Add some colour

[JCKodel]

Since this parser doesn't render HTML, I made this custom syntax for colours:

#f00[This is red] renders Text("This is red", style: TextStyle(color: 0xffff0000)
#ff0000[This is red] renders Text("This is red", style: TextStyle(color: 0xffff0000)
#7fff0000[This is red] renders Text("This is red", style: TextStyle(color: 0x7fff0000)

It accepts 3 (RGB), 6 (RRGGBB) or 8 (AARRGGBB) hex codes.

class _ColorSyntax extends MdInlineSyntax {
  _ColorSyntax()
      : super(
          RegExp(r"#([0-9A-Fa-f]{3}|[0-9A-Fa-f]{6}|[0-9A-Fa-f]{8})\[([^\]]*)\]"),
        );

  @override
  MdInlineObject? parse(MdInlineParser parser, Match match) {
    final color = match.group(1)!;
    final text = match.group(2)!;

    final markers = [
      parser.consume(),
      ...parser.consumeBy(color.length),
      parser.consume(),
    ];

    final content = parser.consumeBy(text.length);

    markers.add(parser.consume());

    final children = content.map((e) => MdText.fromSpan(e)).toList();

    return MdInlineElement(
      "color",
      attributes: {"color": color},
      markers: markers,
      children: children,
      start: markers.first.start,
      end: children.last.end,
    );
  }
}

class _ColorBuilder extends MarkdownElementBuilder {
  _ColorBuilder();

  @override
  bool isBlock(element) => false;

  @override
  List<String> matchTypes = <String>["color"];

  @override
  TextStyle? buildTextStyle(MarkdownElement element, TextStyle defaultStyle) {
    final currentStyle = textStyle ?? textStyleMap?[element.type];
    final colorAttr = element.attributes["color"]!;

    final color = switch (colorAttr.length) {
      3 => _parseColor3(colorAttr),
      6 => _parseColor6(colorAttr),
      8 => _parseColor8(colorAttr),
      _ => throw FormatException("Unrecognized color pattern '${colorAttr}'"),
    };

    return defaultStyle
        .merge(parentStyle)
        .merge(currentStyle)
        .merge(TextStyle(color: color));
  }

  @override
  TextSpan buildText(
    String text,
    MarkdownTreeElement parent,
  ) =>
      TextSpan(
        text: text,
        style: parent.style,
        mouseCursor: renderer.mouseCursor,
      );

  Color _parseColor3(String color) {
    final r = color[0] + color[0];
    final g = color[1] + color[1];
    final b = color[2] + color[2];

    return Color(int.parse("ff$r$g$b", radix: 16));
  }

  Color _parseColor6(String color) {
    return Color(int.parse("ff${color}", radix: 16));
  }

  Color _parseColor8(String color) {
    return Color(int.parse(color, radix: 16));
  }
}

[chenzhiguang]

@JCKodel Thanks a lot! I will have a look at it later soon