<?php

$strs = ['c0', 'c0-3', 'c0+3', 'c0 & 9', 'c0001, 2, 03', 'c01-03', 'c1.0 - 2.0', 'chapter 2A Hello', 'chapter 2AHello', 'chapter 10.4c', 'chapter 2B', 'episode 23.000 & 00024', 'episode 23 & 24', 'e23 & 24', 'text c25.6 text', '001 & 2 & 5 & 8-20 & 100 text chapter 25.6 text 98', 'hello 23 & 24', 'ep 1 - 2', 'chapter 1 - chapter 2', 'text chapter 25.6 text', 'text chapters 23, 24, 25 text','text chapter 23, 25 text', 'text chapter 23 & 24 & 25 text','text c25.5-30 text', 'text c99-c102 text', 'text chapter 1 - 3 text', '33 text chapter 1, 2 text 3','text chapters 23, 24, 25, 29, 31, 32 text', 'c19 & c20', 'chapter 25.6 & chapter 29', 'chapter 25+c26', 'chapter 25 + 26 + 27'];
$terms = ['episode', 'chapter', 'ch', 'ep', 'c', 'e', ''];

usort($terms, function($a, $b) {
    return strlen($b) - strlen($a);
});
 
$chapter_main_rx = "\b(?|" . implode("|", array_map(function ($term) {
	return strlen($term) > 0 ? "(" . substr($term, 0, 1) . ")(" . substr($term, 1) . "s?)": "()()" ;},
  $terms)) . ")\s*";
$chapter_aux_rx = "\b(?:" . implode("|", array_map(function ($term) {
	return strlen($term) > 0 ? substr($term, 0, 1) . "(?:" . substr($term, 1) . "s?)": "" ;},
  $terms)) . ")\s*";

$reg = "~$chapter_main_rx((\d+(?:\.\d+)?(?:[A-Z]\b)?)(?:\s*(?:[,&+-]|and)\s*(?:$chapter_aux_rx)?(?4))*)~ui";

foreach ($strs as $s) {
    if (preg_match($reg, $s, $m)) {
        $p3 = preg_replace_callback(
            "~(\d*(?:\.\d+)?)([A-Z]?)\s*-\s*(?:$chapter_aux_rx)?|(\d+(?:\.\d+)?(?:[A-Z]\b)?)(?:\s*(?:[,&+]|and)\s*(?:$chapter_aux_rx)?(?1))*~ui", function($x) use ($chapter_aux_rx) {
                return (isset($x[3]) && strlen($x[3])) ? buildNumChain(preg_split("~\s*(?:[,&+]|and)\s*(?:$chapter_aux_rx)?~ui", $x[0])) 
                : ((isset($x[1]) && strlen($x[1])) ? ($x[1] + 0) : "") . ((isset($x[2]) && strlen($x[2])) ? ord(strtolower($x[2])) - 96 : "") . "-";
            }, $m[3]);
        print_r(["original" => $s, "found_match" => trim($m[0]), "converted" => $m[1] . $p3]);
        echo "\n";
    } else {
    	echo "No match for '$s'!\n";
    
    }
}

function buildNumChain($arr) {
    $ret = "";
    $rngnum = "";
    for ($i=0; $i < count($arr); $i++) {
        $val = $arr[$i];
        $part = "";
        if (preg_match('~^(\d+(?:\.\d+)?)([A-Z]?)$~i', $val, $ms)) {
        	$val = $ms[1];
        	if (!empty($ms[2])) {
        		$part = ' part ' . (ord(strtolower($ms[2])) - 96);
        	}
        }
        $val = $val + 0;
        if (($i < count($arr) - 1) && $val == ($arr[$i+1] + 0) - 1) {
            if (empty($rngnum))  {
                $ret .= ($i == 0 ? "" : " & ") . $val;
            }
            $rngnum = $val;
        } else if (!empty($rngnum) || $i == count($arr)) {
            $ret .= '-' . $val;
            $rngnum = "";
        } else {
            $ret .= ($i == 0 ? "" : " & ") . $val . $part;
        }
    }
    return $ret;
}