wp_generate_attachment_metadata( int $attachment_id, string $file )

function wp_generate_attachment_metadata( $attachment_id, $file ) {
	$attachment = get_post( $attachment_id );

	$metadata = array();
	$support = false;
	$mime_type = get_post_mime_type( $attachment );

	if ( preg_match( '!^image/!', $mime_type ) && file_is_displayable_image( $file ) ) {
		$imagesize = getimagesize( $file );
		$metadata['width'] = $imagesize[0];
		$metadata['height'] = $imagesize[1];

		// Make the file path relative to the upload dir.
		$metadata['file'] = _wp_relative_upload_path($file);

		// Make thumbnails and other intermediate sizes.
		$_wp_additional_image_sizes = wp_get_additional_image_sizes();

		$sizes = array();
		foreach ( get_intermediate_image_sizes() as $s ) {
			$sizes[$s] = array( 'width' => '', 'height' => '', 'crop' => false );
			if ( isset( $_wp_additional_image_sizes[$s]['width'] ) ) {
				// For theme-added sizes
				$sizes[$s]['width'] = intval( $_wp_additional_image_sizes[$s]['width'] );
			} else {
				// For default sizes set in options
				$sizes[$s]['width'] = get_option( "{$s}_size_w" );
			}

			if ( isset( $_wp_additional_image_sizes[$s]['height'] ) ) {
				// For theme-added sizes
				$sizes[$s]['height'] = intval( $_wp_additional_image_sizes[$s]['height'] );
			} else {
				// For default sizes set in options
				$sizes[$s]['height'] = get_option( "{$s}_size_h" );
			}

			if ( isset( $_wp_additional_image_sizes[$s]['crop'] ) ) {
				// For theme-added sizes
				$sizes[$s]['crop'] = $_wp_additional_image_sizes[$s]['crop'];
			} else {
				// For default sizes set in options
				$sizes[$s]['crop'] = get_option( "{$s}_crop" );
			}
		}

		/**
		 * Filters the image sizes automatically generated when uploading an image.
		 *
		 * @since WP-2.9.0
		 * @since WP-4.4.0 Added the `$metadata` argument.
		 *
		 * @param array $sizes    An associative array of image sizes.
		 * @param array $metadata An associative array of image metadata: width, height, file.
		 */
		$sizes = apply_filters( 'intermediate_image_sizes_advanced', $sizes, $metadata );

		if ( $sizes ) {
			$editor = wp_get_image_editor( $file );

			if ( ! is_wp_error( $editor ) )
				$metadata['sizes'] = $editor->multi_resize( $sizes );
		} else {
			$metadata['sizes'] = array();
		}

		// Fetch additional metadata from EXIF/IPTC.
		$image_meta = wp_read_image_metadata( $file );
		if ( $image_meta )
			$metadata['image_meta'] = $image_meta;

	} elseif ( wp_attachment_is( 'video', $attachment ) ) {
		$metadata = wp_read_video_metadata( $file );
		$support = current_theme_supports( 'post-thumbnails', 'attachment:video' ) || post_type_supports( 'attachment:video', 'thumbnail' );
	} elseif ( wp_attachment_is( 'audio', $attachment ) ) {
		$metadata = wp_read_audio_metadata( $file );
		$support = current_theme_supports( 'post-thumbnails', 'attachment:audio' ) || post_type_supports( 'attachment:audio', 'thumbnail' );
	}

	if ( $support && ! empty( $metadata['image']['data'] ) ) {
		// Check for existing cover.
		$hash = md5( $metadata['image']['data'] );
		$posts = get_posts( array(
			'fields' => 'ids',
			'post_type' => 'attachment',
			'post_mime_type' => $metadata['image']['mime'],
			'post_status' => 'inherit',
			'posts_per_page' => 1,
			'meta_key' => '_cover_hash',
			'meta_value' => $hash
		) );
		$exists = reset( $posts );

		if ( ! empty( $exists ) ) {
			update_post_meta( $attachment_id, '_thumbnail_id', $exists );
		} else {
			$ext = '.jpg';
			switch ( $metadata['image']['mime'] ) {
			case 'image/gif':
				$ext = '.gif';
				break;
			case 'image/png':
				$ext = '.png';
				break;
			}
			$basename = str_replace( '.', '-', basename( $file ) ) . '-image' . $ext;
			$uploaded = wp_upload_bits( $basename, '', $metadata['image']['data'] );
			if ( false === $uploaded['error'] ) {
				$image_attachment = array(
					'post_mime_type' => $metadata['image']['mime'],
					'post_type' => 'attachment',
					'post_content' => '',
				);
				/**
				 * Filters the parameters for the attachment thumbnail creation.
				 *
				 * @since WP-3.9.0
				 *
				 * @param array $image_attachment An array of parameters to create the thumbnail.
				 * @param array $metadata         Current attachment metadata.
				 * @param array $uploaded         An array containing the thumbnail path and url.
				 */
				$image_attachment = apply_filters( 'attachment_thumbnail_args', $image_attachment, $metadata, $uploaded );

