import 'dart:async';
import 'dart:math';

import 'package:flutter/material.dart';

/// Simple binary rain animation with a label for the update check splash.
class UpdateCheckingScreen extends StatefulWidget {
  const UpdateCheckingScreen({super.key});

  @override
  State<UpdateCheckingScreen> createState() => _UpdateCheckingScreenState();
}

class _UpdateCheckingScreenState extends State<UpdateCheckingScreen> {
  static const int cols = 20;
  final List<_Drop> _drops = [];
  Timer? _timer;
  final Random _rng = Random();

  @override
  void initState() {
    super.initState();
    _timer = Timer.periodic(const Duration(milliseconds: 50), (_) {
      _tick();
    });
  }

  void _tick() {
    setState(() {
      if (_rng.nextDouble() < 0.3 || _drops.isEmpty) {
        _drops.add(
          _Drop(
            col: _rng.nextInt(cols),
            y: 0.0,
            speed: _rng.nextDouble() * 4 + 2,
          ),
        );
      }
      _drops.removeWhere((d) => d.y > MediaQuery.of(context).size.height);
      for (final d in _drops) {
        d.y += d.speed;
      }
    });
  }

  @override
  void dispose() {
    _timer?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final cs = Theme.of(context).colorScheme;
    return Scaffold(
      backgroundColor: cs.surface,
      body: SafeArea(
        child: Column(
          children: [
            const SizedBox(height: 40),
            Hero(
              tag: 'tasq-logo',
              child: Image.asset('assets/tasq_ico.png', height: 80, width: 80),
            ),
            const SizedBox(height: 24),
            Expanded(
              child: CustomPaint(
                size: Size.infinite,
                painter: _BinaryRainPainter(_drops, cols, cs.primary),
              ),
            ),
            const SizedBox(height: 24),
            Text(
              'Checking for updates...',
              style: Theme.of(context).textTheme.titleMedium?.copyWith(
                color: cs.onSurface.withAlpha((0.75 * 255).round()),
              ),
            ),
            const SizedBox(height: 40),
          ],
        ),
      ),
    );
  }
}

class _Drop {
  int col;
  double y;
  double speed;
  _Drop({required this.col, required this.y, required this.speed});
}

class _BinaryRainPainter extends CustomPainter {
  static const double fontSize = 16;
  final List<_Drop> drops;
  final int cols;
  final Color textColor;

  _BinaryRainPainter(this.drops, this.cols, this.textColor);

  @override
  void paint(Canvas canvas, Size size) {
    // paint variable not needed when drawing text
    final textStyle = TextStyle(
      color: textColor,
      fontSize: fontSize,
      fontFeatures: const [FontFeature.tabularFigures()],
    );
    final cellW = size.width / cols;

    for (final d in drops) {
      final text = (Random().nextBool() ? '1' : '0');
      final tp = TextPainter(
        text: TextSpan(text: text, style: textStyle),
        textAlign: TextAlign.center,
        textDirection: TextDirection.ltr,
      )..layout();
      final x = d.col * cellW + (cellW - tp.width) / 2;
      final y = d.y;
      tp.paint(canvas, Offset(x, y));
    }
  }

  @override
  bool shouldRepaint(covariant _BinaryRainPainter old) => true;
}