import { computed, readonly, ref } from "vue";
import { heartbeatSession } from "../api/authClient";
import { getToken } from "../utils/auth";

export type ConnectionStatus = "checking" | "online" | "degraded" | "offline";

const HEARTBEAT_INTERVAL_MS = 30_000;

const status = ref<ConnectionStatus>("checking");
const latencyMs = ref<number | null>(null);
const lastSuccessAt = ref<number | null>(null);
const lastCheckedAt = ref<number | null>(null);
let consumerCount = 0;
let heartbeatTimer: number | undefined;
let heartbeatPromise: Promise<void> | null = null;
let listenersRegistered = false;

const checkConnection = async () => {
  if (typeof navigator !== "undefined" && !navigator.onLine) {
    status.value = "offline";
    latencyMs.value = null;
    lastCheckedAt.value = Date.now();
    return;
  }
  if (heartbeatPromise) return heartbeatPromise;
  heartbeatPromise = (async () => {
    const startedAt = performance.now();
    try {
      const token = getToken();
      if (!token) {
        status.value = "offline";
        latencyMs.value = null;
        return;
      }
      await heartbeatSession(token);
      latencyMs.value = Math.max(1, Math.round(performance.now() - startedAt));
      lastSuccessAt.value = Date.now();
      status.value = "online";
    } catch (error: any) {
      latencyMs.value = null;
      status.value = error?.response ? "degraded" : "offline";
    } finally {
      lastCheckedAt.value = Date.now();
      heartbeatPromise = null;
    }
  })();
  return heartbeatPromise;
};

const handleOnline = () => {
  status.value = "checking";
  void checkConnection();
};

const handleOffline = () => {
  status.value = "offline";
  latencyMs.value = null;
  lastCheckedAt.value = Date.now();
};

const registerNetworkListeners = () => {
  if (listenersRegistered || typeof window === "undefined") return;
  listenersRegistered = true;
  window.addEventListener("online", handleOnline);
  window.addEventListener("offline", handleOffline);
};

const startConnectionMonitor = () => {
  consumerCount += 1;
  registerNetworkListeners();
  if (consumerCount === 1) {
    void checkConnection();
    heartbeatTimer = window.setInterval(() => void checkConnection(), HEARTBEAT_INTERVAL_MS);
  }
  return () => {
    consumerCount = Math.max(0, consumerCount - 1);
    if (consumerCount === 0 && heartbeatTimer) {
      window.clearInterval(heartbeatTimer);
      heartbeatTimer = undefined;
    }
  };
};

const statusLabel = computed(() => {
  if (status.value === "online") return "在线";
  if (status.value === "degraded") return "连接异常";
  if (status.value === "offline") return "已断开";
  return "检测中";
});

export const useConnectionStatus = () => ({
  status: readonly(status),
  statusLabel,
  latencyMs: readonly(latencyMs),
  lastSuccessAt: readonly(lastSuccessAt),
  lastCheckedAt: readonly(lastCheckedAt),
  checkConnection,
  startConnectionMonitor,
});