Export Script with batch processing using WP_FileSystem, streaming and buffering

export.php

global $wp_filesystem;

// If not already set, initialize the WP filesystem.
if ( empty( $wp_filesystem ) ) {
	require_once ABSPATH . '/wp-admin/includes/file.php';
	WP_Filesystem();
}

$uploads_dir = wp_get_upload_dir()['basedir'] . '/movie-library/';

if ( ! $wp_filesystem->is_dir( $uploads_dir ) ) {

	$wp_filesystem->mkdir( $uploads_dir );

}

$file_path = $uploads_dir . $file_name;

// If output file doesn't exists, create it.
if ( ! $wp_filesystem->exists( $file_path ) ) {

	$wp_filesystem->touch( $file_path );

}

ob_start();
$output_stream = fopen( 'php://output', 'w' );
fputcsv( $output_stream, $header_row );

forEach($batches as $batch) {
    $movie_data = get_movie_data();
    fputcsv( $output_stream, $movie_data );
}

fclose( $output_stream );

$wp_filesystem->put_contents( $file_path, ob_get_clean() );   // final IO