<?php
define('MINEGRID_WIDTH',  6);
define('MINEGRID_HEIGHT', 4);

define('MINESWEEPER_NOT_EXPLORED', -1);
define('MINESWEEPER_MINE',         -2);
define('MINESWEEPER_FLAGGED',      -3);
define('MINESWEEPER_FLAGGED_MINE', -4);
define('ACTIVATED_MINE',           -5);

function check_field($field) {
    if ($field === MINESWEEPER_MINE || $field === MINESWEEPER_FLAGGED_MINE) {
        return true;
    }
    else {
        return false;
    }
}

function explore_field($field) {
    if (!isset($_SESSION['minesweeper'][$field])
     || !in_array($_SESSION['minesweeper'][$field],
                  array(MINESWEEPER_NOT_EXPLORED, MINESWEEPER_FLAGGED))) {
        return;
    }

    $mines = 0;

    // Make reference to that long name
    $fields  = &$_SESSION['minesweeper'];

    // @ operator helps avoiding isset()... (it removes E_NOTICEs)

    // left side options
    if ($field % MINEGRID_WIDTH !== 1) {
        $mines += check_field(@$fields[$field - MINEGRID_WIDTH - 1]);
        $mines += check_field(@$fields[$field - 1]);
        $mines += check_field(@$fields[$field + MINEGRID_WIDTH - 1]);
    }

    // bottom and top
    $mines += check_field(@$fields[$field - MINEGRID_WIDTH]);
    $mines += check_field(@$fields[$field + MINEGRID_WIDTH]);

    // right side options
    if ($field % MINEGRID_WIDTH !== 0) {
        $mines += check_field(@$fields[$field - MINEGRID_WIDTH + 1]);
        $mines += check_field(@$fields[$field + 1]);
        $mines += check_field(@$fields[$field + MINEGRID_WIDTH + 1]);
    }

    $fields[$field] = $mines;

    if ($mines === 0) {
        if ($field % MINEGRID_WIDTH !== 1) {
            explore_field($field - MINEGRID_WIDTH - 1);
            explore_field($field - 1);
            explore_field($field + MINEGRID_WIDTH - 1);
        }

        explore_field($field - MINEGRID_WIDTH);
        explore_field($field + MINEGRID_WIDTH);

        if ($field % MINEGRID_WIDTH !== 0) {
            explore_field($field - MINEGRID_WIDTH + 1);
            explore_field($field + 1);
            explore_field($field + MINEGRID_WIDTH + 1);
        }
    }
}

session_start(); // will start session storage

if (!isset($_SESSION['minesweeper'])) {
    // Fill grid with not explored tiles
    $_SESSION['minesweeper'] = array_fill(1,
                                         MINEGRID_WIDTH * MINEGRID_HEIGHT,
                                         MINESWEEPER_NOT_EXPLORED);

    // Generate random number of mines between 0.1 and 0.2
    $number_of_mines = (int) mt_rand(0.1 * MINEGRID_WIDTH * MINEGRID_HEIGHT,
                                     0.2 * MINEGRID_WIDTH * MINEGRID_HEIGHT);

    // generate mines randomly
    $random_keys = array_rand($_SESSION['minesweeper'], $number_of_mines);

    foreach ($random_keys as $key) {
        $_SESSION['minesweeper'][$key] = MINESWEEPER_MINE;
    }

    // to make calculations shorter use SESSION variable to store the result
    $_SESSION['numberofmines'] = $number_of_mines;
}

