From fb2185083c2b6736430d0910bf57977e3e4a9c13 Mon Sep 17 00:00:00 2001
From: Ax333l <main@axelen.xyz>
Date: Fri, 4 Nov 2022 19:20:33 +0100
Subject: [PATCH] feat: add vercel routes config generator

This is so we do not need to force trailing slashes.
---
 src/_vercel-moment.js | 82 +++++++++++++++++++++++++++++++++++++++++++
 svelte.config.js      |  8 ++---
 2 files changed, 86 insertions(+), 4 deletions(-)
 create mode 100644 src/_vercel-moment.js

diff --git a/src/_vercel-moment.js b/src/_vercel-moment.js
new file mode 100644
index 0000000..01e681c
--- /dev/null
+++ b/src/_vercel-moment.js
@@ -0,0 +1,82 @@
+import fs from 'fs';
+
+// This code was stolen from https://github.com/sveltejs/kit/blob/master/packages/adapter-static/platforms.js
+
+// sveltekit does things like this instead of actually just using ts for some reason.
+/** @param {import('@sveltejs/kit').Builder} builder */
+function vercel_routes(builder) {
+	/** @type {any[]} */
+	const routes = [
+		{
+			src: `/${builder.config.kit.appDir}/immutable/.+`,
+			headers: {
+				'cache-control': 'public, immutable, max-age=31536000'
+			}
+		}
+	];
+
+	// explicit redirects
+	for (const [src, redirect] of builder.prerendered.redirects) {
+		routes.push({
+			src,
+			headers: {
+				Location: redirect.location
+			},
+			status: redirect.status
+		});
+	}
+
+	// prerendered pages
+	for (const [src, page] of builder.prerendered.pages) {
+		routes.push({
+			src,
+			dest: `${builder.config.kit.appDir}/prerendered/${page.file}`
+		});
+	}
+
+	// implicit redirects (trailing slashes)
+	for (const [src] of builder.prerendered.pages) {
+		if (src !== '/') {
+			routes.push({
+				src: src.endsWith('/') ? src.slice(0, -1) : src + '/',
+				headers: {
+					location: src
+				},
+				status: 308
+			});
+		}
+	}
+
+	routes.push({
+		handle: 'filesystem'
+	});
+
+	return routes;
+}
+
+export function wrap(adapter, opts) {
+	if (!process.env.VERCEL) {
+		// we don't have to bother :)
+		return adapter(opts);
+	}
+
+	// Not exactly what adapter-static does, but it works.
+	opts.pages = '.vercel/output/static';
+
+	adapter = adapter(opts);
+
+	const adapt_fn = adapter.adapt;
+	adapter.adapt = async (builder) => {
+		const result = await adapt_fn(builder);
+		fs.writeFileSync(
+			'.vercel/output/config.json',
+			JSON.stringify({
+				version: 3,
+				routes: vercel_routes(builder)
+			})
+		);
+		return result;
+	}
+
+	return adapter;
+}
diff --git a/svelte.config.js b/svelte.config.js
index 55305a6..b5327fd 100644
--- a/svelte.config.js
+++ b/svelte.config.js
@@ -1,6 +1,8 @@
 import adapter from '@sveltejs/adapter-static';
 import preprocess from 'svelte-preprocess';
 
+import { wrap } from './src/_vercel-moment.js';
+
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
 	// Consult https://github.com/sveltejs/svelte-preprocess
@@ -9,13 +11,11 @@ const config = {
 
 	kit: {
 		// adapter-static has vercel detection, but that does not let you set a custom 404 page easily.
-		// Instead, we have to disable it and set trailing slash to always.
-		adapter: adapter({
+		// Instead, we have to use a wrapper that generates a vercel config if on vercel...
+		adapter: wrap(adapter, {
 			pages: "public",
 			fallback: "404.html"
 		}),
-
-		trailingSlash: 'always'
 	}
 };