import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:signature/signature.dart';

import '../../../../widget/info_dialog.dart';

/// Upper bound the server accepts for a signature image.
const int maxSignatureBytes = 256 * 1024;

/// Lets the guardian draw a signature. Resolves to the PNG (transparent
/// background, cropped to the strokes) or null when dismissed.
Future<Uint8List?> showSignatureSheet(
  BuildContext context, {
  required String signerHint,
}) => showModalBottomSheet<Uint8List>(
  context: context,
  isScrollControlled: true,
  enableDrag: false,
  showDragHandle: false,
  builder: (_) => _SignatureSheet(signerHint: signerHint),
);

class _SignatureSheet extends StatefulWidget {
  final String signerHint;

  const _SignatureSheet({required this.signerHint});

  @override
  State<_SignatureSheet> createState() => _SignatureSheetState();
}

class _SignatureSheetState extends State<_SignatureSheet> {
  // Paper-like pad in both themes: what is drawn is what gets exported.
  final SignatureController _controller = SignatureController(
    penStrokeWidth: 2.5,
    penColor: Colors.black,
    strokeCap: StrokeCap.round,
    strokeJoin: StrokeJoin.round,
  );

  @override
  void initState() {
    super.initState();
    _controller.addListener(_onChanged);
  }

  bool _isEmpty = true;

  // The controller notifies per drawn point; only the buttons depend on it.
  void _onChanged() {
    if (_controller.isEmpty == _isEmpty) return;
    setState(() => _isEmpty = _controller.isEmpty);
  }

  @override
  void dispose() {
    _controller.removeListener(_onChanged);
    _controller.dispose();
    super.dispose();
  }

  Future<void> _accept() async {
    var png = await _controller.toPngBytes();
    if (png != null && png.lengthInBytes > maxSignatureBytes) {
      png = await _controller.toPngBytes(width: 600);
    }
    if (!mounted) return;
    if (png == null || png.lengthInBytes > maxSignatureBytes) {
      InfoDialog.show(
        context,
        'Die Unterschrift konnte nicht übernommen werden. Bitte versuche es '
        'erneut.',
        title: 'Unterschrift',
      );
      return;
    }
    Navigator.pop(context, png);
  }

  @override
  Widget build(BuildContext context) => SafeArea(
    child: Padding(
      padding: const EdgeInsets.fromLTRB(16, 16, 16, 8),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: [
          Text('Unterschrift', style: Theme.of(context).textTheme.titleLarge),
          const SizedBox(height: 4),
          Text(widget.signerHint),
          const SizedBox(height: 12),
          ClipRRect(
            borderRadius: BorderRadius.circular(12),
            child: Signature(
              controller: _controller,
              height: 220,
              backgroundColor: Colors.white,
            ),
          ),
          const SizedBox(height: 8),
          Row(
            children: [
              TextButton.icon(
                onPressed: _isEmpty ? null : _controller.clear,
                icon: const Icon(Icons.undo),
                label: const Text('Löschen'),
              ),
              const Spacer(),
              TextButton(
                onPressed: () => Navigator.pop(context),
                child: const Text('Abbrechen'),
              ),
              const SizedBox(width: 8),
              FilledButton(
                onPressed: _isEmpty ? null : _accept,
                child: const Text('Übernehmen'),
              ),
            ],
          ),
        ],
      ),
    ),
  );
}