import {
  createBrowserLifecycleRuntime,
  type BrowserLifecycleRuntime,
} from "../adapters/platform/index.ts";
import type {
  ResolvedRuntimeCapabilities,
  RuntimeHealth,
  RuntimeStopReason,
} from "../contracts/runtime-capabilities.ts";
import type { ServiceWorkerRuntimeHost } from "../contracts/service-worker.ts";
import { createServiceWorkerRuntimeHost } from "./register-service-worker.ts";

/**
 * §3.4 / §20.3. Optional runtime host.
 *
 * Creating this object has no side effect: no listener, timer, network call,
 * IndexedDB open or worker is created until `startAfterMount()` runs from the
 * first committed React effect. `stop()` unwinds in reverse order.
 */

export type OptionalRuntimeHost = Readonly<{
  readonly realtime: null;
  readonly webWorkers: null;
  readonly serviceWorker: ServiceWorkerRuntimeHost | null;
  readonly offlineCommands: null;
  browserLifecycle(): BrowserLifecycleRuntime | null;
  health(): Readonly<Record<string, RuntimeHealth>>;
  startAfterMount(): Promise<void>;
  stop(reason?: RuntimeStopReason): Promise<void>;
}>;

export type OptionalRuntimeHostInput = Readonly<{
  capabilities: ResolvedRuntimeCapabilities;
  routerBasePath: string;
  buildId: string;
  /** Explicit host seam for deterministic lifecycle tests and platform shells. */
  serviceWorkerHost?: ServiceWorkerRuntimeHost | null;
  browserLifecycleHost?: Parameters<typeof createBrowserLifecycleRuntime>[0];
  host?: Parameters<typeof createServiceWorkerRuntimeHost>[0]["host"];
  blockers?: readonly (() => boolean)[];
  observe?: (observation: Readonly<{ event: string; outcome: string }>) => void;
}>;

export function createOptionalRuntimeHost(
  input: OptionalRuntimeHostInput,
): OptionalRuntimeHost {
  const { capabilities } = input;

  const serviceWorker = Object.hasOwn(input, "serviceWorkerHost")
    ? (input.serviceWorkerHost ?? null)
    : createServiceWorkerRuntimeHost({
        capabilities,
        routerBasePath: input.routerBasePath,
        buildId: input.buildId,
        ...(input.host ? { host: input.host } : {}),
        ...(input.blockers ? { blockers: input.blockers } : {}),
        ...(input.observe ? { observe: input.observe } : {}),
      });

  let lifecycle: BrowserLifecycleRuntime | null = null;
  let started = false;
  let startPromise: Promise<void> | null = null;
  let stopPromise: Promise<void> | null = null;
  let stopRequested = false;
  const health: Record<string, RuntimeHealth> = {
    realtime: capabilities.realtime.length === 0 ? "DISABLED" : "UNAVAILABLE",
    webWorkers: capabilities.webWorkers.length === 0 ? "DISABLED" : "UNAVAILABLE",
    serviceWorker: serviceWorker ? "UNAVAILABLE" : "DISABLED",
    offlineCommands: capabilities.offlineCommands ? "UNAVAILABLE" : "DISABLED",
  };

  /**
   * §3.4 start order:
   *   1. offline foreground browser lifecycle observer
   *   2. realtime runtime
   *   3. no Web Worker prewarm
   *   4. Service Worker active/cleanup controller
   */
  async function startAfterMount(): Promise<void> {
    // A stopped host is terminal. Its children (notably the Service Worker page
    // controller) own one-shot listeners and timers and cannot be resurrected.
    if (stopPromise) return stopPromise;
    if (startPromise) return startPromise;
    startPromise = (async () => {
      // 1. The lifecycle observer is the single window listener owner. It is
      // only created when something downstream can actually consume it.
      if (serviceWorker || capabilities.realtime.length > 0) {
        lifecycle = createBrowserLifecycleRuntime(input.browserLifecycleHost);
      }

      // 2. Realtime stays NOT_SELECTED until a product contribution exists
      // (§13.6), so there is nothing to start and nothing to observe.

      // 3. Web Workers are created lazily on first task; there is no prewarm.

      // 4. Service Worker registration or the exact-owned cleanup action.
      if (serviceWorker) {
        const outcome = await serviceWorker.start();
        // `stop()` may have fenced this generation while start was awaiting a
        // browser operation. A late result must never reactivate health.
        if (!stopRequested) {
          health.serviceWorker =
            outcome.kind === "ACTIVE"
              ? "AVAILABLE"
              : outcome.kind === "DISABLED"
                ? "DISABLED"
                : outcome.kind === "INCOMPATIBLE"
                  ? "INCOMPATIBLE"
                  : "DEGRADED";
        }
      }
      if (!stopRequested) started = true;
    })();
    return startPromise;
  }

  async function stop(
    reason: RuntimeStopReason = "APPLICATION_SHUTDOWN",
  ): Promise<void> {
    void reason;
    stopRequested = true;
    if (stopPromise) return stopPromise;
    stopPromise = (async () => {
      // Serialize teardown behind any in-flight browser registration. Cleanup
      // then observes the final acquired resources and unwinds them exactly once.
      await startPromise?.catch(() => {});
      // Reverse of the start order.
      if (serviceWorker && (started || startPromise)) {
        await serviceWorker.stop().catch(() => {});
      }
      if (serviceWorker) {
        health.serviceWorker = "DISABLED";
      }
      lifecycle?.dispose();
      lifecycle = null;
      started = false;
      startPromise = null;
    })();
    return stopPromise;
  }

  return Object.freeze({
    realtime: null,
    webWorkers: null,
    serviceWorker,
    offlineCommands: null,
    browserLifecycle: () => lifecycle,
    health: () => Object.freeze({ ...health }),
    startAfterMount,
    stop,
  });
}