utils.js

/** @param {import("@sveltejs/kit").RouteDefinition<any>} route */
export function get_pathname(route) {
	let i = 1;

	const pathname = route.segments
		.map((segment) => {
			if (!segment.dynamic) {
				return '/' + segment.content;
			}

			const parts = segment.content.split(/\[(.+?)\](?!\])/);
			let result = '';

			if (
				parts.length === 3 &&
				!parts[0] &&
				!parts[2] &&
				(parts[1].startsWith('...') || parts[1][0] === '[')
			) {
				// Special case: segment is a single optional or rest parameter.
				// In that case we don't prepend a slash (also see comment in pattern_to_src).
				result = `$${i++}`;
			} else {
				result =
					'/' +
					parts
						.map((content, j) => {
							if (j % 2) {
								return `$${i++}`;
							} else {
								return content;
							}
						})
						.join('');
			}

			return result;
		})
		.join('');

	return pathname[0] === '/' ? pathname.slice(1) : pathname;
}

/**
 * Adjusts the stringified route regex for Vercel's routing system
 * @param {string} pattern stringified route regex
 */
export function pattern_to_src(pattern) {
	let src = pattern
		// remove leading / and trailing $/
		.slice(1, -2)
		// replace escaped \/ with /
		.replace(/\\\//g, '/');

	// replace the root route "^/" with "^/?"
	if (src === '^/') {
		src = '^/?';
	}

	// Move non-capturing groups that swallow slashes into their following capturing groups.
	// This is necessary because during ISR we're using the regex to construct the __pathname
	// query parameter: In case of a route like [required]/[...rest] we need to turn them
	// into $1$2 and not $1/$2, because if [...rest] is empty, we don't want to have a trailing
	// slash in the __pathname query parameter which wasn't there in the original URL, as that
	// could result in a false trailing slash redirect in the SvelteKit runtime, leading to infinite redirects.
	src = src.replace(/\(\?:\/\((.+?)\)\)/g, '(/$1)');

	return src;
}