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}>[ ]?(.*)$');

/// 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}(`{3,}|~{3,})(.*)$');

/// 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('');