lib/src/patterns.dart

// Copyright (c) 2022, 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.

/// The line contains only whitespace or is empty.
final emptyPattern = RegExp(r'^(?:[ \t]*)$');

/// A series of `=` or `-` (on the next line) define setext-style headers.
final setextPattern = RegExp(r'^[ ]{0,3}(=+|-+)\s*$');

/// Leading (and trailing) `#` define atx-style headers.
///
/// Starts with 1-6 unescaped `#` characters which must not be followed by a
/// non-space character. Line may end with any number of `#` characters,.
final headerPattern = RegExp(r'^ {0,3}(#{1,6})[ \x09\x0b\x0c](.*?)#*$');

/// The line starts with `>` with one optional space after.
final blockquotePattern = RegExp(r'^[ ]{0,3}>[ \t]?.*$');

/// A line indented four spaces. Used for code blocks and lists.
final indentPattern = RegExp(r'^(?:    | {0,3}\t)(.*)$');

/// Fenced code block.
final codeFencePattern = RegExp(
  r'^([ ]{0,3})(?:(?<backtick>`{3,})(?<backtickInfo>[^`]*)|(?<tilde>~{3,})(?<tildeInfo>.*))$',
);

/// Fenced blockquotes.
final blockquoteFencePattern = RegExp(r'^>{3}\s*$');

/// Three or more hyphens, asterisks or underscores by themselves. Note that
/// a line like `----` is valid as both HR and SETEXT. In case of a tie,
/// SETEXT should win.
final hrPattern = RegExp(r'^ {0,3}([-*_])[ \t]*\1[ \t]*\1(?:\1|[ \t])*$');

// why `{1}`?
const _checkbox = r'\[[ xX]{1}\]';

const _groupedWhitespaceAndEverything = r'([ \t])([ \t]*)(.*)';

const _oneToNineDigits = r'\d{1,9}';

const _zeroToFourWhitespace = r'[ \t]{0,4}';

const _zeroToThreeSpaces = '[ ]{0,3}';

/// A line starting with one of these markers: `-`, `*`, `+`.
///
/// May have up to three leading spaces before the marker and any number of
/// spaces or tabs after.
///
/// Contains a dummy group at `[2]`, so that the groups in [ulPattern] and
/// [olPattern] match up; in both, `[2]` is the length of the number that begins
/// the list marker.
final ulPattern = RegExp(''
    '^($_zeroToThreeSpaces)'
    // Empty group for group number alignment with [olPattern].
    '()'
    '([*+-])'
    '($_groupedWhitespaceAndEverything)?\$');

/// Similar to [ulPattern] but with a GitHub-style checkbox
/// (`'[ ]'|'[x]'|'[X]'`) following the number.
///
/// The checkbox will be grabbed by group `[5]` and [ulPattern]'s groups
/// `[4]`, `[5]`, and `[6]` are all shifted 2 places to be `[6]`, `[7]`, and
/// `[8]`.
final ulWithCheckBoxPattern = RegExp(''
    '^($_zeroToThreeSpaces)'
    // Empty group for group number alignment with [olWithCheckBoxPattern].
    '()'
    '([*+-])'
    '($_zeroToFourWhitespace)'
    '($_checkbox)'
    '($_groupedWhitespaceAndEverything)?\$');

/// Similar to [ulWithCheckBoxPattern] but the checkbox is optional.
// TODO(srawlins): This is temporary tech debt. I think we will collapse
// [ulPattern] and [ulWithCheckBoxPattern] into this one pattern.
final ulWithPossibleCheckboxPattern = RegExp(''
    '^($_zeroToThreeSpaces)'
    // Empty group for group number alignment with [olWithCheckBoxPattern].
    '()'
    '([*+-])'
    '(($_zeroToFourWhitespace)($_checkbox))?'
    // [7], [8], [9], and [10].
    '($_groupedWhitespaceAndEverything)?\$');

/// A line starting with a number like `123.`. May have up to three leading
/// spaces before the marker and any number of spaces or tabs after.
final olPattern = RegExp(''
    '^($_zeroToThreeSpaces)'
    '($_oneToNineDigits)'
    r'([\.)])'
    '($_groupedWhitespaceAndEverything)?\$');

/// Similar to [olPattern] but with a GitHub-style checkbox
/// (`'[ ]'|'[x]'|'[X]'`) following the number.
///
/// The checkbox will be grabbed by group `[5]` and [olPattern]'s groups
/// `[4]`, `[5]`, and `[6]` are all shifted 2 places to be `[6]`, `[7]`, and
/// `[8]`.
final olWithCheckBoxPattern = RegExp(''
    '^($_zeroToThreeSpaces)'
    '($_oneToNineDigits)'
    r'([\.)])'
    '($_zeroToFourWhitespace)'
    '($_checkbox)'
    '($_groupedWhitespaceAndEverything)?\$');

