PHP Markov Chain

<?php
$lf = str_replace('/', '-', (isset($_REQUEST['lx'])?$_REQUEST['lx']:'en-f')) . '.json';
$lex = json_decode(file_get_contents('./lexicons/' . $lf), true);
$q = isset($_REQUEST['q'])?$_REQUEST['q']:'';

function nextWord($w) {
    global $lex;
    if(array_key_exists($w, $lex)) {
        return $lex[$w][rand(0, count($lex[$w])-1)];
    } else return null;
}
function endsWith($haystack, $needle) {
    return $needle === "" || (($temp = strlen($haystack) - strlen($needle)) >= 0 && strpos($haystack, $needle, $temp) !== false);
}
function endsWithPunctuations($t) {
    $p = str_split('(),.?!');
    $r = false;
    foreach($p as $n) {
        if(endsWith($t, $n)) $r = true;
    }
    return $r;
}

if(strlen($q) < 1) {
    die;
}
$t = explode(' ', $q);
if(count($t) > 1) {
    $u = array_unique($t);
    foreach($u as $i => $c) {
        if(array_key_exists($c, $lex))
            $w = $lex[$c];
        else
            $w = [];
        for($n = 0; $n < count($t); $n++) {
            if($c == $t[$n] && !endsWithPunctuations($t[$n])) {
                array_push($w, $t[$n+1]);
            }
        }
        $lex[$c] = array_values(array_unique($w));
    }
    file_put_contents('./lexicons/' . $lf, strtolower(json_encode($lex)));
}
$s = $t[rand(0, count($t)-1)];
dbg('RndWrd: ' . $s);
if(array_key_exists($s, $lex)) {
    dbg('Constructing setnence');
    $r = $s;
    $words = 0;
    while(true) {
        $nw = nextWord($s);
        if($nw == null) break;
        dbg('NxtWrd: ' . $nw);
        $r .= ' ' . $nw;
        $s = $nw;
        if(endsWithPunctuations($nw, -1)) break;
        $words++;
        if($words > 50) break;
    }
    echo str_replace('  ', ' ', $r);
} else echo 'What?';
?>