import { useEffect, useRef, useState } from "react";
import { useSyncExternalStore } from "react";
import { Bell, Trash2 } from "lucide-react";
import {
  clearAll,
  dismiss,
  getNotifications,
  getUnreadCount,
  markAllRead,
  subscribe,
} from "../lib/notifications";
import { LEVEL_STYLE } from "./Toaster";

function relTime(ts: number): string {
  const s = Math.round((Date.now() - ts) / 1000);
  if (s < 60) return "just now";
  const m = Math.round(s / 60);
  if (m < 60) return `${m}m ago`;
  const h = Math.round(m / 60);
  if (h < 24) return `${h}h ago`;
  const d = Math.round(h / 24);
  return `${d}d ago`;
}

export default function NotificationCenter() {
  const notifications = useSyncExternalStore(subscribe, getNotifications, getNotifications);
  const unread = useSyncExternalStore(subscribe, getUnreadCount, getUnreadCount);
  const [open, setOpen] = useState(false);
  const wrap = useRef<HTMLDivElement>(null);

  // Opening the center marks everything read.
  useEffect(() => {
    if (open) markAllRead();
  }, [open, notifications.length]);

  return (
    <div className="relative" ref={wrap}>
      <button
        onClick={() => setOpen((o) => !o)}
        title="Notifications"
        className="relative p-2 rounded-lg text-muted hover:text-fg hover:bg-card transition"
      >
        <Bell className="w-5 h-5" />
        {unread > 0 && (
          <span className="absolute -top-0.5 -right-0.5 min-w-[16px] h-4 px-1 rounded-full bg-accent text-accent-fg text-[10px] font-bold grid place-items-center">
            {unread > 9 ? "9+" : unread}
          </span>
        )}
      </button>

      {open && (
        <>
          <div className="fixed inset-0 z-20" onClick={() => setOpen(false)} />
          <div className="absolute right-0 mt-2 w-80 max-w-[calc(100vw-2rem)] rounded-xl border border-border bg-surface shadow-2xl z-30 flex flex-col max-h-[70vh]">
            <div className="flex items-center justify-between px-3 py-2 border-b border-border">
              <div className="text-sm font-semibold">Notifications</div>
              {notifications.length > 0 && (
                <button
                  onClick={clearAll}
                  className="flex items-center gap-1 text-xs text-muted hover:text-accent transition"
                  title="Clear all"
                >
                  <Trash2 className="w-3.5 h-3.5" />
                  Clear
                </button>
              )}
            </div>

            <div className="overflow-y-auto">
              {notifications.length === 0 ? (
                <div className="px-3 py-8 text-center text-sm text-muted">
                  No notifications yet.
                </div>
              ) : (
                notifications.map((n) => {
                  const { icon: Icon, color } = LEVEL_STYLE[n.level];
                  const needsAction = n.requiresInteraction && !n.dismissed;
                  return (
                    <div
                      key={n.id}
                      className={`flex items-start gap-2.5 px-3 py-2.5 border-b border-border/60 ${
                        needsAction ? "bg-accent/5" : ""
                      }`}
                    >
                      <Icon className={`w-4 h-4 shrink-0 mt-0.5 ${color}`} />
                      <div className="min-w-0 flex-1">
                        {n.title && <div className="text-sm font-semibold">{n.title}</div>}
                        <div className="text-sm break-words">{n.message}</div>
                        <div className="flex items-center gap-2 mt-0.5">
                          <span className="text-[11px] text-muted">{relTime(n.ts)}</span>
                          {needsAction && (
                            <span className="text-[10px] uppercase tracking-wide font-semibold text-accent">
                              Action needed
                            </span>
                          )}
                        </div>
                        {n.action && !n.dismissed && (
                          <button
                            onClick={() => {
                              n.action!.onClick();
                              dismiss(n.id);
                            }}
                            className="mt-1 text-accent text-sm font-semibold hover:underline"
                          >
                            {n.action.label}
                          </button>
                        )}
                      </div>
                    </div>
                  );
                })
              )}
            </div>
          </div>
        </>
      )}
    </div>
  );
}