lib/src/util.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.

import 'dart:convert';

import 'assets/case_folding.dart';
import 'assets/html_entities.dart';
import 'charcode.dart';
import 'patterns.dart';

/// One or more whitespace, for compressing.
final _oneOrMoreWhitespacePattern = RegExp('[ \n\r\t]+');

/// Escapes (`'`), (`"`), (`<`), (`>`) and (`&`) characters.
String escapeHtml(String html) => const HtmlEscape(HtmlEscapeMode(
      escapeApos: true,
      escapeLtGt: true,
      escapeQuot: true,
    )).convert(html);

/// Escapes (`"`), (`<`) and (`>`) characters.
String escapeHtmlAttribute(String text) =>
    const HtmlEscape(HtmlEscapeMode.attribute).convert(text);

/// "Normalizes" a link label, according to the [CommonMark spec].
///
/// [CommonMark spec] https://spec.commonmark.org/0.30/#link-label
String normalizeLinkLabel(String label) {
  var text = label.trim().replaceAll(_oneOrMoreWhitespacePattern, ' ');
  for (var i = 0; i < text.length; i++) {
    final mapped = caseFoldingMap[text[i]];
    if (mapped != null) {
      text = text.replaceRange(i, i + 1, mapped);
    }
  }
  return text;
}

/// Normalizes a link destination, including the process of HTML characters
/// decoding  and percent encoding.
// See the description of these examples:
// https://spec.commonmark.org/0.30/#example-501
// https://spec.commonmark.org/0.30/#example-502
String normalizeLinkDestination(String destination) {
  // Decode first, because the destination might have been partly encoded.
  // For example https://spec.commonmark.org/0.30/#example-502.
  // With this function, `foo%20b&auml;` will be parsed in the following steps:
  // 1. foo b&auml;
  // 2. foo bä
  // 3. foo%20b%C3%A4
  try {
    destination = Uri.decodeFull(destination);
  } catch (_) {}
  return Uri.encodeFull(decodeHtmlCharacters(destination));
}

/// Normalizes a link title, including the process of HTML characters decoding
/// and HTML characters escaping.
// See the description of these examples:
// https://spec.commonmark.org/0.30/#example-505
// https://spec.commonmark.org/0.30/#example-506
// https://spec.commonmark.org/0.30/#example-507
// https://spec.commonmark.org/0.30/#example-508
String normalizeLinkTitle(String title) =>
    escapeHtmlAttribute(decodeHtmlCharacters(title));

///  Decodes HTML entity and numeric character references, for example decode
/// `&#35` to `#`.
String decodeHtmlCharacters(String input) =>
    input.replaceAllMapped(htmlCharactersPattern, decodeHtmlCharacterFromMatch);

/// Decodes HTML entity and numeric character references from the given [match].
String decodeHtmlCharacterFromMatch(Match match) {
  final text = match.match;
  final entity = match[1];
  final decimalNumber = match[2];
  final hexadecimalNumber = match[3];

  // Entity references, see
  // https://spec.commonmark.org/0.30/#entity-references.
  if (entity != null) {
    return htmlEntitiesMap[text] ?? text;
  }

  // Decimal numeric character references, see
  // https://spec.commonmark.org/0.30/#decimal-numeric-character-references.
  else if (decimalNumber != null) {
    final decimalValue = int.parse(decimalNumber);
    int hexValue;
    if (decimalValue < 1114112 && decimalValue > 1) {
      hexValue = int.parse(decimalValue.toRadixString(16), radix: 16);
    } else {
      hexValue = 0xFFFd;
    }

    return String.fromCharCode(hexValue);
  }

  // Hexadecimal numeric character references, see
  // https://spec.commonmark.org/0.30/#hexadecimal-numeric-character-references.
  else if (hexadecimalNumber != null) {
    var hexValue = int.parse(hexadecimalNumber, radix: 16);
    if (hexValue > 0x10ffff || hexValue == 0) {
      hexValue = 0xFFFd;
    }
    return String.fromCharCode(hexValue);
  }

  return text;
}

extension MatchExtensions on Match {
  /// Returns the whole match String
  String get match => this[0]!;
}

/// Escapes the ASCII punctuation characters after backslash(`\`).
String escapePunctuation(String input) {
  final buffer = StringBuffer();

  for (var i = 0; i < input.length; i++) {
    if (input.codeUnitAt(i) == $backslash) {
      final next = i + 1 < input.length ? input[i + 1] : null;
      if (next != null && asciiPunctuationCharacters.contains(next)) {
        i++;
      }
    }
    buffer.write(input[i]);
  }

  return buffer.toString();
}