(() => {
    "use strict";

    const game = () => {
        let done;
        const solutions = [
            [ 0, 1, 2 ], [ 0, 3, 6 ], [ 0, 4, 8 ],
            [ 1, 4, 7 ], [ 2, 4, 6 ], [ 2, 5, 8 ],
            [ 3, 4, 5 ], [ 6, 7, 8 ]
        ];

        const check = abc => abc.filter(e => board[e] !== ' '
                                          && board[e] === board[abc[0]])
                                .length === 3;

        const win = (...args) => {
            done = args;
        };

        const board = new Proxy([...'         '], {
            set: (t, k, v) => {
                if (t[k] === ' ') {
                    t[k] = v;
                } else {
                    return false;
                }

                const correct = solutions.filter(e => e.includes(+k) && check(e));

                if (correct.length > 0) win(k, v, correct);

                return true;
            },
            get: (t, k) => { return t[k]; },
        });

        const render = message => {
            const b = board;

            return `
                ${ message }

                    0: ${ b[0] } | 1: ${ b[1] } | 2: ${ b[2] }
                    3: ${ b[3] } | 4: ${ b[4] } | 5: ${ b[5] }
                    6: ${ b[6] } | 7: ${ b[7] } | 8: ${ b[8] }`;
        };

        const play = (() => {
            let turn = 0;

            return () => {
                if(done) {
                    const [k, v, correct] = done;
                    if(confirm(render(`${ v } won! play again?`))) {
                        game();
                    }
                    return false;
                }

                if(turn > 8) {
                    if(confirm(render(`Game over, play again?`))) {
                        game();
                    }
                    return false;
                }

                const value = ['X', 'O'][turn++ % 2];

                const index = prompt(render(`Player ${ value }, choose a space:`));

                if(index === null) {
                    if(confirm(render(`${ value } forfeit the game, play again?`))) {
                        game();
                    }
                    return false;
                }

                if(!(index in board)) {
                    if(confirm(render(`${ index } is an invalid index, try again?`))) {
                        play(--turn);
                    }
                    return false;
                }

                try {
                    board[+index] = value;
                    play();
                } catch(e) {
                    if(confirm(render(`${ index } is occupied, choose again?`))) {
                        play(--turn);
                    }
                }
            };
        })();

        return play();
    };

    game();
})();