adding string after every 'n' number of lines in a file using php - php

Question

I have a .lst(playlist) file with around 1800 lines of data. Each line contains a URL to an audio file that is being played on my radio station.
The thing is I need to add URLs to some Advertisements after every 'n' number of lines in that file.
There are 10 URLs of advertisements from which 1 URL needs to be added after every 5 lines.
Example: URLs of Advertisements are in this format: file1.mp3, file2.mp3 ... file10.mp3
They will be added like this: file1.mp3 on line 5, file2.mp3 on line 10, file3.mp3 on line 15 and so on. After file10.mp3 has been inserted, it will again start from file1.mp3. I hope you understand.
So far I have managed to cook up the following code, but it only takes up one string to be added and have to manually tell the line number on which the string will be added. Unable to figure out the looping logic to do the aforementioned work.
$url = "/home/station/content/file1.mp3";
$line_number = 5; //add above URL on line number 5
$contents = file('playlist.lst', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
if($line_number > sizeof($contents)) {
$line_number = sizeof($contents) + 1;
}
array_splice($contents, $line_number-1, 0, array($url));
$contents = implode("\n", $contents);
file_put_contents('playlist.lst', $contents);
How can I achieve this ?

Answer 1

You can use array_chunk to split your array into $line_number. Then, use array_map() to add your advertisements to each group. Finally, you could reduce to a linear array. You can format the $url using sprintf().
$url = "/home/station/content/file%d.mp3"; // use %d to use using sprintf()
$line_number = 5; //add above URL on line number 5
$counter = 1;
$contents = file('playlist.lst', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
// split in group of $line_number
$groups = array_chunk($contents, $line_number);
// for each group:
$groups = array_map(function($arr) use ($url, &$counter) { // pass $counter as reference
// format the link
$adv = sprintf($url, $counter++) ;
// restart to 1 if greater than 10
if ($counter > 10) $counter = 1;
// append to group
$arr[] = $adv;
return $arr ;
},$groups);
// transform to linear array
$contents = array_reduce($groups, 'array_merge', array());
// save new file
file_put_contents('playlist.lst', implode("\n", $contents));

Answer 2

You could do it this way, with a simple loop:
//changing it to a "model" string, we are going to add the correct file number later
$url = "/home/station/content/file";
$contents = file('playlist.lst', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$count = 0;
$AddCount = 1;
//Loop until there is nothing left in our radio list
while ($count < sizeof($contents)) {
//if we have a multiple of 5, we are inserting an ad
if (($count % 5) == 0) {
// to know wich ad to add we use our AddCounter
$tmp = $url . strval($AddCount) . ".mp3";
//As suggested by Justinas, don't forget that each time you had a line you need to also increase the index for the next one using $count%5 to know how many lines you already added
array_splice($contents, $count - 1 + ($count % 5) , 0, array($tmp));
$AddCount += 1;
if ($AddCount > 10)
$AddCount = 1;
}
$count += 1;
}
$contents = implode("\n", $contents);
file_put_contents('playlist.lst', $contents);
This way, you don't even have to handle the advertisements file selection yourself as long as they are all formated like you said.

Answer 3

You should do a loop in such way.
$line_number = 5;
$line_count = 0;
for($i=0; $i < sizeof($contents); $i++)
{
$line_count = $line_count +1; // start with Line 1 that +1
if($line_count == $line_number)
{
// do your magic code of adding a line
$line_count = 0; // refresh counting from the beginning
}
}

Answer 4

You don't need to handle each line in the file one at a time.
Leave the file contents as its original string, inject placeholders with regex, then replace those placeholders with your ad array strings.
Code: (Basic Demo)
$filename = 'playlist.lst';
file_put_contents(
$filename,
vsprintf(
preg_replace(
'/(?:.+(\R)){5}\K/', // match (and forget) 5 lines, capture the newline character
'%s\1', // inject the placeholder following the the newline character
file_get_contents($filename),
count($ads) // make the exact number of needed placeholders
),
$ads // replace the placeholders with the ad strings
)
);