\WP_Stager_Integration\Calendar::calculate_timestamp_year_start(int $year): int

Full Code

/**
 * Calculates the start timestamp of a given year (00:00:00 in the current site's timezone, first day of the year).
 *
 * @param int $year     The year
 *
 * @return int   Unix timestamp
 */
public static function calculate_timestamp_year_start( $year ) {

    // Type casting
    $year = (int) $year;

    // Get first day of year timestamp
    return self::calculate_local_timestamp( sprintf( '%d-01-01 00:00:00', $year ) );
}