super_tik_tac_toe/lib/main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Super Tic-Tac-Toe',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Local Tic Tac Toe'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  TTCState turn = TTCState.x;
  late TTCGame game;

  String get turnText => switch (turn) {
        TTCState.empty => "",
        TTCState.x => "X",
        TTCState.o => "O",
      };

  void onTurnEnd() {
    setState(() {
      turn = switch (turn) {
        TTCState.x => TTCState.o,
        TTCState.o => TTCState.x,
        _ => TTCState.x
      };
    });
  }

  @override
  void initState() {
    super.initState();
    game = TTCGame(
      turn: turn,
      onClick: onTurnEnd,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
      ),
      body: Padding(
          padding: const EdgeInsets.all(10),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              const Spacer(flex: 5),
              Center(
                  child: Text(
                "$turnText's turn",
                style:
                    const TextStyle(fontSize: 30, fontWeight: FontWeight.bold),
              )),
              const Spacer(flex: 1),
              TTCGame(
                turn: turn,
                onClick: onTurnEnd,
              ),
              const Spacer(flex: 5),
            ],
          )),
    );
  }
}

enum TTCState { empty, x, o }

/// Board of a single game of tic tac toe
class TTCGame extends StatefulWidget {
  const TTCGame({
    super.key,
    required this.turn,
    this.data,
    this.onClick,
  });

  final TTCState turn;
  final List<TTCState>? data;

  /// hook into acction of tapping on square
  final Function? onClick;

  @override
  State<StatefulWidget> createState() => _TTCGameState();
}

class _TTCGameState extends State<TTCGame> {
  late TTCState turn;
  late List<TTCState> data;

  void setCellState(int index) {
    switch (data[index]) {
      case TTCState.empty:
        setState(() {
          data[index] = turn;

          turn = switch (turn) {
            TTCState.x => TTCState.o,
            TTCState.o => TTCState.x,
            TTCState.empty => TTCState.empty,
          };
        });
        widget.onClick?.call();
        notifyWin();
        break;
      default:
        ScaffoldMessenger.of(context)
          ..clearSnackBars()
          ..showSnackBar(const SnackBar(
              content: Text("Invalid Choice: cell already has value")));
    }
  }

  Iterable<TTCState> getRow(int index) => data.getRange(index, index + 3);
  Iterable<TTCState> getCol(int index) => [
        data[index],
        data[index + 3],
        data[index + 3 * 2],
      ];
  Iterable<TTCState> getCross(int index) {
    if (index == 0) {
      return [data[0], data[4], data[8]];
    }
    return [data[3], data[4], data[6]];
  }

  TTCState _checkRow(Iterable<TTCState> row) => row.reduce((value, element) =>
      (element == TTCState.empty || value == TTCState.empty || element != value)
          ? TTCState.empty
          : value);

  TTCState _checkBoard(Iterable<TTCState> rowValues) =>
      rowValues.reduce((value, element) {
        if (value != TTCState.empty) {
          return value;
        }
        if (element != TTCState.empty) {
          return element;
        }

        return TTCState.empty;
      });

  TTCState _checkWin() {
    Iterable<TTCState> rows = Iterable.generate(3, (i) => _checkRow(getRow(i)));
    Iterable<TTCState> cols = Iterable.generate(3, (i) => _checkRow(getCol(i)));
    Iterable<TTCState> crosses =
        Iterable.generate(2, (i) => _checkRow(getCross(i)));

    return _checkBoard([...rows, ...cols, ...crosses]);
  }

  void notifyWin() {
    TTCState state = _checkWin();

    if (state != TTCState.empty) {
      ScaffoldMessenger.of(context)
        ..clearSnackBars()
        ..showSnackBar(
            SnackBar(content: Text("${state.name.toUpperCase()} wins")));
    }
  }

  Border _genCellBorder(
    int index, {
    BorderSide borderSide = const BorderSide(),
  }) {
    return Border(
      top: index < 3 ? BorderSide.none : borderSide,
      bottom: index > 5 ? BorderSide.none : borderSide,
      left: [0, 3, 6].contains(index) ? BorderSide.none : borderSide,
      right: [2, 5, 8].contains(index) ? BorderSide.none : borderSide,
    );
  }

  Widget _genCell(int index, TTCState state) => Container(
      decoration: BoxDecoration(border: _genCellBorder(index)),
      child: TTCCell(
        state: state,
        stateSetCallback: () {
          setCellState(index);
        },
      ));

  @override
  void initState() {
    super.initState();
    turn = widget.turn;
    data = widget.data ??
        <TTCState>[
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
          TTCState.empty,
        ];
  }

  @override
  Widget build(BuildContext context) {
    List<Widget> cells = [];
    for (final (index, state) in data.indexed) {
      cells.add(_genCell(index, state));
    }
    return GridView.count(
      crossAxisCount: 3,
      shrinkWrap: true,
      children: cells,
    );
  }
}

class TTCCell extends StatelessWidget {
  const TTCCell({
    super.key,
    required this.state,
    this.stateSetCallback,
    this.textStyle,
  });

  final TTCState state;
  final VoidCallback? stateSetCallback;
  final TextStyle? textStyle;

  String get text => switch (state) {
        TTCState.empty => "",
        TTCState.x => "X",
        TTCState.o => "O",
      };

  @override
  Widget build(BuildContext context) => InkWell(
      onTap: stateSetCallback,
      child: Center(
        child: Text(text, style: textStyle),
      ));
}