/**
 * useNetworkStatus.ts — S57: Network Intelligence Layer (bandwidth estimation)
 *
 * Monitora connettività reale + latenza + bandwidth stimata.
 * Safari-safe: usa navigator.onLine + eventi window, nessun Worker.
 *
 * S57 rispetto a S55:
 *   + navigator.connection "change" events → react istantaneamente al cambio rete
 *   + downlink bandwidth estimation (navigator.connection.downlink, MB/s)
 *   + ping interval adattivo: 10s quando poor/slow, 30s quando good
 *   + campo bandwidthMbps esposto nell'API pubblica
 *   + classify usa downlink come segnale primario quando RTT non disponibile
 *
 * Stati qualità:
 *   offline   — navigator.onLine=false o ping fallisce ×2
 *   poor      — RTT >2500ms, downlink <0.5 Mbps, o effectiveType "2g"/"slow-2g"
 *   slow      — RTT 800-2500ms, downlink 0.5-1 Mbps, o effectiveType "3g"
 *   good      — RTT <800ms, downlink >2 Mbps (default se stima non disponibile)
 *
 * API:
 *   const { online, quality, rttMs, bandwidthMbps, since, justReconnected } = useNetworkStatus();
 */
import { useState, useEffect, useRef, useCallback } from "react";

export type NetworkQuality = "good" | "slow" | "poor" | "offline";

export interface NetworkState {
  online:          boolean;
  quality:         NetworkQuality;
  rttMs:           number | null;
  bandwidthMbps:   number | null;  // S57: downlink stimato in Mbps (null se non disponibile)
  since:           number;          // timestamp inizio stato attuale
  justReconnected: boolean;         // true per 4s dopo riconnessione
}

// ── Tipi Navigator Connection API (non standard, assente in @types/node) ──────
interface NetworkInformation extends EventTarget {
  effectiveType?: "slow-2g" | "2g" | "3g" | "4g";
  rtt?:           number;
  downlink?:      number;   // Mbps stimato
  saveData?:      boolean;
  onchange?:      ((ev: Event) => void) | null;
}
type NavigatorWithConn = Navigator & { connection?: NetworkInformation };

const PING_URL          = "https://agente-ai.pages.dev/favicon.ico";
const PING_TIMEOUT_MS   = 4000;
const PING_INTERVAL_GOOD_MS = 30_000;
const PING_INTERVAL_POOR_MS = 10_000;  // S57: più frequente quando rete è scarsa
const RECONNECT_SHOW_MS     = 4_000;

const DEFAULT: NetworkState = {
  online:        navigator.onLine,
  quality:       navigator.onLine ? "good" : "offline",
  rttMs:         null,
  bandwidthMbps: null,
  since:         Date.now(),
  justReconnected: false,
};

// ── Legge downlink da navigator.connection ─────────────────────────────────
function readDownlink(): number | null {
  const conn = (navigator as NavigatorWithConn).connection;
  if (!conn || conn.downlink === undefined) return null;
  return conn.downlink > 0 ? conn.downlink : null;
}

// ── Legge effectiveType da navigator.connection ────────────────────────────
function readEffectiveType(): NetworkQuality | null {
  const conn = (navigator as NavigatorWithConn).connection;
  if (!conn) return null;
  if (conn.effectiveType === "slow-2g" || conn.effectiveType === "2g") return "poor";
  if (conn.effectiveType === "3g") return "slow";
  return null;
}

// ── Classifica la qualità usando tutti i segnali disponibili ──────────────
function classify(
  rttMs: number | null,
  pingOk: boolean,
  downlinkMbps: number | null
): NetworkQuality {
  if (!pingOk) return "offline";

  // effectiveType ha precedenza quando disponibile (dato dal browser)
  const fromType = readEffectiveType();
  if (fromType) return fromType;

  // downlink come segnale primario S57
  if (downlinkMbps !== null) {
    if (downlinkMbps < 0.5) return "poor";
    if (downlinkMbps < 1.0) return "slow"; // Bug#2: was 2.0 — banner showed at 1.4 Mbps (sufficient for app)
    return "good";
  }

