[PHP] テキスト内のURLをリンクにする関数

linker.php

<?php

function linker($text = null ,$blank = false)
{
    if (empty($text)) {
        return null;
    }
    
    $text = preg_replace('/&apos;/', '&#39;', $text); // IE対策
    
    $pattern = '%([^<]+(?:(?!<a\b)<[^<]*)*|(?:(?!<a\b)<[^<]*)+)|(<a\b[^>]*>[^<]*(?:(?!</a\b)<[^<]*)*</a\s*>)%ix';
    return preg_replace_callback($pattern, function($m) use($text, $blank) {
        if (isset($m[2])) {
            return $m[2];
        } else {
            $pattern = '/(\() # $1 "(" start delimiter.
                    ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+) # $2: URL.
                    (\)) # $3: ")" end delimiter.
                    | # Alternative 2: URL delimited by [square brackets].
                    (\[) # $4: "[" start delimiter.
                    ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+) # $5: URL.
                    (\]) # $6: "]" end delimiter.
                    | # Alternative 3: URL delimited by {curly braces}.
                    (\{) # $7: "{" start delimiter.
                    ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+) # $8: URL.
                    (\}) # $9: "}" end delimiter.
                    | # Alternative 4: URL delimited by <angle brackets>.
                    (<|&(?:lt|\#60|\#x3c);) # $10: "<" start delimiter (or HTML entity).
                    ((?:ht|f)tps?:\/\/[a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]+) # $11: URL.
                    (>|&(?:gt|\#62|\#x3e);) # $12: ">" end delimiter (or HTML entity).
                    | # Alternative 5: URL not delimited by (), [], {} or <>.
                    ( # $13: Prefix proving URL not already linked.
                    (?: ^ # Can be a beginning of line or string, or
                    | [^=\s\'"\]] # a non-"=", non-quote, non-"]", followed by
                    ) \s*[\'"]? # optional whitespace and optional quote;
                    | [^=\s]\s+ # or... a non-equals sign followed by whitespace.
                    ) # End $13. Non-prelinkified-proof prefix.
                    ( \b # $14: Other non-delimited URL.
                    (?:ht|f)tps?:\/\/ # Required literal http, https, ftp or ftps prefix.
                    [a-z0-9\-._~!$\'()*+,;=:\/?#[\]@%]+ # All URI chars except "&" (normal*).
                    (?: # Either on a "&" or at the end of URI.
                    (?! # Allow a "&" char only if not start of an...
                    &(?:gt|\#0*62|\#x0*3e); # HTML ">" entity, or
                    | &(?:amp|apos|quot|\#0*3[49]|\#x0*2[27]); # a [&\'"] entity if
                    [.!&\',:?;]? # followed by optional punctuation then
                    (?:[^a-z0-9\-._~!$&\'()*+,;=:\/?#[\]@%]|$) # a non-URI char or EOS.
                    ) & # If neg-assertion true, match "&" (special).
                    [a-z0-9\-._~!$\'()*+,;=:\/?#[\]@%]* # More non-& URI chars (normal*).
                    )* # Unroll-the-loop (special normal*)*.
                    [a-z0-9\-_~$()*+=\/#[\]@%] # Last char can\'t be [.!&\',;:?]
                    ) # End $14. Other non-delimited URL.
                    /imx';
            $replace = '$1$4$7$10$13<a href="$2$5$8$11$14"'.($blank ? ' target="_blank"' : NULL).'>$2$5$8$11$14</a>$3$6$9$12';
            return preg_replace( $pattern, $replace, $text );
        }
    }, $text );
}