How to unwrap multiple multi-line text to single lines? - php

Question

I have data that looks like this:
#1
(1) This is a test.
a) This is a subtest one.
b) And another one.
(2) A really cool test.
(3) Here is the problem, text for each numbered line is
supposed to be on a single line like in (1) and (2), but
the text often spans multiple lines of text.
(4) How can I match the multi-line entries and unwrap them to single lines?
#2
(1) This is a test.
a) This is a subtest one.
b) And another one.
(2) A really cool test.
(3) Here is the problem, text for each numbered line is
supposed to be on a single line like in (1) and (2), but
the text often spans multiple lines of text.
(4) How can I match the multi-line entries and unwrap them to single lines?
#3
(1) This is a test.
a) This is a subtest one.
b) And another one.
(2) A really cool test.
(3) Here is the problem, text for each numbered line is
supposed to be on a single line like in (1) and (2), but
the text often spans multiple lines of text.
(4) How can I match the multi-line entries and unwrap them to single lines?
I need a Regular Expression that matches multiple multi-line text entries so I can unwrap them to single lines.
I've tried this:
$pattern = '/^(\(?[a-z0-9]+\) )([\s\S]+?(?!#))(^\(?[a-z0-9]+\))/mS';
$text = preg_replace_callback ($pattern, function ($grp) {
return $grp[1] . unwrap ($grp[2]) . PHP_EOL . $grp[3];
}, $text);
I feel like this should be a simple regex to write, but I'm having trouble for some reason.

Answer 1

You can match every entry using lookahead with the following regex and unwrap the whole match:
'^\(\d+\)[^#]*?(?=\n\(\d\)|\Z|#)'
See Demo
EDIT: from your question it's not clear how you want to handle sub-entries like a) and b). In this case they will be recognized as normal text.
EDIT2: in order to match a) and b) as entries as well:
'^(?:[a-z]\)|\(\d+\))[^#]*?(?=\n\(\d\)|\Z|#|\n[a-z]\))'
Demo

Answer 2

I would use preg_split with this pattern:
~(\R+|^#\d+$)+(?=\(\d+\)|[a-z]\)|\z)~m
The idea consists to describe what are the delimiters between the target parts:
at least one or more newlines followed with a target item or the end of the string
an eventual line with this format: #number
$res = preg_split('~(\R+|^#\d+$)+(?=\(\d+\)|[a-z]\)|\z)~m', $str, -1, PREG_SPLIT_NO_EMPTY);
demo
This is a bit shorter and more efficient than a preg_match_all approach and if you want to make it more flexible, you can add optional horizontal spaces in the pattern.
Note also that the pattern contains a capture group. The capture is totally useless, if you want you can change it to a non-capture group, but if you feel like a rebel and an adventurer, you can also begin the pattern with (?n) starting with PHP 7.3. With this modifier, capture groups are seen as non-capturing groups.