<?php

function matrix($n)
{
    $result = [];

    for ($i = 0; $i < $n; $i++) {
        array_push($result, range(0, $n - 1));
    }

    $start_row = 0;
    $end_row = $n - 1;
    $start_column = 0;
    $end_column = $n - 1;

    $counter = 1;

    while ($start_row <= $end_row && $start_column <= $end_column) {
        for ($i = $start_column; $i <= $end_column; $i++) {
            $result[$start_row][$i] = $counter;
            $counter++;
        }
        $start_row++;

        for ($i = $start_row; $i <= $end_row; $i++) {
            $result[$i][$end_column] = $counter;
            $counter++;
        }
        $end_column--;

        for ($i = $end_column; $i >= $start_column; $i--) {
            $result[$end_row][$i] = $counter;
            $counter++;
        }
        $end_row--;

        for ($i = $end_row; $i >= $start_row; $i--) {
            $result[$i][$start_column] = $counter;
            $counter++;
        }
        $start_column++;
    }

    return $result;
}

// [[1,   2,  3, 4],
//  [12, 13, 14, 5],
//  [11, 16, 15, 6],
//  [10,  9,  8, 7]];

foreach (matrix(3) as $row) {
    echo join(', ', $row);
    echo "<br>";
}