franciscoda / reversedregex

Format a string so that it will match against a given PCRE

reversedregex

Format a string so that it will match against a given PCRE

Example usage

require 'ReversedRegex.php';
$parser = new RegexParser('^/blog/(?<post_id>\d+)/.+$');
$reversed = new ReversedRegex($parser->regex()); // parse regex & reverse it
echo $reversed->format([
  'post_id' => 15,     // can be formatted by name or with index 0
  1 => 'My post title' // '.+' requires formatting too
]);

> /blog/15/My post title

Which tokens need formatting

• Character classes: ., \w, \W, \d, \D, \s, \S, [abcdefg]
• Variable-length repetitions of literals and non-literals: base+, base*, base?, base{2,3}, base{2,}. Note that if base is not a literal, you should provide a single formatting parameter to satisfy both base and the repetition.
• Fixed-length repetitions of non-literals: base{4}. Same as above
• Reversed lookarounds: (?!abc), (?<!abc)

Output verification

There's no verification at all. Consider the regex in the 'Example usage' section and the following code:

echo $reversed->format(['post_id' => 'lol', 1 => '']);

> /blog/lol/

This will not match against the regex. You should use something like preg_match on the output if you need verification.

What works as intended

Groups, named groups, character classes, lookarounds, anchors, string literals and repetitions

What is not implemented

• Alternations (i.e. pipe operator): It is not possible to determine which side of the operation to format without further inspection of the involved argument counts, types and matching tokens.

$p = new RegexParser('\d+|[a-zA-Z]+');
$r = new ReversedRegex($p->regex());
$r->format(['hello']); // which one?

• Backreferences: There is not a 1:1 relation between groups and formatting placeholders in some cases. More specifically, PCRE dictates that when a group is repeated the backreference matches the last captured value of the group. However, we format both the group and the repetition with a single value. The problem gets increasingly difficult when the group contains variable-length repetitions.

$p = new RegexParser('(\d)+\1');
$r = new ReversedRegex($p->regex());
$r->format(['123']); // (\d)+ formatted as '123', but how to tell what is '\1'?