  // Fallback RTT
  if (rttMs === null) return "good";
  if (rttMs > 2500) return "poor";
  if (rttMs > 800)  return "slow";
  return "good";
}

async function measureRtt(): Promise<{ ok: boolean; rttMs: number | null }> {
  const t0 = performance.now();
  try {
    const ctrl  = new AbortController();
    const timer = setTimeout(() => ctrl.abort(), PING_TIMEOUT_MS);
    await fetch(`${PING_URL}?_=${Date.now()}`, {
      method: "HEAD",
      cache:  "no-store",
      signal: ctrl.signal,
    });
    clearTimeout(timer);
    return { ok: true, rttMs: Math.round(performance.now() - t0) };
  } catch {
    return { ok: false, rttMs: null };
  }
}

export function useNetworkStatus(): NetworkState {
  const [state, setState]       = useState<NetworkState>(DEFAULT);
  const reconnectTimer          = useRef<ReturnType<typeof setTimeout> | null>(null);
  const pingIntervalRef         = useRef<ReturnType<typeof setInterval> | null>(null);
  const pingCount               = useRef<number>(0);
  const currentQuality          = useRef<NetworkQuality>(DEFAULT.quality);

  // ── Ping + aggiornamento stato ───────────────────────────────────────────
  const runPing = useCallback(async () => {
    if (!navigator.onLine) {
      setState(s => s.online === false ? s : {
        online: false, quality: "offline",
        rttMs: null, bandwidthMbps: null,
        since: Date.now(), justReconnected: false,
      });
      currentQuality.current = "offline";
      return;
    }

    const [{ ok, rttMs }] = await Promise.all([measureRtt()]);
    const downlinkMbps    = readDownlink();

    if (!ok) {
      pingCount.current++;
      // Offline confermato solo dopo 2 ping falliti consecutivi (evita flap)
      if (pingCount.current >= 2) {
        setState(s => s.quality === "offline" ? s : {
          online: false, quality: "offline",
          rttMs: null, bandwidthMbps: null,
          since: Date.now(), justReconnected: false,
        });
        currentQuality.current = "offline";
      }
      return;
    }

    pingCount.current = 0;
    const quality     = classify(rttMs, true, downlinkMbps);

    setState(prev => {
      const wasOffline = !prev.online;
      const changed    = prev.quality !== quality || !prev.online;
      if (!changed && prev.bandwidthMbps === downlinkMbps) return prev;
      if (wasOffline && reconnectTimer.current) clearTimeout(reconnectTimer.current);
      currentQuality.current = quality;
      return {
        online:          true,
        quality,
        rttMs,
        bandwidthMbps:   downlinkMbps,
        since:           changed ? Date.now() : prev.since,
        justReconnected: wasOffline,
      };
    });

    // Auto-dismiss justReconnected dopo 4s
    if (reconnectTimer.current) clearTimeout(reconnectTimer.current);
    reconnectTimer.current = setTimeout(() => {
      setState(s => s.justReconnected ? { ...s, justReconnected: false } : s);
    }, RECONNECT_SHOW_MS);
  }, []);

  // ── Intervallo adattivo: rischedula quando qualità cambia ────────────────
  const rescheduleInterval = useCallback(() => {
    if (pingIntervalRef.current) clearInterval(pingIntervalRef.current);
    const ms = currentQuality.current === "good"
      ? PING_INTERVAL_GOOD_MS
      : PING_INTERVAL_POOR_MS;
    pingIntervalRef.current = setInterval(() => {
      runPing().then(rescheduleInterval).catch(() => {});
    }, ms);
  }, [runPing]);

  useEffect(() => {
    runPing().then(rescheduleInterval).catch(() => {});

    const onOnline = () => {
      pingCount.current = 0;
      runPing().then(rescheduleInterval).catch(() => {});
    };
    const onOffline = () => {
      currentQuality.current = "offline";
      setState({ online: false, quality: "offline", rttMs: null, bandwidthMbps: null, since: Date.now(), justReconnected: false });
    };

    window.addEventListener("online",  onOnline);
    window.addEventListener("offline", onOffline);

    // S57: navigator.connection "change" event — react istantaneamente
    const conn = (navigator as NavigatorWithConn).connection;
    const onConnChange = () => { runPing().then(rescheduleInterval).catch(() => {}); };
    conn?.addEventListener("change", onConnChange);

    return () => {
      if (pingIntervalRef.current) clearInterval(pingIntervalRef.current);
      window.removeEventListener("online",  onOnline);
      window.removeEventListener("offline", onOffline);
      conn?.removeEventListener("change", onConnChange);
      if (reconnectTimer.current) clearTimeout(reconnectTimer.current);
    };
  }, [runPing, rescheduleInterval]);

  return state;
}