[Projeto] Solução para o desafio final

Essa foi a solução que consegui achar. Acho q ficou um pouco poluído, mas acredito que de pra entender.

class _TaskState extends State<Task> {
  int nivel = 0;
  int maestria = 0;
  double valor = 0;

  @override
  Widget build(BuildContext context) {
    return Padding(
        padding: const EdgeInsets.all(8.0),
        child: Stack(
          children: [
            Container(
                height: 140,
                decoration: BoxDecoration(
                  borderRadius: BorderRadius.circular(4),
                  color: (maestria == 0)
                      ? (Colors.blue)
                      : ((maestria == 1)
                          ? (Colors.green)
                          : (((maestria == 2)
                              ? (Colors.purple)
                              : ((maestria == 3)
                                  ? (Colors.amber)
                                  : ((maestria == 4)
                                      ? (Colors.red)
                                      : (Colors.red)))))),
                )
            ),
          .
          .
          .
                        SizedBox(
                          width: 52,
                          height: 52,
                          child: ElevatedButton(
                              onPressed: () {
                                setState(() {
                                  aumentoMaestria();
                                });
                              },
                              child: Column(
                                mainAxisAlignment:
                                    MainAxisAlignment.spaceEvenly,
                                crossAxisAlignment: CrossAxisAlignment.end,
                                children: const [
                                  Icon(Icons.arrow_drop_up),
                                  Text(
                                    'Up',
                                    style: TextStyle(
                                      fontSize: 12,
                               ),
                             ),
                           ],)
                          ),
                        )
                      ],)
                     ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  children: [
                    Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: SizedBox(
                          width: 200,
                          child: LinearProgressIndicator(
                              color: Colors.white,
                              value: (widget.dificuldade > 0)
                                  ? nivel / (widget.dificuldade * 10)
                                  : 1),
                        )),
                    Padding(
                      padding: const EdgeInsets.all(12.0),
                      child: Text(
                        'Nível: $nivel',
                        style:
                            const TextStyle(color: Colors.white, fontSize: 16),
                      ),
                    ),
                  ],
                )
              ],
            )
          ],
        ));
  }

  void aumentoMaestria() {
    nivel++;
    if (maestria > 4) {
      maestria -= 5;
    }
    return setState(() {
      if (nivel / (widget.dificuldade * 10) == 1) {
        maestria++;
        nivel = 0;
      }
    });
  }
}