A "Game of Sorts"

main.dart

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
        backgroundColor: Colors.white,
        colorScheme: ColorScheme.light(),
      ),
      home: GameHome(),
    );
  }
}

class GameHome extends StatefulWidget {
  GameHome({Key key}) : super(key: key);
  @override
  _GameHomeState createState() => _GameHomeState();
}

class _GameHomeState extends State<GameHome> {
  int size = 4;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Game of Sorts"),),
      body: Row(
        children: <Widget>[
          Text("Choose board size:"),
          DropdownButton(items: [3, 4, 5].map((n) =>
              DropdownMenuItem(child: Text(n.toString() + "X" + n.toString()),
                value: n,)).toList(),
            onChanged: (v) {
              setState(() {
                size = v;
              });
            },
            value: size,
          ),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        child: IconButton(icon: Icon(Icons.play_arrow)),
        onPressed: () {
          Navigator.push(context, MaterialPageRoute(
              builder: (context) => GamePage(size),
          ));
        },
      ),
    );
  }

}

class GamePage extends StatefulWidget {
  GamePage(int this.size, {Key key}) : super(key: key);
  int size;
  @override
  _GamePageState createState() => _GamePageState(size, size);
}

class _GamePageState extends State<GamePage> {
  _GamePageState(this.rows, this.columns)
      : board = _initialBoard(rows, columns) {
    _shuffle();
  }
  final int rows;
  final int columns;
  final List<int> board;
  int moves = 0;

  static List<int> _initialBoard(int rows, int columns) {
    List<int> board = List<int>();
    for (int i = 1; i < rows * columns; i++) {
      board.add(i);
    }
    board.add(0);
    return board;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Sort of Fun...")),
      body: Center(child: _buildGame()),
      floatingActionButton: FloatingActionButton(
        child: IconButton(icon: Icon(Icons.shuffle)),
        onPressed: () {
          setState(() {
            _shuffle();
          });
        },
      ),
    );
  }

  void _shuffle() {
    Random rand = Random.secure();
    for (int i = 0; i < rows * rows * columns * columns * 4; i++) {
      _trySwap(rand.nextInt(rows * columns));
    }
    moves = 0;
  }

  Widget _buildGame() {
    return Column(
      children: <Widget>[
        Text(
          "Moves: " + moves.toString(),
          style: TextStyle(fontSize: 20),
        ),
        GridView.count(
          shrinkWrap: true,
          crossAxisCount: columns,
          padding: EdgeInsets.all(10),
          children: List<Widget>.generate(
            rows * columns,
            (n) => _buildCell(n),
          ),
        ),
      ],
    );
  }

  Widget _buildCell(int n) {
    int v = board.elementAt(n);
    if (v > 0) {
      return Container(
        padding: EdgeInsets.all(5),
        child: RaisedButton(
          child: Text(
            v.toString(),
            style: TextStyle(fontSize: 20),
          ),
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(20)),
          color: (v == n+1) ? Colors.blue : Colors.grey,
          onPressed: () {
            this.setState(() {
              _trySwap(n);
            });
          },
        ),
      );
    } else {
      return Container();
    }
  }

  void _trySwap(int n) {
    int column = n % columns;
    if (column > 0) {
      _swapZero(n, n - 1);
    }
    if (column < columns - 1) {
      _swapZero(n, n + 1);
    }
    _swapZero(n, n - columns);
    _swapZero(n, n + columns);
  }

  void _swapZero(int src, int dest) {
    if (dest < 0 || dest >= rows * columns) {
      return;
    }
    if (board[dest] == 0) {
      board[dest] = board[src];
      board[src] = 0;
      moves++;
    }
  }
}