WP_Customize_Header_Image_Setting::sanitize_choice( mixed $value )

	private function sanitize_choice( $value ) {
		// Custom_Image_Header::set_header_image() accepts an object in place of an array.
		if ( is_object( $value ) ) {
			$value = (array) $value;
		}

		if ( is_string( $value ) ) {
			return sanitize_text_field( $value );
		}

		if ( ! is_array( $value ) ) {
			return null;
		}

		/*
		 * The sanitized value is assembled member by member rather than filtered down from the
		 * supplied one, so that nothing but the members below can end up in it.
		 */
		$sanitized = array();

		if ( isset( $value['attachment_id'] ) ) {
			if ( ! is_scalar( $value['attachment_id'] ) ) {
				return null;
			}
			$attachment_id = absint( $value['attachment_id'] );

			/*
			 * A supplied attachment must be an existing image, since its ID is written to postmeta and its
			 * data displayed. Note that an ID of zero must be skipped rather than looked up, as
			 * get_post_mime_type() falls back to the global post when passed an empty value.
			 */
			if ( $attachment_id > 0 ) {
				$mime_type = get_post_mime_type( $attachment_id );
				if ( ! is_string( $mime_type ) || ! str_starts_with( $mime_type, 'image/' ) ) {
					return null;
				}
			}

			$sanitized['attachment_id'] = $attachment_id;
		}

		if ( isset( $value['url'] ) ) {
			if ( ! is_string( $value['url'] ) ) {
				return null;
			}
			$sanitized['url'] = sanitize_url( $value['url'] );
			if ( '' === $sanitized['url'] ) {
				return new WP_Error( 'invalid_url', __( 'Invalid URL.' ) );
			}
		}

		if ( isset( $value['thumbnail_url'] ) ) {
			if ( ! is_string( $value['thumbnail_url'] ) ) {
				return null;
			}
			$sanitized['thumbnail_url'] = sanitize_url( $value['thumbnail_url'] );
			if ( '' === $sanitized['thumbnail_url'] ) {
				return new WP_Error( 'invalid_url', __( 'Invalid URL.' ) );
			}
		}

		if ( isset( $value['timestamp'] ) ) {
			if ( ! is_scalar( $value['timestamp'] ) ) {
				return null;
			}
			$sanitized['timestamp'] = absint( $value['timestamp'] );
		}

		if ( isset( $value['width'] ) ) {
			if ( ! is_scalar( $value['width'] ) ) {
				return null;
			}
			$sanitized['width'] = absint( $value['width'] );
		}

		if ( isset( $value['height'] ) ) {
			if ( ! is_scalar( $value['height'] ) ) {
				return null;
			}
			$sanitized['height'] = absint( $value['height'] );
		}

		if ( isset( $value['alt_text'] ) ) {
			if ( ! is_string( $value['alt_text'] ) ) {
				return null;
			}
			$sanitized['alt_text'] = sanitize_text_field( $value['alt_text'] );
		}

		if ( isset( $value['attachment_parent'] ) ) {
			if ( ! is_scalar( $value['attachment_parent'] ) ) {
				return null;
			}
			$sanitized['attachment_parent'] = absint( $value['attachment_parent'] );
		}

		return $sanitized;
	}