#!/usr/bin/env bun
/**
 * link-polyfill.ts — Reactive local overlay of a data-layer PROVIDER's checkout into
 * node_modules. One script, one provider per run; only the paths differ between them.
 *
 * PROVIDERS (first non-flag argument; defaults to `polyfill`):
 *   polyfill  → node_modules/@ng-eventually/polyfill   override: NG_EVENTUALLY_LOCAL
 *   indexing  → node_modules/@ng-helpers/indexing      override: NG_HELPERS_LOCAL
 *
 * WHY a copy-overlay and not a symlink (identical for every provider):
 *   A committed prod dependency installs from Gitea (git+https) into pnpm's store WITHOUT
 *   its own node_modules/@ng-org, so @ng-org/web resolves UP to Festipod → ONE @ng-org
 *   instance (one verifier). A local CHECKOUT, however, carries its own node_modules/*
 *   (links into that provider's own dev tree). Symlinking node_modules/<pkg> to the
 *   checkout would put the checkout's copies in the resolution path → a SECOND @ng-org
 *   (and, for `indexing`, a second @ng-eventually/polyfill) → broken SDK, two verifiers.
 *   So we overlay a real directory containing ONLY the provider's source (no node_modules):
 *   shared packages still resolve up to Festipod, single instance preserved.
 *
 * WHAT IT DOES:
 *   1. Replaces node_modules/<package> (the pnpm store symlink) with a real directory
 *      holding the local checkout's package.json + src (NO node_modules).
 *   2. Asserts the single-instance invariant — every package this provider SHARES with
 *      Festipod must resolve to the same realpath from Festipod and from the overlay —
 *      and aborts if it would break.
 *   3. Watches the local checkout's src and copies each change into the overlay.
 *
 * ⚠️ RESTART `bun run dev` AFTER THIS SCRIPT WRITES — a rebuild is NOT a substitute.
 * A running dev server NEVER picks up a package refreshed inside node_modules, not even
 * across a genuine rebuild: VERIFIED in a controlled test, an application-source edit
 * produced a new bundle hash and the rebuilt bundle STILL carried the stale dependency.
 * The server's resolution of that import is pinned at process start and a rebuild does not
 * re-resolve it. Only restarting serves the fresh copy, and nothing warns you — a stale
 * server looks exactly like a current one. See
 * .project/concepts/tech-stack/caveat_polyfill-overlay-needs-a-dev-restart.md, which cost
 * an hour to learn. Watching copies the files; it does not make anything reload them.
 *
 * USAGE (reactive dev):
 *   Terminal 1:  pnpm run link:polyfill       # or: pnpm run link:indexing
 *   Terminal 2:  bun run dev                  # portless festipod bun --hot src/index.ts
 *   Edit the checkout's src → it lands in node_modules → RESTART dev to pick it up.
 *
 *   pnpm run link:indexing --once             # overlay + verify, no watch (CI / one-shot)
 *   Return to the committed git-installed dependencies:  pnpm install
 */
import { existsSync, lstatSync, mkdirSync, rmSync, cpSync, copyFileSync, realpathSync } from "node:fs";
import { watch } from "node:fs";
import { join, dirname } from "node:path";

interface Provider {
  /** Package as installed, e.g. "@ng-eventually/polyfill" — also its node_modules path. */
  readonly packageName: string;
  /** Local checkout used when the env override is unset. */
  readonly defaultLocal: string;
  /** Env var overriding the local checkout path. */
  readonly envOverride: string;
  /**
   * Packages this provider SHARES with Festipod and that must stay single-instance.
   * Each is resolved from Festipod and from the overlay; the realpaths must match.
   */
  readonly singletons: readonly string[];
}

const PROVIDERS: Record<string, Provider> = {
  polyfill: {
    packageName: "@ng-eventually/polyfill",
    defaultLocal: "/home/sylvain/projects/nextgraph/ng-eventually-js/packages/polyfill",
    envOverride: "NG_EVENTUALLY_LOCAL",
    singletons: ["@ng-org/web"],
  },
  indexing: {
    packageName: "@ng-helpers/indexing",
    defaultLocal: "/home/sylvain/projects/nextgraph/ng-helpers",
    envOverride: "NG_HELPERS_LOCAL",
    // Consumes the polyfill, so BOTH it and the verifier underneath must stay single.
    singletons: ["@ng-eventually/polyfill", "@ng-org/web"],
  },
};

