"use client";

import { useEffect, useRef } from "react";
import { useSession } from "@/lib/auth-client";
import { ReminderKind, loadHellthData } from "@/lib/hellth-data";

const labels: Record<ReminderKind, string> = {
  water: "Wasser",
  snack: "Snack",
  movement: "Bewegung",
};

function minutesOfDay(value: string) {
  const [hours = "0", minutes = "0"] = value.split(":");
  return Number(hours) * 60 + Number(minutes);
}

function canNotifyNow(startTime: string, endTime: string) {
  const now = new Date();
  const current = now.getHours() * 60 + now.getMinutes();
  return current >= minutesOfDay(startTime) && current <= minutesOfDay(endTime);
}

async function showReminder(kind: ReminderKind, message: string) {
  if (typeof window === "undefined" || !("Notification" in window)) return;
  if (Notification.permission !== "granted") return;

  const title = `Hellth Hub: ${labels[kind]}`;
  if ("serviceWorker" in navigator) {
    try {
      const registration = await navigator.serviceWorker.ready;
      await registration.showNotification(title, {
        body: message,
        tag: `hellth-${kind}`,
        badge: "/icon-192.png",
      });
      return;
    } catch {
      // Fall through to regular notification.
    }
  }

  new Notification(title, { body: message, tag: `hellth-${kind}` });
}

export function ReminderRunner() {
  const { data: session } = useSession();
  const userKey = session?.user?.id ?? session?.user?.email ?? null;
  const lastSentRef = useRef<Record<string, number>>({});

  useEffect(() => {
    if (!("serviceWorker" in navigator)) return;
    void navigator.serviceWorker.register("/hellth-sw.js").catch(() => undefined);
  }, []);

  useEffect(() => {
    if (!userKey) return;

    function tick() {
      const data = loadHellthData(userKey);
      const reminders = data.reminders;
      if (!reminders.enabled) return;
      if (typeof Notification === "undefined" || Notification.permission !== "granted") return;

      const now = Date.now();
      (Object.keys(reminders.rules) as ReminderKind[]).forEach((kind) => {
        const rule = reminders.rules[kind];
        if (!rule.enabled) return;
        if (!canNotifyNow(rule.startTime, rule.endTime)) return;

        const lastSentKey = `${userKey}:${kind}`;
        const lastSent = lastSentRef.current[lastSentKey] ?? 0;
        if (now - lastSent < rule.intervalMinutes * 60_000) return;

        lastSentRef.current[lastSentKey] = now;
        void showReminder(kind, rule.message);
      });
    }

    tick();
    const interval = window.setInterval(tick, 60_000);
    return () => window.clearInterval(interval);
  }, [userKey]);

  return null;
}