FileContentsHasher.php

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<?php
class FileContentsHasher {
    private const ALGO = 'md4';
 
    protected $cache;
 
    private static $instance;
 
    public function __construct() {
        $this->cache = function_exists( 'apcu_fetch' ) ? new APCUBagOStuff() : new EmptyBagOStuff();
    }
 
    public static function singleton() {
        if ( !self::$instance ) {
            self::$instance = new self;
        }
 
        return self::$instance;
    }
 
    private function getFileContentsHashInternal( $filePath ) {
        // phpcs:ignore Generic.PHP.NoSilencedErrors.Discouraged
        $mtime = @filemtime( $filePath );
        if ( $mtime === false ) {
            return false;
        }
 
        $cacheKey = $this->cache->makeGlobalKey( __CLASS__, $filePath, $mtime, self::ALGO );
        return $this->cache->getWithSetCallback(
            $cacheKey,
            $this->cache::TTL_DAY,
            static function () use ( $filePath ) {
                // phpcs:ignore Generic.PHP.NoSilencedErrors.Discouraged
                $contents = @file_get_contents( $filePath );
                if ( $contents === false ) {
                    // Don't cache false
                    return false;
                }
 
                return hash( self::ALGO, $contents );
            }
        );
    }
 
    public static function getFileContentsHash( $filePaths ) {
        $instance = self::singleton();
 
        if ( !is_array( $filePaths ) ) {
            $filePaths = (array)$filePaths;
        }
 
        if ( count( $filePaths ) === 1 ) {
            $hash = $instance->getFileContentsHashInternal( $filePaths[0] );
            return $hash;
        }
 
        sort( $filePaths );
        $hashes = [];
        foreach ( $filePaths as $filePath ) {
            $hashes[] = $instance->getFileContentsHashInternal( $filePath ) ?: '';
        }
 
        $hashes = implode( '', $hashes );
        return $hashes ? hash( self::ALGO, $hashes ) : false;
    }
}