const FESTIPOD = realpathSync(join(import.meta.dir, ".."));
const args = process.argv.slice(2);
const ONCE = args.includes("--once");
const KEY = args.find((a) => !a.startsWith("-")) ?? "polyfill";

function fail(msg: string): never {
  console.error(`✖ link:${KEY} — ${msg}`);
  process.exit(1);
}

const provider = PROVIDERS[KEY];
if (!provider) {
  fail(`unknown provider "${KEY}" — expected one of: ${Object.keys(PROVIDERS).join(", ")}`);
}

const LOCAL = process.env[provider.envOverride] ?? provider.defaultLocal;
const TARGET = join(FESTIPOD, "node_modules", ...provider.packageName.split("/"));
const SRC_LOCAL = join(LOCAL, "src");
const SRC_TARGET = join(TARGET, "src");

if (!existsSync(join(LOCAL, "package.json"))) {
  fail(`local checkout not found at ${LOCAL} (set ${provider.envOverride} to override)`);
}
if (!existsSync(SRC_LOCAL)) {
  fail(`local checkout has no src/ at ${SRC_LOCAL}`);
}

// 1. Replace the pnpm store symlink with a real overlay dir (metadata + src, NO node_modules).
console.log(`→ overlaying local ${provider.packageName}: ${LOCAL}`);
if (existsSync(TARGET) || lstatSync(TARGET, { throwIfNoEntry: false })) {
  rmSync(TARGET, { recursive: true, force: true });
}
mkdirSync(TARGET, { recursive: true });
for (const meta of ["package.json", "tsconfig.json", "README.md"]) {
  const from = join(LOCAL, meta);
  if (existsSync(from)) copyFileSync(from, join(TARGET, meta));
}
// Copy src fresh (NEVER a node_modules dir — that is what guarantees single instances).
cpSync(SRC_LOCAL, SRC_TARGET, { recursive: true });

// 2. Assert the single-instance invariant for every package shared with Festipod.
const overlayReal = realpathSync(TARGET);
for (const spec of provider.singletons) {
  const fromFestipod = realpathSync(Bun.resolveSync(spec, FESTIPOD));
  const fromOverlay = realpathSync(Bun.resolveSync(spec, overlayReal));
  console.log(`  ${spec} (Festipod): ${fromFestipod}`);
  console.log(`  ${spec} (overlay) : ${fromOverlay}`);
  if (fromFestipod !== fromOverlay) {
    fail(
      `single-instance invariant BROKEN — ${spec} resolves to two different realpaths.\n` +
        "  The overlay must not contain its own node_modules. Aborting.",
    );
  }
}
console.log(`✓ single instance preserved for: ${provider.singletons.join(", ")}`);

if (ONCE) {
  console.log("✓ overlay ready (--once, not watching)");
  process.exit(0);
}

// 3. Watch and copy on change. This keeps the overlay CURRENT; it does NOT make a running
// dev server notice — not even across a rebuild (see the header). Restart it.
console.log(`👀 watching ${SRC_LOCAL} → ${SRC_TARGET} (Ctrl-C to stop)`);
watch(SRC_LOCAL, { recursive: true }, (_event, filename) => {
  if (!filename) return;
  const from = join(SRC_LOCAL, filename);
  const to = join(SRC_TARGET, filename);
  try {
    if (existsSync(from)) {
      mkdirSync(dirname(to), { recursive: true });
      copyFileSync(from, to);
      console.log(`  ↻ ${filename}`);
    } else if (existsSync(to)) {
      rmSync(to, { force: true });
      console.log(`  ✗ ${filename} (removed)`);
    }
  } catch (err) {
    console.error(`  ! failed to sync ${filename}:`, err);
  }
});