"use client";

import { useCallback, useEffect, useRef, useState } from "react";

import { formatTimeDue, isReminderDue } from "@/lib/time-of-day";
import type { ScheduledBoardDTO } from "@/types/scheduled-todo";

// Separate from the panel's own collapsed-state key (scheduled-panel-provider.tsx).
const STORAGE_KEY = "organize:scheduled-notifications-enabled";

/**
 * Browser `Notification`s for scheduled to-dos, fired per each one's own
 * "Remind me" lead time (see lib/time-of-day.ts's REMIND_OPTIONS) -- which
 * may be before its time due, not necessarily at the same moment it's
 * promoted into Overdue (see ScheduledPanel; that's driven by timeDue
 * itself, unaffected by the reminder offset). This only reaches the user
 * while some copy of this tab is open somewhere (foreground or
 * backgrounded); there's no service worker `push` handler behind it, so
 * nothing fires once the tab itself is closed. That would need real Web
 * Push infrastructure (VAPID keys, a subscription table, a server-side
 * sender) -- a bigger step this intentionally doesn't take.
 */
export function useScheduledNotifications(board: ScheduledBoardDTO | null, now: Date) {
  // Whether the user has opted in *within the app* -- distinct from the
  // browser's own permission, which can only be granted or revoked through
  // its own UI, never by us. Same hydration-safe pattern as
  // ScheduledPanelProvider: default off on both server and first client
  // render, then read the persisted value (and the live permission) right
  // after mount.
  const [enabled, setEnabled] = useState(false);
  const [permission, setPermission] = useState<NotificationPermission | "unsupported">("unsupported");

  useEffect(() => {
    if (!("Notification" in window)) return;
    setPermission(Notification.permission);
    const stored = localStorage.getItem(STORAGE_KEY);
    // Only actually on if the browser still agrees -- a permission the user
    // revoked from browser settings since last time shouldn't look enabled.
    setEnabled(stored === "true" && Notification.permission === "granted");
  }, []);

  const requestEnable = useCallback(async () => {
    if (!("Notification" in window)) return false;
    let result = Notification.permission;
    if (result === "default") {
      result = await Notification.requestPermission();
      setPermission(result);
    }
    const granted = result === "granted";
    if (granted) {
      localStorage.setItem(STORAGE_KEY, "true");
      setEnabled(true);
    }
    return granted;
  }, []);

  const disable = useCallback(() => {
    localStorage.setItem(STORAGE_KEY, "false");
    setEnabled(false);
  }, []);

  // Occurrences already notified about this session, so the once-a-minute
  // tick in ScheduledPanel doesn't re-fire the same notification every time
  // it re-checks. Keyed the same way as everywhere else in this panel;
  // never pruned since occurrenceDate makes each key unique per calendar
  // day anyway, and the set only lives as long as the tab does.
  const notifiedRef = useRef<Set<string> | null>(null);

  useEffect(() => {
    if (!enabled || !board) return;

    const dueForReminder = board.today.occurrences.filter(
      (o) =>
        !o.completed &&
        o.timeDue &&
        o.remindMinutesBefore !== null &&
        isReminderDue(board.today.date, o.timeDue, o.remindMinutesBefore, now)
    );

    if (notifiedRef.current === null) {
      // First run after mounting (or reconnecting to a fresh board) --
      // baseline whatever's already due for a reminder instead of
      // notifying for old news the Overdue section (or an already-seen
      // reminder) is already showing.
      notifiedRef.current = new Set(dueForReminder.map((o) => `${o.scheduledTodoId}-${o.occurrenceDate}`));
      return;
    }

    for (const o of dueForReminder) {
      const key = `${o.scheduledTodoId}-${o.occurrenceDate}`;
      if (notifiedRef.current.has(key)) continue;
      notifiedRef.current.add(key);

      const notification = new Notification(o.title, {
        body: o.timeDue ? `Due at ${formatTimeDue(o.timeDue)}` : undefined,
        icon: "/icons/icon-192.png",
        tag: key, // replaces rather than stacking if this somehow runs twice
      });
      notification.onclick = () => {
        window.focus();
        notification.close();
      };
    }
  }, [enabled, board, now]);

  return {
    // "unsupported" hides the toggle entirely -- nothing to offer.
    supported: permission !== "unsupported",
    enabled,
    permission,
    requestEnable,
    disable,
  };
}