Title case

strtotitle.php

<?php

function strtotitle(string $str): string {
    $title = mb_convert_case($str, MB_CASE_TITLE);
    
    // Edge cases
    return preg_replace_callback_array([
        "/('[a-z])/" => fn ($m) => strtoupper($m[1]),
        "/(\s(?:D(o|a)s?)\s)/" => fn ($m) => strtolower($m[1]),
    ], $title);
}


// TESTS
$tests = [
    ["Carlo D'ippoliti",    "Carlo D'Ippoliti"],
    ["Kerényi ádám",        "Kerényi Ádám"],
    ["Matteo Dell'aqcua",   "Matteo Dell'Aqcua"],
    ["john o'grady-smith",  "John O'Grady-Smith"],
    ["JOHN O'GRADY-SMITH2", "John O'Grady-Smith2"],
    ["john o'grady-smith5", "John O'Grady-Smith5"],
    ["joão da silva",       "João da Silva"],
    ["maria das dores",     "Maria das Dores"],
];

foreach ($tests as [$test, $expected]) {
    $actual = strtotitle($test);
    assert($actual === $expected, "Failed `{$test}` got `{$actual}` expecting `{$expected}`");
}