FileStatePredicates.php

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<?php
class FileStatePredicates {
    protected const EXISTS = 'exists';
    protected const SIZE = 'size';
    protected const SHA1 = 'sha1';
 
    private $fileStateByPath;
 
    public function __construct() {
        $this->fileStateByPath = [];
    }
 
    public function assumeFileExists( string $path, $size, $sha1Base36 ) {
        $this->fileStateByPath[$path] = [
            self::EXISTS => true,
            self::SIZE => $size,
            self::SHA1 => $sha1Base36
        ];
    }
 
    public function assumeFileDoesNotExist( string $path ) {
        $this->fileStateByPath[$path] = [
            self::EXISTS => false,
            self::SIZE => false,
            self::SHA1 => false
        ];
    }
 
    public function resolveFileExistence( string $path, $curExistenceFunc ) {
        return self::resolveFileProperty( $path, self::EXISTS, $curExistenceFunc );
    }
 
    public function resolveFileSize( string $path, $curSizeFunc ) {
        return self::resolveFileProperty( $path, self::SIZE, $curSizeFunc );
    }
 
    public function resolveFileSha1Base36( string $path, $curSha1Func ) {
        return self::resolveFileProperty( $path, self::SHA1, $curSha1Func );
    }
 
    private function resolveFileProperty( $path, $property, $curValueFunc ) {
        if ( isset( $this->fileStateByPath[$path] ) ) {
            // File is predicated to have a counterfactual state
            $value = $this->fileStateByPath[$path][$property];
            if ( $value instanceof Closure ) {
                $value = $value();
                $this->fileStateByPath[$path][$property] = $value;
            }
        } else {
            // File is not predicated to have a counterfactual state; use the current state
            $value = $curValueFunc( $path );
        }
 
        return $value;
    }
 
    public function snapshot( array $paths ) {
        $snapshot = new self();
        foreach ( $paths as $path ) {
            if ( isset( $this->fileStateByPath[$path] ) ) {
                $snapshot->fileStateByPath[$path] = $this->fileStateByPath[$path];
            }
        }
 
        return $snapshot;
    }
}