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<?php
/**
source: http://php.net/manual/en/function.scandir.php
Thanks to gambit_642 AT hotmailDOTcom 4 years ago

Needed something that could return the contents of single or multiple directories, recursively or non-recursively,
for all files or specified file extensions that would be
accessible easily from any scope or script.

And I wanted to allow overloading cause sometimes I'm too lazy to pass all params.
*/
class scanDir {
    static private $directories, $files, $ext_filter, $recursive;

// ----------------------------------------------------------------------------------------------
    // scan(dirpath::string|array, extensions::string|array, recursive::true|false)
    static public function scan(){
        // Initialize defaults
        self::$recursive = false;
        self::$directories = array();
        self::$files = array();
        self::$ext_filter = false;

        // Check we have minimum parameters
        if(!$args = func_get_args()){
            die("Must provide a path string or array of path strings");
        }
        if(gettype($args[0]) != "string" && gettype($args[0]) != "array"){
            die("Must provide a path string or array of path strings");
        }

        // Check if recursive scan | default action: no sub-directories
        if(isset($args[2]) && $args[2] == true){self::$recursive = true;}

        // Was a filter on file extensions included? | default action: return all file types
        if(isset($args[1])){
            if(gettype($args[1]) == "array"){self::$ext_filter = array_map('strtolower', $args[1]);}
            else
            if(gettype($args[1]) == "string"){self::$ext_filter[] = strtolower($args[1]);}
        }

        // Grab path(s)
        self::verifyPaths($args[0]);
        return self::$files;
    }

    static private function verifyPaths($paths){
        $path_errors = array();
        if(gettype($paths) == "string"){$paths = array($paths);}

        foreach($paths as $path){
            if(is_dir($path)){
                self::$directories[] = $path;
                $dirContents = self::find_contents($path);
            } else {
                $path_errors[] = $path;
            }
        }

        if($path_errors){echo "The following directories do not exists<br />";die(var_dump($path_errors));}
    }

    // This is how we scan directories
    static private function find_contents($dir){
        $result = array();
        $root = scandir($dir);
        foreach($root as $value){
            if($value === '.' || $value === '..') {continue;}
            if(is_file($dir.DIRECTORY_SEPARATOR.$value)){
                if(!self::$ext_filter || in_array(strtolower(pathinfo($dir.DIRECTORY_SEPARATOR.$value, PATHINFO_EXTENSION)), self::$ext_filter)){
                    self::$files[] = $result[] = $dir.DIRECTORY_SEPARATOR.$value;
                }
                continue;
            }
            if(self::$recursive){
                foreach(self::find_contents($dir.DIRECTORY_SEPARATOR.$value) as $value) {
                    self::$files[] = $result[] = $value;
                }
            }
        }
        // Return required for recursive search
        return $result;
    }
}
?>

Usage:
scanDir::scan(path(s):string|array, [file_extensions:string|array], [subfolders?:true|false]);
<?php
//Scan a single directory for all files, no sub-directories
$files = scanDir::scan('D:\Websites\temp');

//Scan multiple directories for all files, no sub-dirs
$dirs = array(
    'D:\folder';
    'D:\folder2';
    'C:\Other';
);
$files = scanDir::scan($dirs);

// Scan multiple directories for files with provided file extension,
// no sub-dirs
$files = scanDir::scan($dirs, "jpg");
//or with an array of extensions
$file_ext = array(
    "jpg",
    "bmp",
    "png"
);
$files = scanDir::scan($dirs, $file_ext);

// Scan multiple directories for files with any extension,
// include files in recursive sub-folders
$files = scanDir::scan($dirs, false, true);

// Multiple dirs, with specified extensions, include sub-dir files
$files = scanDir::scan($dirs, $file_ext, true);
?>