PHP Chess

<?php
$isValidChessBoard = true;
if (!isset($_GET['board'])) {
    $isValidChessBoard = false;
}
$boardRows = [];
if ($isValidChessBoard) {
    $boardRows = explode('/', $_GET['board']);
    if (count($boardRows) != 8) {
        $isValidChessBoard = false;
    }
}

$pieces = array('Bishop' => 0, 'Horseman' => 0, 'King' => 0, 'Pawn' => 0, 'Queen' => 0, 'Rook' => 0);
$board = [];
if ($isValidChessBoard) {
    foreach ($boardRows as $row) {
        $cells = explode('-', $row);
        if (count($cells) != 8) {
            $isValidChessBoard = false;
            break;
        }

        $board[] = $cells;
        foreach ($cells as $cell) {
            switch ($cell) {
                case 'B':
                    $pieces['Bishop'] += 1;
                    break;
                case 'H':
                    $pieces['Horseman'] += 1;
                    break;
                case 'K':
                    $pieces['King'] += 1;
                    break;
                case 'P':
                    $pieces['Pawn'] += 1;
                    break;
                case 'Q':
                    $pieces['Queen'] += 1;
                    break;
                case 'R':
                    $pieces['Rook'] += 1;
                    break;
                case ' ':
                    break;
                default:
                    $isValidChessBoard = false;
                    break;
            }
        }
    }
}

if (!$isValidChessBoard) {
    die('<h1>Invalid chess board</h1>');
}

echo '<table>';
foreach ($board as $tableRow) {
    $textRow = '<tr>';
    foreach ($tableRow as $tableCol) {
        $textRow .= "<td>{$tableCol}</td>";
    }
    echo $textRow . '</tr>';
}
echo '</table>';

foreach ($pieces as $key => &$value) {
    if ($value === 0) {
        unset($pieces[$key]);
    }
}

echo json_encode($pieces);