Consent rich text

consent_text.dart

import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:localization/localization.dart';

/*
 * I consent to the processing of personal data,
 * the use of <c>cookies</c>,
 * agree to the <t>terms and conditions</t>,
 * and acknowledge the <p>privacy policy</p>.
 */

/// {@template consent_text}
/// A text widget that displays a consent message with clickable links for
/// cookies, terms of service, and privacy policy.
/// {@endtemplate}
class ConsentText extends StatefulWidget {
  /// {@macro consent_text}
  const ConsentText({
    required this.onCookiesTap,
    required this.onTermsTap,
    required this.onPrivacyTap,
    this.textStyle,
    this.linkStyle,
    this.textAlign,
    this.maxLines,
    this.overflow,
    super.key,
  });

  /// Callback when the "cookies" link is tapped.
  final VoidCallback onCookiesTap;

  /// Callback when the "terms and conditions" link is tapped.
  final VoidCallback onTermsTap;

  /// Callback when the "privacy policy" link is tapped.
  final VoidCallback onPrivacyTap;

  /// The style to use for the main text.
  final TextStyle? textStyle;

  /// The style to use for the links.
  final TextStyle? linkStyle;

  /// How the text should be aligned horizontally.
  final TextAlign? textAlign;

  /// The maximum number of lines for the text to span, wrapping if necessary.
  final int? maxLines;

  /// How visual overflow should be handled.
  final TextOverflow? overflow;

  @override
  State<ConsentText> createState() => _ConsentTextState();
}

/// State for widget ConsentText.
class _ConsentTextState extends State<ConsentText> {
  static const String _cookiesTag = 'c';
  static const String _termsTag = 't';
  static const String _privacyTag = 'p';
  static final RegExp _tagRegExp = RegExp(r'<(c|t|p)>(.*?)</\1>', dotAll: true);

  late TapGestureRecognizer _cookiesRecognizer;
  late TapGestureRecognizer _termsRecognizer;
  late TapGestureRecognizer _privacyRecognizer;
  late SignUpLocalization _l10n;
  late ThemeData _theme;
  late List<InlineSpan> _spans;
  late TextStyle _textStyle;
  late String _semanticText;

  /// Gets the computed link style
  TextStyle get _linkStyle =>
      widget.linkStyle ?? _textStyle.copyWith(color: _theme.colorScheme.primary, decoration: TextDecoration.underline);

  // Cache for avoiding unnecessary rebuilds
  String? _cachedRawText;
  TextStyle? _cachedTextStyle;
  TextStyle? _cachedLinkStyle;

  @override
  void initState() {
    super.initState();
    _cookiesRecognizer = TapGestureRecognizer()..onTap = widget.onCookiesTap;
    _termsRecognizer = TapGestureRecognizer()..onTap = widget.onTermsTap;
    _privacyRecognizer = TapGestureRecognizer()..onTap = widget.onPrivacyTap;
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    _l10n = SignUpLocalization.of(context);
    _theme = Theme.of(context);
    _textStyle = widget.textStyle ?? DefaultTextStyle.of(context).style;

    // Only rebuild if dependencies actually changed
    if (_shouldRebuildSpans()) {
      _rebuildSpans();
    }
  }

  @override
  void didUpdateWidget(covariant ConsentText oldWidget) {
    super.didUpdateWidget(oldWidget);

    // Update recognizers only if callbacks changed
    if (oldWidget.onCookiesTap != widget.onCookiesTap) {
      _cookiesRecognizer.onTap = widget.onCookiesTap;
    }
    if (oldWidget.onTermsTap != widget.onTermsTap) {
      _termsRecognizer.onTap = widget.onTermsTap;
    }
    if (oldWidget.onPrivacyTap != widget.onPrivacyTap) {
      _privacyRecognizer.onTap = widget.onPrivacyTap;
    }

    // Update text style if changed
    if (oldWidget.textStyle != widget.textStyle) {
      _textStyle = widget.textStyle ?? DefaultTextStyle.of(context).style;
    }

    // Only rebuild if styles changed
    if (oldWidget.textStyle != widget.textStyle || oldWidget.linkStyle != widget.linkStyle) {
      _rebuildSpans();
    }
  }

  @override
  void dispose() {
    _cookiesRecognizer.dispose();
    _termsRecognizer.dispose();
    _privacyRecognizer.dispose();
    super.dispose();
  }

  /// Checks if spans need to be rebuilt based on cached values
  bool _shouldRebuildSpans() {
    final rawText = _l10n.consentFull;
    final linkStyle = _linkStyle;
    return _cachedRawText != rawText || _cachedTextStyle != _textStyle || _cachedLinkStyle != linkStyle;
  }

  // Parser for tags <c>...</c>, <t>...</t>, <p>...</p>
  static List<InlineSpan> _buildTaggedSpans(
    String input, {
    required TextStyle base,
    required TextStyle link,
    required Map<String, TapGestureRecognizer> recognizers,
  }) {
    final spans = <InlineSpan>[];
    var cursor = 0;

    for (final match in _tagRegExp.allMatches(input)) {
      // Add text before the tag
      if (match.start > cursor) spans.add(TextSpan(text: input.substring(cursor, match.start), style: base));

      final tag = match.group(1);
      final text = match.group(2);

      if (tag != null && text != null) {
        final recognizer = recognizers[tag];
        if (recognizer != null) {
          spans.add(
            TextSpan(
              text: text,
              style: link,
              recognizer: recognizer,
              mouseCursor: SystemMouseCursors.click,
              semanticsLabel: text,
            ),
          );
        } else {
          // Fallback if recognizer not found
          assert(false, 'ConsentText: Unknown tag "$tag" in consent text');
          spans.add(TextSpan(text: text, style: base));
        }
      }
      cursor = match.end;
    }

    // Add remaining text after the last tag
    if (cursor < input.length) spans.add(TextSpan(text: input.substring(cursor), style: base));

    return spans;
  }

  void _rebuildSpans() {
    final rawText = _l10n.consentFull;
    _semanticText = rawText.replaceAll(RegExp(r'</?[ctp]>'), '');

    final linkStyle = _linkStyle;

    try {
      _spans = _buildTaggedSpans(
        rawText,
        base: _textStyle,
        link: linkStyle,
        recognizers: <String, TapGestureRecognizer>{
          _cookiesTag: _cookiesRecognizer,
          _termsTag: _termsRecognizer,
          _privacyTag: _privacyRecognizer,
        },
      );

      // Update cache
      _cachedRawText = rawText;
      _cachedTextStyle = _textStyle;
      _cachedLinkStyle = linkStyle;
    } on Object catch (e) {
      assert(false, 'ConsentText: Error parsing tagged text: $e');
      // Fallback to plain text
      _spans = <InlineSpan>[TextSpan(text: _semanticText, style: _textStyle)];
    }
  }

  @override
  Widget build(BuildContext context) => Text.rich(
    TextSpan(children: _spans, style: _textStyle),
    textAlign: widget.textAlign,
    maxLines: widget.maxLines,
    overflow: widget.overflow ?? TextOverflow.clip,
    textWidthBasis: TextWidthBasis.parent,
    softWrap: true,
    semanticsLabel: _semanticText,
  );
}