import type { Plugin } from "unified"
import { visit } from "unist-util-visit"

export type ExternalLinksOptions = {
	/**
	 * Predicate to decide whether a URL is external.
	 *
	 * Defaults to absolute http(s) URLs.
	 *
	 * @example
	 * (href) => href.startsWith("https://") && !href.includes("lix.dev")
	 */
	isExternal?: (href: string) => boolean
	/**
	 * Target attribute to apply to external links.
	 *
	 * @default "_blank"
	 */
	target?: string
	/**
	 * Rel attribute to apply to external links.
	 *
	 * @default "noopener noreferrer"
	 */
	rel?: string
}

/**
 * Remark plugin that annotates external links so `remark-rehype` emits `target` and `rel`.
 *
 * Intended to be used as an opt-in feature from `parse()` or `serializeToHtml()`.
 *
 * @example
 * unified().use(remarkExternalLinks, true)
 */
export const remarkExternalLinks: Plugin<[ExternalLinksOptions | boolean | undefined], any> = (
	options
) => {
	if (options === false) {
		return () => {}
	}

	const config: ExternalLinksOptions = typeof options === "object" && options != null ? options : {}

	const isExternal = config.isExternal ?? ((href: string) => /^https?:\/\//i.test(href))
	const target = config.target ?? "_blank"
	const rel = config.rel ?? "noopener noreferrer"

	return (tree: any) => {
		visit(tree, "link", (node: any) => {
			const url = node?.url
			if (typeof url !== "string") return
			if (!isExternal(url)) return

			const data = (node.data ||= {})
			const hProperties = (data.hProperties ||= {}) as Record<string, any>
			hProperties.target = target
			hProperties.rel = rel
		})
	}
}