// React port of ../../daemonLink.ts. The link to the daemon behind this page:
// is it up, and which release is it? `RestartOverlay` (./RestartOverlay.tsx)
// renders what this reports. See docs/RESTART.md for the restart contract.

import { useEffect, useRef } from "react";
import { create } from "zustand";

import { getDaemonInfo } from "../../api.js";
import type { BuildInfo, DaemonInfo } from "../../types.js";

/**
 * - `connecting` — first probe hasn't landed yet.
 * - `online` — the daemon answered and is the same process, or a resolved new one.
 * - `reconnecting` — the socket dropped, but within the grace window; a blip
 *   shouldn't throw a modal in the user's face.
 * - `down` — unreachable past the grace window: the overlay blocks the UI and
 *   the poll runs until it answers.
 * - `updating` — it answered on a different commit; the page is reloading and
 *   stays blocked until it does.
 */
export type LinkState = "connecting" | "online" | "reconnecting" | "down" | "updating";

/** What happened between two `/api/info` replies. */
export type RestartKind = "same" | "restarted" | "upgraded";

/** How long a dropped socket may stay dropped before the UI blocks. Long enough
 *  to ride out a wifi hiccup, short enough that a real restart is visible. */
export const GRACE_MS = 1200;
/** Cadence of the `/api/info` poll while the daemon is unreachable. */
export const POLL_MS = 700;

/**
 * Compare two daemon replies.
 *
 * The commit decides first: a different one means new code, which for a browser
 * means new assets. The per-process `instance` catches the rest — a restart of
 * the same build, which needs no reload. A daemon built outside a git checkout
 * reports an empty commit, so an empty-vs-empty pair never counts as an
 * upgrade; the instance still reports the restart.
 */
export function compareIdentity(before: DaemonInfo, after: DaemonInfo): RestartKind {
  const a = before.build?.commit ?? "";
  const b = after.build?.commit ?? "";
  if (a && b && a !== b) return "upgraded";
  if (before.instance && after.instance && before.instance !== after.instance) return "restarted";
  return "same";
}

/** One line naming a release: `f89be4a716c7 · 2026-09-02`, with `(dirty)` when
 *  the build carried uncommitted changes. Empty builds say so rather than
 *  rendering a blank tooltip. */
export function formatRelease(build: BuildInfo | undefined): string {
  if (!build?.commit) return "unknown release";
  const day = build.commit_date ? build.commit_date.slice(0, 10) : "";
  const parts = [build.commit];
  if (day) parts.push(`· ${day}`);
  if (build.dirty) parts.push("(dirty)");
  return parts.join(" ");
}

/** Schedules a probe/grace timer; returns a handle `clearTimer` understands. */
export interface Scheduler {
  setTimer(fn: () => void, ms: number): number;
  clearTimer(handle: number): void;
}

const browserScheduler: Scheduler = {
  setTimer: (fn, ms) => window.setTimeout(fn, ms),
  clearTimer: (h) => window.clearTimeout(h),
};

export interface DaemonLinkState {
  state: LinkState;
  /** The release the daemon last reported. Undefined until the first probe,
   *  and on a daemon too old to carry one. */
  build?: BuildInfo;
  /** Hostname the daemon reports, for the indicator's tooltip. */
  hostname?: string;
  /** How many probes have failed in the current outage — the overlay counts
   *  attempts so a long restart doesn't look frozen. */
  attempts: number;
}

export interface DaemonLinkActions {
  /** One `/api/info` round-trip. Resolves `true` when the daemon answered. */
  probe(): Promise<boolean>;
  /** The events socket dropped. Starts the grace timer and the poll. */
  noteDisconnected(): void;
  /** The events socket came back. It carries no identity of its own, so the
   *  state only clears once a probe confirms *which* daemon answered — a
   *  reconnect to an upgraded daemon must reload, not resume. */
  noteConnected(): void;
  /** Stop polling. */
  stop(): void;
}

export type DaemonLinkStore = DaemonLinkState & DaemonLinkActions;

export interface DaemonLinkOptions {
  /** Injectable for tests; defaults to `GET /api/info`. */
  fetchInfo?: () => Promise<DaemonInfo>;
  scheduler?: Scheduler;
  /** What an upgrade does. Injectable so tests don't navigate. */
  reload?: () => void;
  graceMs?: number;
  pollMs?: number;
}

