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])*$');

/// 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(r'^([ ]{0,3})()([*+-])(([ \t])([ \t]*)(.*))?$');

/// 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(r'^([ ]{0,3})(\d{1,9})([\.)])(([ \t])([ \t]*)(.*))?$');

/// 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('');