/**
 * Load acpx/runtime: prefer a global `npm install -g acpx`, then fall back to the
 * package-local `acpx` dependency (required for plain `pi` / ~/.pi package installs).
 */

import { createRequire } from "node:module";
import { existsSync } from "node:fs";
import { join } from "node:path";
import { pathToFileURL } from "node:url";
import { execFileSync } from "node:child_process";
import { homedir } from "node:os";

/** Minimal surface used by acpx-provider. */
export type AcpxRuntimeModule = {
  createAcpRuntime: (...args: any[]) => any;
  createFileSessionStore: (...args: any[]) => any;
  createAgentRegistry: (...args: any[]) => any;
};

let cachedRoots: string[] | null = null;
let cachedRuntime: Promise<AcpxRuntimeModule> | null = null;

function globalNodeModuleRoots(): string[] {
  if (cachedRoots) return cachedRoots;
  const roots: string[] = [];
  try {
    const root = execFileSync("npm", ["root", "-g"], {
      encoding: "utf-8",
      timeout: 15_000,
    }).trim();
    if (root) roots.push(root);
  } catch {
    /* ignore */
  }
  for (const candidate of [
    "/usr/local/lib/node_modules",
    join(homedir(), ".npm-global", "lib", "node_modules"),
  ]) {
    if (candidate && !roots.includes(candidate)) roots.push(candidate);
  }
  cachedRoots = roots;
  return roots;
}

async function importFromPackageRoot(pkgRoot: string): Promise<AcpxRuntimeModule | null> {
  const runtimeJs = join(pkgRoot, "dist", "runtime.js");
  if (existsSync(runtimeJs)) {
    return (await import(pathToFileURL(runtimeJs).href)) as AcpxRuntimeModule;
  }
  const pkgJson = join(pkgRoot, "package.json");
  if (!existsSync(pkgJson)) return null;
  try {
    const req = createRequire(pkgJson);
    const resolved = req.resolve("./dist/runtime.js");
    return (await import(pathToFileURL(resolved).href)) as AcpxRuntimeModule;
  } catch {
    return null;
  }
}

async function resolveAcpxRuntime(): Promise<AcpxRuntimeModule> {
  for (const root of globalNodeModuleRoots()) {
    const mod = await importFromPackageRoot(join(root, "acpx"));
    if (typeof mod?.createAcpRuntime === "function") return mod;
  }

  try {
    const mod = (await import("acpx/runtime")) as AcpxRuntimeModule;
    if (typeof mod?.createAcpRuntime === "function") return mod;
  } catch {
    /* ignore */
  }

  throw new Error(
    "acpx/runtime not found. Install with: npm install -g acpx " +
      "(or ensure the pi-config package dependency `acpx` is installed)",
  );
}

/**
 * Resolve acpx/runtime: global install first, then package dependency import.
 * Memoized — concurrent/repeated calls share one resolution. Rejected loads
 * clear the cache so a later install can succeed.
 */
export function loadAcpxRuntime(): Promise<AcpxRuntimeModule> {
  if (!cachedRuntime) {
    cachedRuntime = resolveAcpxRuntime().catch((err) => {
      cachedRuntime = null;
      throw err;
    });
  }
  return cachedRuntime;
}

/** Test helper — clear memoization between cases. */
export function clearAcpxRuntimeCache(): void {
  cachedRoots = null;
  cachedRuntime = null;
}