// ── The client half's library build ────────────────────────────────────────
//
// Produces `dist/entry.js`: one prebuilt ES module that core injects as a
// same-origin `<script type="module" src>` before `</body>`. The operator never
// builds anything (MODULE_SYSTEM.md §1.14), so this config is not a developer
// convenience — it is how the artifact that ships is made, and CI runs it.
//
// The normative contract is MODULE_API.md §3.6. Three mechanical details in here
// were each found the hard way and are worth reading before changing anything.
//
// **1. `resolve.alias` uses the ARRAY form with anchored regexes.** Vite's object
// form does PREFIX matching, so a `react` key also rewrites `react/jsx-runtime`
// — silently, to the wrong shim, and the chunk then fails at its first element
// with a message about `jsx` not being a function. `^react$` and
// `^react/jsx-runtime$` cannot collide.
//
// **2. The aliases replace `external`; they do not accompany it.** §3.6 shows
// both, and they do not compose: Rollup asks `external` BEFORE Vite's alias
// resolver runs, so a specifier listed there is marked external and never
// aliased. The chunk then ships bare `import 'react'` specifiers, which the
// browser cannot resolve without an import map — and core's `script-src 'self'`
// forbids the inline script an import map has to be. (`output.globals` would
// have covered iife/umd and does nothing for an ES module.) Slice 0 shipped with
// both, built cleanly, and emitted exactly that chunk; `scripts/checkExternals.js`
// is what caught it. So: alias only, and nothing in `external`.
//
// **3. What `external` was there to guard is guarded by `assertSharedNotBundled`
// below.** The risk it was covering is real — an alias that misses means a
// second React welded into the chunk, which loads fine and then throws about an
// invalid hook call somewhere unrelated. A resolution-time assertion catches
// that precisely, at build time, instead of by looking for fingerprints in
// minified output afterwards.

import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'
import { fileURLToPath } from 'node:url'

const shim = (name) => fileURLToPath(new URL(`./src/shim/${name}.js`, import.meta.url))

// The shared dependencies, in one place: what a module must never bundle, and
// the shim it is aliased to instead. Adding to this list means adding to
// `window.__rg` in core, which is a MODULE_API minor bump — not a decision this
// file can make on its own.
export const SHARED = [
  { specifier: 'react', shim: 'react' },
  { specifier: 'react/jsx-runtime', shim: 'jsx-runtime' },
  // A production `vite build` emits the non-dev runtime, but the plugin picks
  // per mode and a `--mode development` build would reach for this one. Aliased
  // rather than left to chance: the shim re-exports `jsxDEV` too.
  { specifier: 'react/jsx-dev-runtime', shim: 'jsx-runtime' },
  { specifier: 'react-dom', shim: 'react-dom' },
  { specifier: 'react-dom/client', shim: 'react-dom' },
  { specifier: 'react-router-dom', shim: 'react-router-dom' },
]

// The packages whose real source must never end up in the chunk.
//
// Stated independently of SHARED, and that is the whole point — an earlier
// version derived this from the alias list "so the two cannot disagree", which
// meant deleting an alias also deleted the guard against the thing that alias
// prevented. The guard then reported nothing on a chunk with react-router welded
// into it. What may not be bundled is a fact about core's `window.__rg`, not a
// function of what this config happens to alias; `test/build.test.js` asserts
// every SHARED specifier is covered here, which is the direction the dependency
// belongs in.
//
// `react-router` and `@remix-run/router` are react-router-dom's own internals.
// They cannot appear while the alias holds — nothing resolves through to them —
// so naming them costs nothing and closes the case where a module imports one
// directly and gets a second navigation context in a page that otherwise works.
export const SHARED_PACKAGES = ['react', 'react-dom', 'react-router-dom', 'react-router', '@remix-run/router']

/**
 * Fail the build if a shared dependency's real source is about to be bundled.
 *
 * This is the safety net, and it is a resolution-time one on purpose. The
 * alternative — grepping the built chunk for a fingerprint — has to guess at
 * strings that survive minification, and guesses at that are how a check ends up
 * passing on a chunk that carries a second React. Here there is nothing to
 * guess: if a module id resolved into `node_modules/react`, an alias missed, and
 * the alias that missed is named in the error.
 *
 * It hooks `transform` rather than `load`, and that is not interchangeable:
 * `load` is FIRST-WINS, so an earlier plugin returning the module's contents
 * means this hook is never called for it. Written against `load` this guard sat
 * in the build doing nothing, and a deliberately-broken alias produced a 24 kB
 * chunk with react-router welded into it and a green build — which is the exact
 * failure it exists to prevent. `transform` runs for every module, every time.
 */
function assertSharedNotBundled() {
  return {
    name: 'module-uo:assert-shared-not-bundled',
    enforce: 'post',
    transform(code, id) {
      const normalised = id.split('\\').join('/')
      const hit = SHARED_PACKAGES.find((pkg) => normalised.includes(`/node_modules/${pkg}/`))
      if (hit) {
        this.error(
          `"${hit}" resolved into node_modules (${normalised}). It must be aliased to a shim that ` +
          're-exports from window.__rg — there is exactly one React in the page and core owns it ' +
          '(MODULE_API.md §3.2, §3.6). Check resolve.alias in vite.config.js.',
        )
      }
      return null
    },
  }
}

export default defineConfig({
  plugins: [react(), assertSharedNotBundled()],
  resolve: {
    alias: SHARED.map(({ specifier, shim: name }) => ({
      find: new RegExp(`^${specifier.replace(/[/\\^$*+?.()|[\]{}]/g, '\\$&')}$`),
      replacement: shim(name),
    })),
  },
  build: {
    lib: {
      entry: fileURLToPath(new URL('./src/entry.jsx', import.meta.url)),
      formats: ['es'],
      // Unhashed, deliberately: `module.json` names this file, and a hashed name
      // would have to be discovered at runtime. Core answers the cache question
      // instead, serving it `no-cache` so a revalidation catches a new build
      // (MODULE_API.md §3.1).
      fileName: () => 'entry.js',
    },
    outDir: 'dist',
    emptyOutDir: true,
    // No inline bootstrap, for the same reason core disables it: an inline
    // script is refused under `script-src 'self'`, and the failure is a chunk
    // that never evaluates with a CSP report as the only clue.
    modulePreload: { polyfill: false },
    // `rollupOptions.external` is deliberately EMPTY — see note 2 at the top.
    rollupOptions: { external: [] },
  },
})