if (isset($_GET['explore'])) {
    if(isset($_SESSION['minesweeper'][$_GET['explore']])) {
        switch ($_SESSION['minesweeper'][$_GET['explore']]) {
            case MINESWEEPER_NOT_EXPLORED:
                explore_field($_GET['explore']);
                break;
            case MINESWEEPER_MINE:
                $lost = 1;
                $_SESSION['minesweeper'][$_GET['explore']] = ACTIVATED_MINE;
                break;
            default:
                // The tile was discovered already. Ignore it.
                break;
        }
    }
    else {
        die('Tile doesn\'t exist.');
    }
}
elseif (isset($_GET['flag'])) {
    if(isset($_SESSION['minesweeper'][$_GET['flag']])) {
        $tile = &$_SESSION['minesweeper'][$_GET['flag']];
        switch ($tile) {
            case MINESWEEPER_NOT_EXPLORED:
                $tile = MINESWEEPER_FLAGGED;
                break;
            case MINESWEEPER_MINE:
                $tile = MINESWEEPER_FLAGGED_MINE;
                break;
            case MINESWEEPER_FLAGGED:
                $tile = MINESWEEPER_NOT_EXPLORED;
                break;
            case MINESWEEPER_FLAGGED_MINE:
                $tile = MINESWEEPER_MINE;
                break;
            default:
                // This tile shouldn't be flagged. Ignore it.
                break;
        }
    }
    else {
        die('Tile doesn\'t exist.');
    }
}

// Check if the player won...
if (!in_array(MINESWEEPER_NOT_EXPLORED, $_SESSION['minesweeper'])
 && !in_array(MINESWEEPER_FLAGGED,      $_SESSION['minesweeper'])) {
    $won = true;
}
?>
<!DOCTYPE html>
<title>Minesweeper</title>
<style>
table {
    border-collapse: collapse;
}

td, a {
    text-align:      center;
    width:           1em;
    height:          1em;
}

a {
    display:         block;
    color:           black;
    text-decoration: none;
    font-size:       2em;
}
</style>
<script>
function flag(number, e) {
    if (e.which === 2 || e.which === 3) {
        location = '?flag=' + number;
        return false;
    }
}
</script>
<?php
    echo "<p>This field contains $_SESSION[numberofmines] mines.";
?>
<table border="1">
<?php
// array_shift() affects array, so we need a copy
$mine_copy = $_SESSION['minesweeper'];

for ($x = 1; $x <= MINEGRID_HEIGHT; $x++) {
    echo '<tr>';
    for ($y = 1; $y <= MINEGRID_WIDTH; $y++) {
        echo '<td>';

        $number = array_shift($mine_copy);
        switch ($number) {
            case MINESWEEPER_FLAGGED:
            case MINESWEEPER_FLAGGED_MINE:
                if (!empty($lost) || !empty($won)) {
                    if ($number === MINESWEEPER_FLAGGED_MINE) {
                        echo '<a>*</a>';
                    }
                    else {
                        echo '<a>.</a>';
                    }
                }
                else {
                    echo '<a href=# onmousedown="return flag(',
                         ($x - 1) * MINEGRID_WIDTH + $y,
                         ',event)" oncontextmenu="return false">?</a>';
                }
                break;
            case ACTIVATED_MINE:
                echo '<a>:(</a>';
                break;
            case MINESWEEPER_MINE:
            case MINESWEEPER_NOT_EXPLORED:
                // oncontextmenu causes the menu to disappear in
                // Firefox, IE and Chrome

                // In case of Opera, modifying location causes menu
                // to not appear.

                if (!empty($lost)) {
                    if ($number === MINESWEEPER_MINE) {
                        echo '<a>*</a>';
                    }
                    else {
                        echo '<a>.</a>';
                    }
                }
                elseif (!empty($won)) {
                    echo '<a>*</a>';
                }
                else {
                    echo '<a href="?explore=',
                         ($x - 1) * MINEGRID_WIDTH + $y,
                         '" onmousedown="return flag(',
                         ($x - 1) * MINEGRID_WIDTH + $y,
                         ',event)" oncontextmenu="return false">.</a>';
                }
                break;
            case 0:
                echo '<a></a>';
                break;
            default:
                echo '<a>', $number, '</a>';
                break;
        }
    }
}
?>
</table>
<?php
if (!empty($lost)) {
    unset($_SESSION['minesweeper']);
    echo '<p>You lost :(. <a href="?">Reboot?</a>';
}
elseif (!empty($won)) {
    unset($_SESSION['minesweeper']);
    echo '<p>Congratulations. You won :).';
}