wikimedia/mediawiki-extensions-Wikibase

<?php

namespace Wikibase\Lib\Units;

/**
 * JSON based unit conversion storage.
 * Storage format:
 * Json map, each element is 'Qsource': [ <factor>, 'QstandardUnit' ]
 * Example:
 * {
 * "Q103510": [ "100000", "Q44395" ],
 * "Q130964": [ "4.19", "Q25269" ],
 * "Q182429": [ "1", "Q182429" ]
 * }
 * Q182429 here is a primary unit since source and standard are the same.
 * Primary units must have factor of 1.
 * Another acceptable format is:
 * "Q103510": { "factor": "100000", "unit": "Q44395" },
 *
 * @license GPL-2.0-or-later
 * @author Stas Malyshev
 */
class JsonUnitStorage extends BaseUnitStorage {

    /**
     * Filename of the source file
     * @var string
     */
    private $sourceFile;

    /**
     * @param string $fileName Filename of the storage file.
     */
    public function __construct( $fileName ) {
        $this->sourceFile = $fileName;
    }

    /**
     * Load data from concrete storage
     * @return array[]|null
     */
    protected function loadStorageData() {
        if ( !is_readable( $this->sourceFile ) ) {
            return null;
        }
        $data = file_get_contents( $this->sourceFile );
        if ( !$data ) {
            return null;
        }
        return json_decode( $data, true );
    }

}