generate-permalink.js

import slugify from '@sindresorhus/slugify';

/**
 * @param  {object} data - The data object for the current collection item.
 * @param  {string} collectionType - The collection type.
 * @param  {string} collectionSlug - A localized, URL-safe slug for the collection type, used in the generated permalink.
 * @param  {string} paginationSlug - A localized, URL-safe slug for paginated URLs such as /page/2, used in the generated permalink.
 * @returns {string} - The generated permalink.
 */
export default function generatePermalink(data, collectionType, collectionSlug, paginationSlug = 'page') {
	/*
	If this post is a "stub" with no localized title, we assume it does not exist and prevent it from building.
	*/
	if (!Object.hasOwn(data, 'title')) {
		return false;
	}

	const lang = data.lang || data.defaultLanguage;
	const langSlug = data.supportedLanguages[lang].slug || lang;
	collectionSlug ||= collectionType;

	if (collectionType === 'pages') {
		/*
		If the page is a 404 page, return 404.html, optionally prepended with the language code.
		*/
		if (data.page.fileSlug === '404') {
			return (lang === data.defaultLanguage) ? '/404.html' : `/${langSlug}/404.html`;
		}

		/**
		If the page is the index page, the base path, optionally prepended with the language code.
		 */
		if (data.page.fileSlug === lang || data.page.inputPath.endsWith('index.md')) {
			return (lang === data.defaultLanguage) ? '/' : `/${langSlug}/`;
		}

		/*
		If the page is not the index page, return the page title in a URL-safe format, optionally prepended with the language code.
		*/
		const slug = data.slug || slugify(data.title, { decamelize: false });
		if (Object.hasOwn(data, 'pagination') && data.pagination.pageNumber > 0) {
			return (lang === data.defaultLanguage) ? `/${slug}/${paginationSlug}/${data.pagination.pageNumber + 1}/` : `/${langSlug}/${slug}/${paginationSlug}/${data.pagination.pageNumber + 1}/`;
		}

		return lang === data.defaultLanguage ? `/${slug}/` : `/${langSlug}/${slug}/`;
	}

	const slug = data.slug || slugify(data.title, { decamelize: false });
	return lang === data.defaultLanguage ? `/${collectionSlug}/${slug}/` : `/${langSlug}/${collectionSlug}/${slug}/`;
}