delete-thumbnails.php

<?php
public function delete_thumbnails( $args, $assoc_args ) {
		global $wpdb;

		if ( isset( $assoc_args['dry-run'] ) && 'false' === $assoc_args['dry-run'] ) {
			$dry_run = false;
		} else {
			$dry_run = true;
			WP_CLI::line( '!!! Doing a dry-run, no thumbnails will be deleted.' );
		}
		$total_rows = 0;

		$cache_key        = 'full-size-images-hash-' . get_option( 'template' );
		$full_size_images = wp_cache_get( $cache_key );

		if ( false === $full_size_images ) {
			$full_size_images = [];
			$result           = $wpdb->get_results( "SELECT meta_value FROM $wpdb->postmeta WHERE meta_key='_wp_attachment_metadata'" ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.PreparedSQLPlaceholders.UnnecessaryPrepare

			foreach ( $result as $row ) {
				$data = unserialize( $row->meta_value ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
				if ( ! isset( $data['file'] ) ) {
					continue;
				}
				$file_path                      = $data['file'];
				$full_size_images[ $file_path ] = 1;
			}

			wp_cache_set( $cache_key, $full_size_images, false, 300 );
		}

		$uploads_directory = wp_get_upload_dir()['basedir'];

		$years = array_diff( scandir( $uploads_directory ), [ '..', '.', '.DS_Store' ] );
		foreach ( $years as $year ) {

			// skip unknown folders
			if ( ! is_numeric( $year ) ) {
				continue;
			}

			$year_directory = $uploads_directory . '/' . $year;

			foreach ( [ '01', '02', '03', '04', '05', '06', '07', '08', '09', '10', '11', '12' ] as $month ) {
				$month_directory = $year_directory . '/' . $month;

				// not all months have uploads
				if ( ! file_exists( $month_directory ) ) {
					continue;
				}

				$images = array_diff( scandir( $month_directory ), [ '..', '.', '.DS_Store' ] );
				foreach ( $images as $image ) {
					$path      = $year . '/' . $month . '/' . $image;
					$full_path = $month_directory . '/' . $image;

					if ( ! isset( $full_size_images[ $path ] ) ) {
						$total_rows++;
						if ( ! $dry_run ) {
							WP_CLI::line( "Deleting $full_path" );
							unlink( $full_path ); // phpcs:ignore WordPressVIPMinimum.Functions.RestrictedFunctions.file_ops_unlink
						} else {
							WP_CLI::line( "Found: $full_path" );
						}
					}
				}
			}
		}

		// Print a success message
		if ( $total_rows ) {
			if ( $dry_run ) {
				WP_CLI::success( "Done. Found $total_rows files." );
			} else {
				WP_CLI::success( "Done. Deleted $total_rows files." );
			}
		} else {
			WP_CLI::success( 'Done. No files needed deleting.' );
		}
	}