😈

TitleCaser.php

<?php

class TitleCaser
{
    protected static $smallWords = [
        '(?<!q&)a',
        'an',
        'and',
        'as',
        'at(?!&t)',
        'but',
        'by',
        'en',
        'for',
        'if',
        'in',
        'of',
        'on',
        'or',
        'the',
        'to',
        'v[.]?',
        'via',
        'vs[.]?',
    ];

    public static function toTitleCase($str)
    {
        $smallWordsRx = implode('|', self::$smallWords);

        $apostropheRx = '(?x: [\'’] [[:lower:]]* )?';

        $str = (new StrProxy($str))->trim();

        if (preg_match('/[[:lower:]]/', $str) === 0) {
            $str = $str->lower();
        }

        // The main substitutions
        $str = preg_replace_callback(
            '~\b (_*) (?:                                                         # 1. Leading underscore and
                        ( (?<=[ ][/\\\\]) [[:alpha:]]+ [-_[:alpha:]/\\\\]+ |              # 2. file path or 
                          [-_[:alpha:]]+ [@.:] [-_[:alpha:]@.:/]+ ' . $apostropheRx . ' ) #    URL, domain, or email
                        |
                        ( (?i: ' . $smallWordsRx . ' ) ' . $apostropheRx . ' )            # 3. or small word (case-insensitive)
                        |
                        ( [[:alpha:]] [[:lower:]\'’()\[\]{}]* ' . $apostropheRx . ' )     # 4. or word w/o internal caps
                        |
                        ( [[:alpha:]] [[:alpha:]\'’()\[\]{}]* ' . $apostropheRx . ' )     # 5. or some other word
                      ) (_*) \b                                                           # 6. With trailing underscore
                    ~ux',
            function ($matches) {
                // Preserve leading underscore
                $str = $matches[1];

                if ($matches[2]) {
                    // Preserve URLs, domains, emails and file paths
                    $str .= $matches[2];
                } elseif ($matches[3]) {
                    // Lower-case small words
                    $str .= (new StrProxy($matches[3]))->lower();
                } elseif ($matches[4]) {
                    // Capitalize word w/o internal caps
                    $str .= (new StrProxy($matches[4]))->capitalize();
                } else {
                    // Preserve other kinds of word (iPhone)
                    $str .= $matches[5];
                }

                // Preserve trailing underscore
                $str .= $matches[6];

                return $str;
            },
            $str);

        // Exceptions for small words: capitalize at start of title...
        $str = preg_replace_callback(
            '~(  \A [[:punct:]]*           # start of title...
                      |  [:.;?!][ ]+               # or of subsentence...
                      |  [ ][\'"“‘(\[][ ]* )       # or of inserted subphrase...
                      ( ' . $smallWordsRx . ' ) \b # ...followed by small word
                     ~uxi',
            function ($matches) {
                return $matches[1] . (new StrProxy($matches[2]))->capitalize();
            },
            $str
        );

        // ...and end of title
        $str = preg_replace_callback(
            '~\b ( ' . $smallWordsRx . ' ) # small word...
                      (?= [[:punct:]]* \Z          # ...at the end of the title...
                      |   [\'"’”)\]] [ ] )         # ...or of an inserted subphrase?
                     ~uxi',
            function ($matches) {
                return (new StrProxy($matches[1]))->capitalize();
            },
            $str
        );

        // Exceptions for small words in hyphenated compound words
        // e.g. "in-flight" -> In-Flight
        $str = preg_replace_callback(
            '~\b
                        (?<! -)                   # Negative lookbehind for a hyphen; we do not want to match man-in-the-middle but do want (in-flight)
                        ( ' . $smallWordsRx . ' )
                        (?= -[[:alpha:]]+)        # lookahead for "-someword"
                       ~uxi',
            function ($matches) {
                return (new StrProxy($matches[1]))->capitalize();
            },
            $str
        );

        // e.g. "Stand-in" -> "Stand-In" (Stand is already capped at this point)
        $str = preg_replace_callback(
            '~\b
                      (?<!…)                    # Negative lookbehind for a hyphen; we do not want to match man-in-the-middle but do want (stand-in)
                      ( [[:alpha:]]+- )         # $1 = first word and hyphen, should already be properly capped
                      ( ' . $smallWordsRx . ' ) # ...followed by small word
                      (?!	- )                 # Negative lookahead for another -
                     ~uxi',
            function ($matches) {
                return $matches[1] . (new StrProxy($matches[2]))->capitalize();
            },
            $str
        );

        return $str;
    }
}