/// Similar to [olWithCheckBoxPattern] but the checkbox is optional.
// TODO(srawlins): This is temporary tech debt. I think we will collapse
// [olPattern] and [olWithCheckBoxPattern] into this one pattern.
final olWithPossibleCheckboxPattern = RegExp(''
    '^($_zeroToThreeSpaces)'
    '($_oneToNineDigits)'
    r'([\.)])'
    '(($_zeroToFourWhitespace)($_checkbox))?'
    // [7], [8], [9], and [10].
    '($_groupedWhitespaceAndEverything)?\$');

/// A line of hyphens separated by at least one pipe.
final tablePattern = RegExp(
    r'^[ ]{0,3}\|?([ \t]*:?\-+:?[ \t]*\|)+([ \t]|[ \t]*:?\-+:?[ \t]*)?$');

/// A pattern which should never be used. It just satisfies non-nullability of
/// pattern fields.
final dummyPattern = RegExp('');

/// A [String] pattern to match a named tag like `<table>` or `</table>`.
const namedTagDefinition =
    // Opening tag begins.
    '<'

    // Tag name.
    '[a-z][a-z0-9-]*'

    // Attribute begins, see
    // https://spec.commonmark.org/0.30/#attribute.
    r'(?:\s+'

    // Attribute name, see
    // https://spec.commonmark.org/0.30/#attribute-name.
    '[a-z_:][a-z0-9._:-]*'

    //
    '(?:'
    // Attribute value specification, see
    // https://spec.commonmark.org/0.30/#attribute-value-specification.
    r'\s*=\s*'

    // Attribute value, see
    // https://spec.commonmark.org/0.30/#unquoted-attribute-value.
    r'''(?:[^\s"'=<>`]+?|'[^']*?'|"[^"]*?")'''

    // Attribute ends.
    ')?)*'

    // Opening tag ends.
    r'\s*/?>'

    // Or
    '|'

    // Closing tag, see
    // https://spec.commonmark.org/0.30/#closing-tag.
    r'</[a-z][a-z0-9-]*\s*>';

/// A pattern to match the start of an HTML block.
///
/// The 7 conditions here correspond to the 7 start conditions in the Commonmark
/// specification one by one: https://spec.commonmark.org/0.30/#html-block.
final htmlBlockPattern = RegExp(
    '^ {0,3}(?:'
    '<(?<condition_1>pre|script|style|textarea)'
    r'(?:\s|>|$)'
    '|'
    '(?<condition_2><!--)'
    '|'
    r'(?<condition_3><\?)'
    '|'
    '(?<condition_4><![a-z])'
    '|'
    r'(?<condition_5><!\[CDATA\[)'
    '|'
    '</?(?<condition_6>address|article|aside|base|basefont|blockquote|body|'
    'caption|center|col|colgroup|dd|details|dialog|dir|DIV|dl|dt|fieldset|'
    'figcaption|figure|footer|form|frame|frameset|h1|h2|h3|h4|h5|h6|head|'
    'header|hr|html|iframe|legend|li|link|main|menu|menuitem|nav|noframes|ol|'
    'optgroup|option|p|param|section|source|summary|table|tbody|td|tfoot|th|'
    'thead|title|tr|track|ul)'
    r'(?:\s|>|/>|$)'
    '|'

    // Here we are more restrictive than the Commonmark definition (Rule #7).
    // Otherwise some raw HTML test cases will fail, for example:
    // https://spec.commonmark.org/0.30/#example-618.
    // Because if a line is treated as an HTML block, it will output as Text node
    // directly, the RawHtmlSyntax does not have a chance to validate if this
    // HTML tag is legal or not.
    '(?<condition_7>(?:$namedTagDefinition)\\s*\$))',
    caseSensitive: false);

/// ASCII punctuation characters.
// See https://spec.commonmark.org/0.30/#unicode-whitespace-character.
const asciiPunctuationCharacters = r'''!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~''';

/// ASCII punctuation characters with some characters escaped, in order to be
// used in the RegExp character set.
const asciiPunctuationEscaped = r'''!"#$%&'()*+,\-./:;<=>?@\[\\\]^_`{|}~''';

/// A pattern to match HTML entity references and numeric character references.
// https://spec.commonmark.org/0.30/#entity-and-numeric-character-references
final htmlCharactersPattern = RegExp(
  '&(?:([a-z0-9]+)|#([0-9]{1,7})|#x([a-f0-9]{1,6}));',
  caseSensitive: false,
);