php getting file name with extension using its first characters

Question

Huh, this is my first serious web project and for that moment i've got simply big enigma.

The deal is to get previous and next file extension using its first letters, for instance:

there's file 04.jpeg 05.gif 06.tiff we're currently reading 05.gif so we remove extension

and now its '05' so we add one so we get '06' and HOW TO GET THAT FILE EXTENSION?!?!?!

Details:

The problem is that i need to fix my image browser which works in two modes:

1. Comics browser

   [comics in folder looks like:

   page00.extension

   page01.extension

   (...)

   page09.extension

   page10.extension

   page11.extension ]

2. Single files browser

   [single files in folder looks like:

   01.extension

   02.extension

   03.extension

   (...)

   09.extension

   10.extension

   11.extension ]

[extension maybe jpg,jpeg,gif,png etc.]

Im getting current $extension and file name using $_GET var.

Here is some code - im working with bootstrap 3 framework:

Also im sorry that there's no comments but this isn't really complicated as it looks like

<?php

if($type == 2) {
$number = substr($clean, 4);
$nextnum = $number + 1;
$prevnum = $number - 1;


$prevpath = HOW TO GET IT WITH EXTENSION??
$nextpath = HOW TO GET IT WITH EXTENSION??
$nextext = '.' . substr(strrchr($prevpath,'.'),1);
$prevext = '.' . substr(strrchr($nextpath,'.'),1);


if ($nextnum >= 10) {
$next    = 'page' . $nextnum . $nextext;
} else {
$next    = 'page0' . $nextnum . $nextext; }

if ($prevnum >= 10) {
$prev    = 'page' . $prevnum . $prevext;
} else {
$prev    = 'page0' . $prevnum . $prevext; }

if ($clean === "page00") {
$prev = 'page00' . $extension; }

$count = 'page' . $x;
if ($clean === $count) {
$next = $count . $extension; }

} elseif($type == 3) {

$nextnum = $clean + 1;
$prevnum = $clean - 1;

$prevpath = HOW TO GET IT WITH EXTENSION?? <====== MY PROBLEM
$nextpath = HOW TO GET IT WITH EXTENSION?? <====== MY PROBLEM
$nextext = '.' . substr(strrchr($prevpath,'.'),1);
$prevext = '.' . substr(strrchr($nextpath,'.'),1);

if ($nextnum >= 10) {
$next = $nextnum . $nextext;
$prev = $prevnum . $prevext;
} else {
$next = '0' . $nextnum . $nextext;
$prev = '0' . $prevnum . $prevext; }

if ($clean === "01") {
$prev = '01' . $extension; }

if ($clean === $x) {
$next = $x . $extension; } }


echo '<br />
<div class="btn-group btn-group-justified">
      <a class="btn btn-default" href="?browse=' . $prev . '" role="button">Poprzedni</a>
      <a class="btn btn-default" href="' . $goback . '" role="button">Wyjdź</a>
      <a class="btn btn-default" href="?browse=' . $next . '" role="button">Następny</a>
</div>';

?>

Answer 1

function get_next_file($file){
    $maxdigits = 2; // assuming the file always ends with two digits

    $dir = dirname($file) . DIRECTORY_SEPARATOR;
    $fname = pathinfo($file, PATHINFO_FILENAME);
    $name = substr($fname, 0, -$maxdigits);
    $digits = substr($fname, -$maxdigits) + 1;
    foreach(array('bmp', 'png', 'jpg', 'gif') as $ext){
        $test = $dir . $name . str_pad($digits, $maxdigits, '0', STR_PAD_LEFT) . '.' . $ext;
        if(file_exists($ext))return $ext;
    }
    return false; // no such file...
}

The complete function would look like the one above (not tested!). You would call it like so:

Assuming we have these files:

test01.png
test02.gif
test05.bmp

You get these results:

get_next_file('test01.png') => 'test02.gif'
get_next_file('test02.gif') => false        // 'coz the other file is not consecutive
get_next_file('test05.bmp') => false        // no other files to look for...

Answer 2

If you know the name of current file then you can search for files in a directory using glob:

if (is_array(glob('05.*'))) { /* do some stuff */ }

Else you can create a whilte-list of extensions and use file_exists:

foreach (array('jpg', 'jpeg', 'png') as $ext)
    if (file_exists('05.'. $ext)) { /* do some stuff */ }