Flight-Ops/lib/useGameState.ts

'use client';

import { useCallback, useEffect, useRef, useState } from 'react';
import type { StateSnapshot } from './game/state';

export interface GameStateResult {
  state: StateSnapshot | null;
  // True until the first successful fetch (stale-while-error afterwards).
  loading: boolean;
  error: string | null;
  // Trigger an immediate refetch (used after POST /api/sim so the UI updates without waiting for the next tick).
  refresh: () => void;
  // Push a snapshot straight into the shared state (v0.10.0): every action endpoint returns
  // the FULL post-action snapshot, so panes can render its result on click instead of waiting
  // for the next poll tick. The polling loop keeps running and simply overwrites it with the
  // server's truth on its next cycle (which also re-clears any transient pane error).
  applySnapshot: (snapshot: StateSnapshot) => void;
}

// Single fetch of the full game-state snapshot. Exported separately from the hook so it can be unit-tested with a mocked fetch.
export async function fetchState(): Promise<StateSnapshot> {
  const res = await fetch('/api/state', { cache: 'no-store' });
  if (!res.ok) throw new Error(`GET /api/state → HTTP ${res.status}`);
  const snapshot = (await res.json()) as StateSnapshot;
  // Dev/e2e hook (v0.15.0): the last successfully polled snapshot, so tests can compare what
  // the BROWSER received against a fresh node-side fetch. Client-only, harmless in prod.
  if (typeof window !== 'undefined') {
    (window as unknown as Record<string, unknown>).__flightLastSnapshot = {
      planeIds: snapshot.planes.map((p) => p.id),
      cash: snapshot.account.cash,
      clockMs: snapshot.simState.clockMs,
      at: Date.now(),
    };
  }
  return snapshot;
}

// The shell's single state source (v0.9.0): one snapshot feed for the whole page, so every pane
// renders from the same snapshot instead of running its own poll loops. ISS-129 (v0.57.0): primary
// transport is SSE — /api/events pushes a full snapshot after every sim tick; polling stays as an
// automatic fallback (no event within 5 s of connect, or on stream error) and stops again when fresh
// events flow. EventSource reconnects natively, so there is no custom reconnect logic here.
const SSE_URL = '/api/events';
const SSE_SILENCE_MS = 5_000;

export function useGameState(intervalMs = 1000): GameStateResult {
  const [state, setState] = useState<StateSnapshot | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);
  // Overlap guard: if the previous request is still in flight (slow server), skip this tick.
  const inFlightRef = useRef(false);

  const refresh = useCallback(() => {
    if (inFlightRef.current) return;
    inFlightRef.current = true;
    fetchState()
      .then((snapshot) => {
        setState(snapshot);
        setError(null);
        setLoading(false);
      })
      .catch((err: unknown) => {
        setError(err instanceof Error ? err.message : String(err));
      })
      .finally(() => {
        inFlightRef.current = false;
      });
  }, []);

  // v0.10.0 — instant action feedback: panes push the full snapshot returned by an
  // action endpoint into the shared state here (see GameStateResult.applySnapshot).
  const applySnapshot = useCallback((snapshot: StateSnapshot) => {
    setState(snapshot);
    setError(null);
    setLoading(false);
  }, []);

  useEffect(() => {
    let pollId: ReturnType<typeof setInterval> | null = null;
    let silenceTimer: ReturnType<typeof setTimeout> | null = null;
    let closed = false;

    const stopPolling = () => {
      if (pollId !== null) clearInterval(pollId);
      pollId = null;
    };
    // Fallback loop: immediate catch-up fetch, then the old interval.
    const startPolling = () => {
      if (closed || pollId !== null) return;
      refresh();
      pollId = setInterval(refresh, intervalMs);
    };

    let source: EventSource | null = null;
    try {
      source = new EventSource(SSE_URL);
    } catch {
      source = null; // no EventSource support — pure polling below
    }

    if (source !== null) {
      source.onmessage = (event) => {
        try {
          applySnapshot(JSON.parse(event.data));
        } catch {
          // malformed event — the next one overwrites it anyway
        }
        stopPolling(); // fresh push flow → polling no longer needed
        if (silenceTimer !== null) clearTimeout(silenceTimer);
        silenceTimer = setTimeout(startPolling, SSE_SILENCE_MS); // re-arm on EVERY message: a stream that goes silent after the first event (half-open connection — no onerror fires) must fall back to polling again, or state freezes until reload
      };
      source.onerror = () => startPolling(); // stream trouble → poll until pushes resume
      silenceTimer = setTimeout(startPolling, SSE_SILENCE_MS); // connected but silent for 5 s → poll
    } else {
      startPolling();
    }

    refresh(); // mount: same immediate fetch as before (fast first paint + __flightLastSnapshot)

    return () => {
      closed = true;
      source?.close();
      stopPolling();
      if (silenceTimer !== null) clearTimeout(silenceTimer);
    };
  }, [intervalMs, refresh, applySnapshot]);

  return { state, loading, error, refresh, applySnapshot };
}