202B';
-
-/** Unicode "Pop Directional Formatting" (PDF) character. */
-final PDF = '\u202C';
-
-/** Unicode "Left-To-Right Mark" (LRM) character. */
-final LRM = '\u200E';
-
-/** Unicode "Right-To-Left Mark" (RLM) character. */
-final RLM = '\u200F';
-
-/** Constant to define the threshold of RTL directionality. */
-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.
- */
-final String _LTR_CHARS =
-    @'A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590'
-    @'\u0800-\u1FFF\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF';
-final String _RTL_CHARS = @'\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.
- */
-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(const RegExp(@'<[^>]*>|&[^;]+;'), ' ');
-}
-
-/**
- * Determines if the first character in [text] with strong directionality is
- * LTR. If [isHtml] is true, the text is HTML or HTML-escaped.
- */
-bool startsWithLtr(String text, [isHtml=false]) {
-  return const 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.
- */
-bool startsWithRtl(String text, [isHtml=false]) {
-  return const 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.
- */
-bool endsWithLtr(String text, [isHtml=false]) {
-  return const 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.
- */
-bool endsWithRtl(String text, [isHtml=false]) {
-  return const 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.
- */
-bool hasAnyLtr(String text, [isHtml=false]) {
-  return const RegExp(@'[' '$_LTR_CHARS' @']').hasMatch(
-      isHtml? stripHtmlIfNeeded(text) : text);
-}
-
-/**
- * Determines if the given [text] has any RTL characters in it.
- * If [isHtml] is true, the text is HTML or HTML-escaped.
- */
-bool hasAnyRtl(String text, [isHtml=false]) {
-  return const RegExp(@'[' '$_RTL_CHARS' @']').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.
- */
-bool isRtlLanguage(String languageString) {
-  return const RegExp(@'^(ar|dv|he|iw|fa|nqo|ps|sd|ug|ur|yi|.*[-_]'
-      @'(Arab|Hebr|Thaa|Nkoo|Tfng))(?!.*[-_](Latn|Cyrl)($|-|_))'
-      @'($|-|_)', ignoreCase : true).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).
- */
-String enforceRtlInHtml(String html) {
-  return _enforceInHtmlHelper(html, 'rtl');
-}
-
-/**
- * Enforce RTL on both end of the given [text] using unicode BiDi formatting
- * characters RLE and PDF.
- */
-String enforceRtlInText(String text) {
-  return '$RLE$text$PDF';
-}
-
-/**
- * Enforce the [html] snippet in LTR directionality regardless of overall
- * context. If the html piece was enclosed by a tag, the direction will be 
- * applied to existing tag, otherwise a span tag will be added as wrapper.
- * For this reason, if html snippet start with with tag, this tag must enclose
- * the whole piece. If the tag already has a direction specified, this new one
- * will override existing one in behavior (tested on FF and IE).
- */
-String enforceLtrInHtml(String html) {
-  return _enforceInHtmlHelper(html, 'ltr');
-}
-
-/**
- * Enforce LTR on both end of the given [text] using unicode BiDi formatting
- * characters LRE and PDF.
- */
-String enforceLtrInText(String text) {
-  return '$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).
- */
-String _enforceInHtmlHelper(String html, String direction) {
-  if (html.startsWith('<')) {
-    StringBuffer buffer = new StringBuffer();
-    var startIndex = 0;
-    Match match = const RegExp('<\\w+').firstMatch(html);
-    if (match != null) {
-      buffer.add(html.substring(
-          startIndex, match.end())).add(' dir=$direction');
-      startIndex = match.end();
-    }
-    return buffer.add(html.substring(startIndex)).toString();
-  }
-  // '\n' is important for FF so that it won't incorrectly merge span groups.
-  return '\n<span dir=$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.
- */
-String guardBracketInHtml(String str, [bool isRtlContext]) {
-  var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
-  RegExp matchingBrackets = 
-      const RegExp(@'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(&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.
- */
-String guardBracketInText(String str, [bool isRtlContext]) {
-  var useRtl = isRtlContext == null ? hasAnyRtl(str) : isRtlContext;
-  var mark = useRtl ? RLM : LRM;
-  return _guardBracketHelper(str,
-      const RegExp(@'(\(.*?\)+)|(\[.*?\]+)|(\{.*?\}+)|(<.*?>+)'), 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', const RegExp('truck'), 'hydrant', '!')`
- * would return 'firehydrant!'.
- */
-// TODO(efortuna): Get rid of this once this is implemented in Dart.
-// See Issue 2979.
-String _guardBracketHelper(String str, RegExp regexp, [String before,
-    String after]) {
-  StringBuffer buffer = new StringBuffer();
-  var startIndex = 0;
-  Iterable matches = regexp.allMatches(str);
-  for (Match match in matches) {
-    buffer.add(str.substring(startIndex, match.start())).add(before);
-    buffer.add(str.substring(match.start(), match.end())).add(after);
-    startIndex = match.end();
-  }
-  return buffer.add(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.
- */
-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(const RegExp(@'\s+'))) {
-    if (startsWithRtl(token)) {
-      rtlCount++;
-      total++;
-    } else if (const RegExp(@'^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 (const RegExp(@'\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;
-  }
-}
-
-/**
- * Find the first index in [str] of the first closing parenthesis that does
- * not match an opening parenthesis.
- */
-int _unmatchedParenIndex(String str) {
-  int sum = 0;
-  int index = 0;
-  while (sum >= 0 || index > str.length) {
-    int char = str.charCodeAt(index);
-    if (char == '('.charCodeAt(0)) sum++;
-    else if (char == ')'.charCodeAt(0)) sum--;
-    index++;
-  }
-  return index;
-}
-
-/**
- * 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.
- */
-String normalizeHebrewQuote(String str) {
-  StringBuffer buf = new StringBuffer();
-  if (str.length > 0) {
-    buf.add(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) == '"'
-        && const RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i-1, i))) {
-      buf.add('\u05f4');
-    } else if (str.substring(i, i+1) == "'"
-        && const RegExp('[\u0591-\u05f2]').hasMatch(str.substring(i-1, i))) {
-      buf.add('\u05f3');
-    } else {
-      buf.add(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.
- */
-bool detectRtlDirectionality(String str, [bool isHtml]) {
-  return estimateDirectionOfText(str, isHtml) == TextDirection.RTL;
-}