Move directories in which all the MKV and MP4 video files have only one hard link, designed for Unraid

mover.php

#!/usr/bin/php
<?php

$source = '/mnt/cache/share';
$destination = '/mnt/disk1/share';
$threshold = 80;

if( ! @file_exists( $source ) ) {
	echo "Bad source directory\n";
	exit( 1 );
};

if( ! @file_exists( $destination ) ) {
	echo "Bad destination directory\n";
	exit( 1 );
};

if( parse_ini_file( '/var/local/emhttp/var.ini' )[ 'mdResyncPos' ] ) {
	echo "Parity check or rebuild running. Exiting, for safety.\n";
	exit( 2 );
};

function getFolderTree( $root, $dir = '' ) {
	$tree = [];
	foreach( array_diff( scandir( "$root$dir" ), [ '.', '..' ] ) as $name ) {
		if( is_dir( "$root$dir/$name" ) )
			$tree = array_merge( $tree, getFolderTree( $root, "$dir/$name" ) );
		elseif( is_file( "$root$dir/$name" ) )
			$tree[] = "$dir/$name";
		else {
			echo "This is neither a file, nor a directory: $root$dir/$name\n";
			exit( 1 );
		};
	};
	return $tree;
};

function getSourceTree( $root, $dir = '' ) {
	return array_map( function( $file ) use ( $root ) {
		$stat = stat( "$root/$file" );
		return [ 'node' => explode( '/', $file )[ 1 ], 'nlink' => $stat[ 'nlink' ], 'mtime' => $stat[ 'mtime' ] ];
	}, array_filter( getFolderTree( $root ), function( $file ) {
		return substr( $file, -4 ) === '.mkv' || substr( $file, -4 ) === '.mp4';
	} ) );
};

function sortSourceTree( $tree ) {
	usort( $tree, function( $a, $b ) {
		if( $a[ 'nlink' ] > $b[ 'nlink' ] )
			return -1;
		if( $a[ 'nlink' ] < $b[ 'nlink' ] )
			return 1;
		if( $a[ 'mtime' ] > $b[ 'mtime' ] )
			return 1;
		if( $a[ 'mtime' ] < $b[ 'mtime' ] )
			return -1;
		return 0;
	} );
	return $tree;
};

function filterSourceTree( $tree ) {
	for( $i = count( $tree ) - 1; $i >= 0; $i-- ) {
		for( $j = $i - 1; $j >= 0; $j-- ) {
			if( $tree[ $i ][ 'node' ] === $tree[ $j ][ 'node' ] ) {
				unset( $tree[ $i ] );
				continue 2;
			};
		};
		if( $tree[ $i ][ 'nlink' ] > 1 ) {
			unset( $tree[ $i ] );
		};
	};
	return $tree;
};

function usage( $source ) {
	return ( disk_total_space( $source ) - disk_free_space( $source ) ) / disk_total_space( $source ) * 100;
};

$tree = filterSourceTree( sortSourceTree( getSourceTree( $source ) ) );

while( ( $usage = usage( $source ) ) > $threshold && count( $tree ) > 0 ) {
	$next = array_shift( $tree );
	echo "Copying: $source/{$next[ 'node' ]} -> $destination/{$next[ 'node' ]}\n";
	exec( 'cp -a ' . escapeshellarg( "$source/{$next[ 'node' ]}" ) . ' ' . escapeshellarg( "$destination/{$next[ 'node' ]}" ), $out, $status );
	if( $status === 0 ) {
		echo "Copy successful. Removing: $source/{$next[ 'node' ]}\n";
		exec( 'rm -r ' . escapeshellarg( "$source/{$next[ 'node' ]}" ), $out, $status );
		if( $status === 0 ) {
			echo "Remove successful. Moving on.\n";
		}
		else {
			echo "Remove failed! Files exist in two places now. Oops. Moving on.\n";
		};
	}
	else {
		echo "Copying failed! Skipping remove, and moving on.\n";
	};
};

if( $usage > $threshold ) {
	echo "Your disk is ", ceil( $usage ), "% full, but there is nothing left to move.\n";
	exit( 2 );
};

echo "Your disk is down to ", ceil( $usage ), "% full.\n";