link: refactor href rewrite

- uses prop instead of attempting to read env variable
- uses URL type instead of custom heuristics

src/lib/Link.svelte

@@ -1,30 +1,43 @@
 <script lang="ts" module>
-	import { env } from '$env/dynamic/public';
+	/**
+	 * Rewrites the href based on a given basepath.
+	 * If the href is absolute, it is returned as is.
+	 * If the href is relative, the basepath is prepended.
+	 * @param href The original href.
+	 * @returns The rewritten href.
+	 */
+	export const rewriteHref = (href: string, basepath?: string | null): string => {
+		// If no base path is set, return the href as is
+		if (!basepath) return href;
 
-	const { PUBLIC_BASEPATH } = env;
-
-	const trim = (str: string, char: string, trimStart?: boolean, trimEnd?: boolean) => {
-		let start = 0,
-			end = str.length;
-
-		if (trimStart || trimStart === undefined) {
-			while (start < end && str[start] === char) start++;
+		// Use URL API to determine if href is relative or absolute
+		try {
+			// this will only succeed if href is absolute
+			const independentUrl = new URL(href);
+			return independentUrl.toString();
+		} catch {
+			// now we can assume that href is relative or entirely invalid
+			// test with a generic baseURI to see if it's valid relative
+			try {
+				const relativeUrl = new URL(href, 'http://example.com');
+				// if we reach here, it's a valid relative URL
+				const prefix = trimEdges(basepath, '/');
+				return `/${prefix}/${trimEdges(relativeUrl.pathname, '/', true, false)}`;
+			} catch {
+				throw new Error(`Attempted to rewrite invalid href: ${href}`);
+			}
 		}
-
-		if (trimEnd || trimEnd === undefined) {
-			while (end > start && str[end - 1] === char) end--;
-		}
-
-		return str.substring(start, end);
 	};
 </script>
 
 <script lang="ts">
 	import type { Snippet } from 'svelte';
 	import type { ClassValue, MouseEventHandler } from 'svelte/elements';
+	import { trimEdges } from './util';
 
 	interface Props {
 		href: string;
+		basepath?: string | null;
 		disabled?: boolean;
 		tab?: 'current' | 'new';
 		class?: ClassValue | null | undefined;
@@ -34,6 +47,7 @@
 
 	let {
 		href,
+		basepath,
 		disabled = false,
 		tab = 'current',
 		class: classValue,
@@ -41,10 +55,7 @@
 		onclick
 	}: Props = $props();
 
-	if (PUBLIC_BASEPATH && !href.startsWith('http://') && !href.startsWith('https://')) {
-		let prefix = trim(PUBLIC_BASEPATH, '/');
-		href = `/${prefix}/${trim(href, '/', true, false)}`;
-	}
+	const computedHref = $derived(rewriteHref(href, basepath));
 </script>
 
 <a
@@ -53,7 +64,7 @@
 		disabled && 'pointer-events-none cursor-not-allowed opacity-50',
 		classValue
 	]}
-	{href}
+	href={computedHref}
 	target={tab === 'new' ? '_blank' : undefined}
 	rel={tab === 'new' ? 'noopener noreferrer' : undefined}
 	{onclick}

src/lib/index.ts

@@ -18,7 +18,7 @@ export { default as InjectGoogleMaps } from './InjectGoogleMaps.svelte';
 export { default as InjectUmami } from './InjectUmami.svelte';
 export { default as InputGroup } from './InputGroup.svelte';
 export { default as Label } from './Label.svelte';
-export { default as Link } from './Link.svelte';
+export { default as Link, rewriteHref } from './Link.svelte';
 export { default as PhoneInput } from './PhoneInput.svelte';
 export { default as PinInput } from './PinInput.svelte';
 export { default as RadioGroup } from './RadioGroup.svelte';
@@ -47,7 +47,8 @@ export {
 	getValue,
 	targetMust,
 	capitalizeFirstLetter,
-	prefixZero
+	prefixZero,
+	trimEdges
 } from './util';
 export {
 	type ToolbarToggleState,

src/lib/util.ts

@@ -120,3 +120,26 @@ export const prefixZero = (str: string): string => {
 	}
 	return str;
 };
+
+/**
+ * Trims the specified character from the start and/or end of the string.
+ * @param str The string to trim.
+ * @param char The character to trim.
+ * @param trimStart Whether to trim from the start of the string. Default: true.
+ * @param trimEnd Whether to trim from the end of the string. Default: true.
+ * @returns The trimmed string.
+ */
+export const trimEdges = (str: string, char: string, trimStart?: boolean, trimEnd?: boolean) => {
+	let start = 0,
+		end = str.length;
+
+	if (trimStart || trimStart === undefined) {
+		while (start < end && str[start] === char) start++;
+	}
+
+	if (trimEnd || trimEnd === undefined) {
+		while (end > start && str[end - 1] === char) end--;
+	}
+
+	return str.substring(start, end);
+};

src/routes/+page.svelte

@@ -476,6 +476,23 @@
 	{/snippet}
 </div>
 
+<!-- Link with href rewriting -->
+<div class="component">
+	<p class="title">Link (with href rewriting)</p>
+
+	<p class="mb-3">
+		href rewriting allows you to prepend a basepath to relative links, making it easier to manage
+		URLs in your application. It is recommended to wrap this element with your own, e.g. AppLink,
+		that automatically provides the basepath from your app's configuration.
+	</p>
+
+	<div class="flex flex-col gap-3">
+		<Link href="/about" basepath="/sui-demo">Go to About Page (with basepath)</Link>
+		<Link href="https://svelte.dev" basepath="/sui-demo">External Svelte Site</Link>
+		<Link href="contact">Contact Us (relative link, no basepath)</Link>
+	</div>
+</div>
+
 <!-- Regular Dialog Demo -->
 <Dialog
 	bind:open={dialogOpen}