import 'dart:async';

import 'package:flutter/material.dart';

const colors = [Colors.red, Colors.blue, Colors.yellow],
    a = LinearGradient(colors: colors, transform: GradientRotation(1.57)),
    b = LinearGradient(colors: colors, transform: GradientRotation(2.36)),
    t = 0.0,
    kTickSec = 5;

/// The `lerp` gradient should be more-or-less identical to `a` when
/// `t == 0.0`; look like `b` when `t == 1.0`; and should at least have
/// the GradientTransform of either when `t` is any other value, such as
/// for TileMode:
///     transform: t < 0.5 ? a.transform : b.transform
final lerp = LinearGradient.lerp(a, b, t)!;

void main() => runApp(const MyApp());

class MyApp extends StatefulWidget {
  const MyApp({super.key});
  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  var index = 0;
  late Timer timer;

  void incrementGradient() =>
      mounted ? setState(() => index = (index == 2) ? 0 : index + 1) : null;

  @override
  void initState() {
    super.initState();
    timer = Timer.periodic(
        const Duration(seconds: kTickSec), (timer) => incrementGradient());
  }

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

  Gradient get gradient => switch (index) { 0 => a, 1 => b, _ => lerp };

  @override
  Widget build(BuildContext context) {
    final gradient = this.gradient;
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: DecoratedBox(
            decoration: BoxDecoration(gradient: gradient),
            child: Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                children: [
                  Center(
                      child: Text(
                          '$index\n${switch (index) {
                            0 => 'LinearGradient a',
                            1 => 'LinearGradient b',
                            _ =>
                              'LinearGradient.lerp(a, b, ${t.toStringAsFixed(1)})'
                          }}',
                          style: const TextStyle(fontSize: 40),
                          textAlign: TextAlign.center)),
                  Padding(
                      padding: const EdgeInsets.symmetric(horizontal: 25),
                      child: Center(
                          child: Text(
                        '$gradient',
                        style: const TextStyle(fontSize: 20),
                      ))),
                  Center(
                      child: Text(
                    '${gradient.transform}',
                    style: const TextStyle(fontSize: 26),
                  )),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }
}