platforms.js

import fs from 'node:fs';
import process from 'node:process';

/**
 * @typedef {{
 *   name: string;
 *   test: () => boolean;
 *   defaults: import('./index.js').AdapterOptions;
 *   done: (builder: import('@sveltejs/kit').Builder) => void;
 * }}
 * Platform */

// This function is duplicated in adapter-vercel
/** @param {import('@sveltejs/kit').Builder} builder */
function static_vercel_config(builder) {
	/** @type {any[]} */
	const prerendered_redirects = [];

	/** @type {Record<string, { path: string }>} */
	const overrides = {};

	for (let [src, redirect] of builder.prerendered.redirects) {
		if (src.replace(/\/$/, '') === redirect.location.replace(/\/$/, '')) {
			// ignore the extreme edge case of a `/foo` -> `/foo/` redirect,
			// which would only arise if the response was generated by a
			// `handle` hook or outside the app altogether (since you
			// can't declaratively create both routes)
		} else {
			// redirect both `/foo` and `/foo/` to `redirect.location`
			src = src.replace(/\/?$/, '/?');
		}

		prerendered_redirects.push({
			src,
			headers: {
				Location: redirect.location
			},
			status: redirect.status
		});
	}

	for (const [path, page] of builder.prerendered.pages) {
		let overrides_path = path.slice(1);

		if (path !== '/') {
			/** @type {string | undefined} */
			let counterpart_route = path + '/';

			if (path.endsWith('/')) {
				counterpart_route = path.slice(0, -1);
				overrides_path = path.slice(1, -1);
			}

			prerendered_redirects.push(
				{ src: path, dest: counterpart_route },
				{ src: counterpart_route, status: 308, headers: { Location: path } }
			);
		}

		overrides[page.file] = { path: overrides_path };
	}

	return {
		version: 3,
		routes: [
			...prerendered_redirects,
			{
				src: `/${builder.getAppPath()}/immutable/.+`,
				headers: {
					'cache-control': 'public, immutable, max-age=31536000'
				}
			},
			{
				handle: 'filesystem'
			},
			// Prevent incorrect caching: if a request to /_app/immutable/* doesn't match
			// a static file, return 404 instead of falling through to dynamic routes.
			// Otherwise, we could accidentally immutably cache dynamic content served
			// by the fallback function. `no-store` stops the earlier immutable header
			// from sticking to this 404, so a missing asset isn't cached for a year.
			{
				src: `/${builder.getAppPath()}/immutable/.+`,
				status: 404,
				headers: {
					'cache-control': 'no-store'
				},
				continue: false
			}
		],
		overrides
	};
}

/** @type {Platform[]} */
export const platforms = [
	{
		name: 'Vercel',
		test: () => !!process.env.VERCEL,
		defaults: {
			pages: '.vercel/output/static'
		},
		done: (builder) => {
			const config = static_vercel_config(builder);
			fs.writeFileSync('.vercel/output/config.json', JSON.stringify(config, null, '  '));
		}
	}
];