/** Builds an isolated daemon-link store — same shape as
 *  {@link ../../stores/catalogStore.js!createCatalogStore}: both a React hook
 *  and a plain object (`getState`/`subscribe`), so it drives the overlay
 *  whether or not React is the one calling `noteConnected`/`noteDisconnected`. */
export function createDaemonLinkStore(opts: DaemonLinkOptions = {}) {
  const fetchInfo = opts.fetchInfo ?? getDaemonInfo;
  const scheduler = opts.scheduler ?? browserScheduler;
  const reload = opts.reload ?? (() => window.location.reload());
  const graceMs = opts.graceMs ?? GRACE_MS;
  const pollMs = opts.pollMs ?? POLL_MS;

  let identity: DaemonInfo | null = null;
  let graceTimer: number | null = null;
  let pollTimer: number | null = null;

  return create<DaemonLinkStore>((set, get) => {
    function clearTimers(): void {
      if (graceTimer !== null) {
        scheduler.clearTimer(graceTimer);
        graceTimer = null;
      }
      if (pollTimer !== null) {
        scheduler.clearTimer(pollTimer);
        pollTimer = null;
      }
    }

    async function probe(): Promise<boolean> {
      let info: DaemonInfo;
      try {
        info = await fetchInfo();
      } catch {
        set((s) => ({ attempts: s.attempts + 1 }));
        return false;
      }
      const before = identity;
      identity = info;
      if (before && compareIdentity(before, info) === "upgraded") {
        // Stay blocked through the reload: an unlocked frame here would let the
        // user drive new server code from the bundle it just replaced.
        set({ state: "updating", build: info.build, hostname: info.hostname });
        reload();
        return true;
      }
      clearTimers();
      set({ state: "online", build: info.build, hostname: info.hostname, attempts: 0 });
      return true;
    }

    async function poll(): Promise<void> {
      const state = get().state;
      if (state === "online" || state === "updating") return;
      const ok = await probe();
      if (ok || pollTimer !== null) return;
      pollTimer = scheduler.setTimer(() => {
        pollTimer = null;
        void poll();
      }, pollMs);
    }

    return {
      state: "connecting",
      build: undefined,
      hostname: undefined,
      attempts: 0,

      probe,

      noteDisconnected() {
        const state = get().state;
        if (state === "down" || state === "updating") return;
        set({ state: "reconnecting", attempts: 0 });
        if (graceTimer === null) {
          graceTimer = scheduler.setTimer(() => {
            graceTimer = null;
            if (get().state === "reconnecting") set({ state: "down" });
            void poll();
          }, graceMs);
        }
      },

      noteConnected() {
        const state = get().state;
        if (state === "online" || state === "updating") return;
        void probe();
      },

      stop: clearTimers,
    };
  });
}

export type DaemonLinkStoreApi = ReturnType<typeof createDaemonLinkStore>;

export interface DaemonLinkProps {
  /** The link store this instance drives — `RestartOverlay` (and, later, the
   *  sidebar's status indicator) read the same one. */
  store: DaemonLinkStoreApi;
  /** The catalog store's `connected` field (docs/RESTART.md): the events
   *  socket dying is the earliest signal a restart happened, ahead of any
   *  poll. Pass `useStore(catalogStore, (s) => s.connected)`. */
  connected: boolean;
}

/**
 * Renders nothing — the controller that wires a `DaemonLinkStore` to the
 * catalog's socket state. Mount once near the app root; `RestartOverlay`
 * reads the store it drives.
 */
export function DaemonLink({ store, connected }: DaemonLinkProps): null {
  const mounted = useRef(false);

  useEffect(() => {
    if (!mounted.current) {
      mounted.current = true;
      void store.getState().probe();
      return;
    }
    if (connected) store.getState().noteConnected();
    else store.getState().noteDisconnected();
  }, [store, connected]);

  useEffect(() => () => store.getState().stop(), [store]);

  return null;
}