use preg_split to split chords and words - php

Question

I'm working on a little piece of code playing handling song tabs, but i'm stuck on a problem.
I need to parse each song tab line and to split it to get chunks of chords on the one hand, and words in the other.
Each chunk would be like :
$line_chunk = array(
0 => //part of line containing one or several chords
1 => //part of line containing words
);
They should stay "grouped". I mean by this that it should split only when the function reaches the "limit" between chords and words.
I guess I should use preg_split to achieve this. I made some tests, but I've been only able to split on chords, not "groups" of chords:
$line_chunks = preg_split('/(\[[^]]*\])/', $line, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
Those examples shows you what I would like to get :
on a line containing no chords :
$input = '{intro}';
$results = array(
array(
0 => null,
1 => '{intro}
)
);
on a line containing only chords :
$input = '[C#] [Fm] [C#] [Fm] [C#] [Fm]';
$results = array(
array(
0 => '[C#] [Fm] [C#] [Fm] [C#] [Fm]',
1 => null
)
);
on a line containing both :
$input = '[C#]I’m looking for [Fm]you [G#]';
$results = array(
array(
0 => '[C#]',
1 => 'I’m looking for'
),
array(
0 => '[Fm]',
1 => 'you '
),
array(
0 => '[G#]',
1 => null
),
);
Any ideas of how to do this ?
Thanks !

Answer 1

preg_split isn't the way to go. Most of the time, when you have a complicated split task to achieve, it's more easy to try to match what you are interested by instead of trying to split with a not easy to define separator.
A preg_match_all approach:
$pattern = '~ \h*
(?| # open a "branch reset group"
( \[ [^]]+ ] (?: \h* \[ [^]]+ ] )*+ ) # one or more chords in capture group 1
\h*
( [^[\n]* (?<=\S) ) # eventual lyrics (group 2)
| # OR
() # no chords (group 1)
( [^[\n]* [^\s[] ) # lyrics (group 2)
) # close the "branch reset group"
~x';
if (preg_match_all($pattern, $input, $matches, PREG_SET_ORDER)) {
$result = array_map(function($i) { return [$i[1], $i[2]]; }, $matches);
print_r($result);
}
demo
A branch reset group preserves the same group numbering for each branch.
Note: feel free to add:
if (empty($i[1])) $i[1] = null;
if (empty($i[2])) $i[2] = null;
in the map function if you want to obtain null items instead of empty items.
Note2: if you work line by line, you can remove the \n from the pattern.

Answer 2

I would go with PHP explode:
/*
* Process data
*/
$input = '[C#]I’m looking for [Fm]you [G#]';
$parts = explode("[", $input);
$results = array();
foreach ($parts as $item)
{
$pieces = explode("]", $item);
if (count($pieces) < 2)
{
$arrayitem = array( "Chord" => $pieces[0],
"Lyric" => "");
}
else
{
$arrayitem = array( "Chord" => $pieces[0],
"Lyric" => $pieces[1]);
}
$results[] = $arrayitem;
}
/*
* Echo results
*/
foreach ($results as $str)
{
echo "Chord: " . $str["Chord"];
echo "Lyric: " . $str["Lyric"];
}
Boudaries are not tested in the code, as well as remaining whitespaces, but it is a base to work on.