import { computed, onMounted, onUnmounted, readonly, shallowRef } from "vue";

import type { DesktopRuntimeSnapshot } from "../types";

const RUNTIME_POLL_INTERVAL_MS = 15_000;

const snapshot = shallowRef<DesktopRuntimeSnapshot | null>(null);
const loading = shallowRef(false);
const error = shallowRef<string | null>(null);

let intervalHandle: ReturnType<typeof setInterval> | null = null;
let subscribers = 0;
let visibilityListenerBound = false;
let runtimeInvalidationUnsubscribe: (() => void) | null = null;

function isPageVisible(): boolean {
  return typeof document === "undefined" || document.visibilityState === "visible";
}

async function refreshRuntimeSnapshot() {
  loading.value = true;
  error.value = null;

  try {
    if (!window.desktopBridge?.app?.runtimeSnapshot) {
      snapshot.value = null;
      error.value = "desktop runtime bridge unavailable";
      return;
    }

    snapshot.value = await window.desktopBridge.app.runtimeSnapshot();
  } catch (err) {
    error.value = err instanceof Error ? err.message : "runtime snapshot unavailable";
  } finally {
    loading.value = false;
  }
}

async function refreshAccounts() {
  if (!window.desktopBridge?.app?.refreshRuntimeAccounts) {
    await refreshRuntimeSnapshot();
    return;
  }

  loading.value = true;
  error.value = null;

  try {
    await window.desktopBridge.app.refreshRuntimeAccounts();
    snapshot.value = await window.desktopBridge.app.runtimeSnapshot();
  } catch (err) {
    error.value = err instanceof Error ? err.message : "refresh accounts failed";
  } finally {
    loading.value = false;
  }
}

function stopPolling() {
  if (!intervalHandle) {
    return;
  }

  clearInterval(intervalHandle);
  intervalHandle = null;
}

function syncPollingState() {
  if (subscribers === 0 || !isPageVisible()) {
    stopPolling();
    return;
  }

  if (intervalHandle) {
    return;
  }

  intervalHandle = setInterval(() => {
    void refreshRuntimeSnapshot();
  }, RUNTIME_POLL_INTERVAL_MS);
}

function handleVisibilityChange() {
  if (isPageVisible()) {
    void refreshRuntimeSnapshot();
  }

  syncPollingState();
}

function bindVisibilityListener() {
  if (visibilityListenerBound || typeof document === "undefined") {
    return;
  }

  document.addEventListener("visibilitychange", handleVisibilityChange);
  visibilityListenerBound = true;
}

function bindRuntimeInvalidationListener() {
  if (runtimeInvalidationUnsubscribe || !window.desktopBridge?.app?.onRuntimeInvalidated) {
    return;
  }

  runtimeInvalidationUnsubscribe = window.desktopBridge.app.onRuntimeInvalidated(() => {
    if (isPageVisible()) {
      void refreshRuntimeSnapshot();
    }
  });
}

function unbindVisibilityListener() {
  if (!visibilityListenerBound || typeof document === "undefined") {
    return;
  }

  document.removeEventListener("visibilitychange", handleVisibilityChange);
  visibilityListenerBound = false;
}

function unbindRuntimeInvalidationListener() {
  runtimeInvalidationUnsubscribe?.();
  runtimeInvalidationUnsubscribe = null;
}

export function useDesktopRuntime() {
  onMounted(() => {
    subscribers += 1;
    bindVisibilityListener();
    bindRuntimeInvalidationListener();
    if (!snapshot.value && !loading.value) {
      void refreshRuntimeSnapshot();
    }
    syncPollingState();
  });

  onUnmounted(() => {
    subscribers = Math.max(0, subscribers - 1);
    if (subscribers === 0) {
      stopPolling();
      unbindVisibilityListener();
      unbindRuntimeInvalidationListener();
      return;
    }

    syncPollingState();
  });

  return {
    snapshot: readonly(snapshot),
    loading: readonly(loading),
    error: readonly(error),
    refresh: refreshRuntimeSnapshot,
    refreshAccounts,
    hasSnapshot: computed(() => snapshot.value !== null),
  };
}