PHP: How do I sort strings which contain a date?

Using PHP 7.4 I have an array called $videoFiles which contains paths to video files like this

/www/nginx/html/camera1/today/event69-27062023_115101.mp4

The file name format is "event(event no)-(DDMMYY_HHMMSS).mp4"

I'm trying to sort this array so I have earliest first and latest last. I tried using this function to do what I need:

<?php

usort(
      $videoFiles,
      create_function(
         '$a,$b',
         'return filemtime($a) - filemtime($b);'
      )
   );

But this didn't give the right result. The files are still unsorted in the array. How do I get the sort done correctly?

PHP usort(array &$array, callable $callback): true needs a callback to a function that carries out the actual comparison.

To compare dates in your file names you first need to isolate the string that represents a date plus time, and then convert it to a DateTime object. Then a DateTime comparison can happen.

Here is the code sample:

    function extractDate($string){
        $dateString = substr($string, strrpos($string, '-') + 1, 15);
        return DateTime::createFromFormat('dmY_his', $dateString);
    }

     usort($files, function ($file1,$file2){

        $date1 = extractDate($file1);
        $date2 = extractDate($file2);

        if ($date1 == $date2) {
            return 0;
        }
        return ($date1 < $date2) ? -1 : 1;

    });

$files = [
    '/www/nginx/html/camera1/today/event120-27062023_115101.mp4',
    '/www/nginx/html/camera1/today/event120-27062023_113101.mp4',
    '/www/nginx/html/camera1/today/event69-27062023_115101.mp4',
    '/www/nginx/html/camera1/today/event69-27062023_113101.mp4'
];

usort($files, function ($a, $b) {
    $dateA = substr($a, strrpos($a, '-') + 1, 15);
    $dateB = substr($b, strrpos($b, '-') + 1, 15);

    $dateTimeA = DateTime::createFromFormat('dmY_His', $dateA);
    $dateTimeB = DateTime::createFromFormat('dmY_His', $dateB);

    return $dateTimeB <=> $dateTimeA;
});

// Output
Array
(
    [0] => /www/nginx/html/camera1/today/event120-27062023_115101.mp4
    [1] => /www/nginx/html/camera1/today/event69-27062023_115101.mp4
    [2] => /www/nginx/html/camera1/today/event120-27062023_113101.mp4
    [3] => /www/nginx/html/camera1/today/event69-27062023_113101.mp4
)

Try this one. It parses the timestamps, converts them into sort-ready format and compares them:

 $videoFiles = ['/www/nginx/html/camera1/today/event69-27062023_115101.mp4',
    '/www/nginx/html/camera1/today/event69-30062023_115101.mp4',
    '/www/nginx/html/camera1/today/event69-25062023_115101.mp4'
    ];

function getDateFromFilename($filename) {
    preg_match('/\d{8}\_\d{6}/',$filename,$matches);
    list($day,$time) = explode('_',$matches[0]);

    $dd = substr($day,0,2);
    $mm = substr($day,2,2);
    $yy = substr($day,4,4);

    return $yy.$mm.$dd.$time;
}

usort($videoFiles, function ($a,$b){

    $aTime = getDateFromFilename($a);
    $bTime = getDateFromFilename($b);
    if ($aTime > $bTime)  return 1;
    return -1;
});