import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:url_launcher/url_launcher.dart';

import '../../app/theme.dart';

/// Shows a bundled Markdown document (privacy policy, terms). Supports the
/// small subset those files use: #/## headings, "- " bullets, paragraphs,
/// **bold** and email addresses (tappable).
class DocumentScreen extends StatelessWidget {
  const DocumentScreen({super.key, required this.title, required this.asset});

  final String title;
  final String asset;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(title)),
      body: FutureBuilder<String>(
        future: rootBundle.loadString(asset),
        builder: (context, snap) {
          if (!snap.hasData) return const Center(child: CircularProgressIndicator());
          return SelectionArea(
            child: ListView(
              padding: const EdgeInsets.fromLTRB(20, 4, 20, 40),
              children: _render(context, snap.data!),
            ),
          );
        },
      ),
    );
  }

  List<Widget> _render(BuildContext context, String md) {
    final text = Theme.of(context).textTheme;
    final body = text.bodyLarge?.copyWith(color: NkColors.mutedOnPhoto, height: 1.55);
    final out = <Widget>[];
    for (final block in md.split(RegExp(r'\n\s*\n'))) {
      final lines = block.trim().split('\n');
      if (lines.first.isEmpty) continue;
      if (lines.first.startsWith('# ')) {
        continue; // the app bar already shows the title
      } else if (lines.first.startsWith('## ')) {
        out.add(Padding(
          padding: const EdgeInsets.only(top: 18, bottom: 6),
          child: Text(lines.first.substring(3), style: text.titleLarge),
        ));
      } else if (lines.every((l) => l.startsWith('- '))) {
        for (final l in lines) {
          out.add(Padding(
            padding: const EdgeInsets.only(bottom: 6),
            child: Row(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Text('•  ', style: body?.copyWith(color: NkColors.sun)),
                Expanded(child: Text.rich(_inline(l.substring(2), body), style: body)),
              ],
            ),
          ));
        }
        out.add(const SizedBox(height: 6));
      } else {
        out.add(Padding(
          padding: const EdgeInsets.only(bottom: 12),
          child: Text.rich(_inline(lines.join('\n'), body), style: body),
        ));
      }
    }
    return out;
  }

  /// **bold** and tappable email addresses.
  static TextSpan _inline(String s, TextStyle? base) {
    final spans = <InlineSpan>[];
    final pattern = RegExp(r'\*\*(.+?)\*\*|([\w.+-]+@[\w-]+(?:\.[\w-]+)+)');
    var last = 0;
    for (final m in pattern.allMatches(s)) {
      if (m.start > last) spans.add(TextSpan(text: s.substring(last, m.start)));
      if (m.group(1) != null) {
        spans.add(TextSpan(
          text: m.group(1),
          style: const TextStyle(fontWeight: FontWeight.w700, color: NkColors.cream),
        ));
      } else {
        final email = m.group(2)!;
        spans.add(TextSpan(
          text: email,
          style: const TextStyle(color: NkColors.sun),
          recognizer: TapGestureRecognizer()..onTap = () => launchUrl(Uri(scheme: 'mailto', path: email)),
        ));
      }
      last = m.end;
    }
    if (last < s.length) spans.add(TextSpan(text: s.substring(last)));
    return TextSpan(children: spans, style: base);
  }
}