				$sub_attachment_id = wp_insert_attachment( $image_attachment, $uploaded['file'] );
				add_post_meta( $sub_attachment_id, '_cover_hash', $hash );
				$attach_data = wp_generate_attachment_metadata( $sub_attachment_id, $uploaded['file'] );
				wp_update_attachment_metadata( $sub_attachment_id, $attach_data );
				update_post_meta( $attachment_id, '_thumbnail_id', $sub_attachment_id );
			}
		}
	}
	// Try to create image thumbnails for PDFs
	else if ( 'application/pdf' === $mime_type ) {
		$fallback_sizes = array(
			'thumbnail',
			'medium',
			'large',
		);

		/**
		 * Filters the image sizes generated for non-image mime types.
		 *
		 * @since WP-4.7.0
		 *
		 * @param array $fallback_sizes An array of image size names.
		 * @param array $metadata       Current attachment metadata.
		 */
		$fallback_sizes = apply_filters( 'fallback_intermediate_image_sizes', $fallback_sizes, $metadata );

		$sizes = array();
		$_wp_additional_image_sizes = wp_get_additional_image_sizes();

		foreach ( $fallback_sizes as $s ) {
			if ( isset( $_wp_additional_image_sizes[ $s ]['width'] ) ) {
				$sizes[ $s ]['width'] = intval( $_wp_additional_image_sizes[ $s ]['width'] );
			} else {
				$sizes[ $s ]['width'] = get_option( "{$s}_size_w" );
			}

			if ( isset( $_wp_additional_image_sizes[ $s ]['height'] ) ) {
				$sizes[ $s ]['height'] = intval( $_wp_additional_image_sizes[ $s ]['height'] );
			} else {
				$sizes[ $s ]['height'] = get_option( "{$s}_size_h" );
			}

			if ( isset( $_wp_additional_image_sizes[ $s ]['crop'] ) ) {
				$sizes[ $s ]['crop'] = $_wp_additional_image_sizes[ $s ]['crop'];
			} else {
				// Force thumbnails to be soft crops.
				if ( 'thumbnail' !== $s ) {
					$sizes[ $s ]['crop'] = get_option( "{$s}_crop" );
				}
			}
		}

		// Only load PDFs in an image editor if we're processing sizes.
		if ( ! empty( $sizes ) ) {
			$editor = wp_get_image_editor( $file );

			if ( ! is_wp_error( $editor ) ) { // No support for this type of file
				/*
				 * PDFs may have the same file filename as JPEGs.
				 * Ensure the PDF preview image does not overwrite any JPEG images that already exist.
				 */
				$dirname = dirname( $file ) . '/';
				$ext = '.' . pathinfo( $file, PATHINFO_EXTENSION );
				$preview_file = $dirname . wp_unique_filename( $dirname, wp_basename( $file, $ext ) . '-pdf.jpg' );

				$uploaded = $editor->save( $preview_file, 'image/jpeg' );
				unset( $editor );

				// Resize based on the full size image, rather than the source.
				if ( ! is_wp_error( $uploaded ) ) {
					$editor = wp_get_image_editor( $uploaded['path'] );
					unset( $uploaded['path'] );

					if ( ! is_wp_error( $editor ) ) {
						$metadata['sizes'] = $editor->multi_resize( $sizes );
						$metadata['sizes']['full'] = $uploaded;
					}
				}
			}
		}
	}

	// Remove the blob of binary data from the array.
	if ( $metadata ) {
		unset( $metadata['image']['data'] );
	}

	/**
	 * Filters the generated attachment meta data.
	 *
	 * @since WP-2.1.0
	 *
	 * @param array $metadata      An array of attachment meta data.
	 * @param int   $attachment_id Current attachment ID.
	 */
	return apply_filters( 'wp_generate_attachment_metadata', $metadata, $attachment_id );
}