"use client";

/**
 * /notifications — the signed-in user's notification feed.
 *
 * Lists everything newest-first and marks the whole feed read on open
 * (fire-and-forget), so the header bell's unread dot clears after a
 * visit. Each row links to the actor's profile, where follow requests can
 * be accepted/rejected.
 *
 * Anonymous visitors are bounced through the auth gate (then home if they
 * dismiss it), mirroring /u/me.
 */

import { useEffect, useState } from "react";
import { useRouter } from "next/navigation";
import Link from "next/link";
import { Bell } from "lucide-react";
import { useAuth } from "@/components/auth/auth-provider";
import { useAuthGate } from "@/components/auth/auth-gate";
import { useNotifications } from "@/components/notifications/notifications-provider";
import { notifications, type AppNotification } from "@/lib/social";
import { UserAvatar } from "@/components/ui/user-avatar";
import { timeAgo } from "@/lib/time";

export default function NotificationsPage() {
  const { user, loading } = useAuth();
  const { requireAuth } = useAuthGate();
  const { lastEventAt, clearUnread } = useNotifications();
  const router = useRouter();

  const [items, setItems] = useState<AppNotification[]>([]);
  const [state, setState] = useState<"loading" | "ready" | "error">("loading");

  // Auth gate — same pattern as /u/me.
  useEffect(() => {
    if (loading || user) return;
    let cancelled = false;
    (async () => {
      const ok = await requireAuth();
      if (!ok && !cancelled) router.replace("/");
    })();
    return () => {
      cancelled = true;
    };
  }, [loading, user, requireAuth, router]);

  // Load the feed + mark everything read once we have a user, and again
  // whenever a realtime notification arrives while the page is open
  // (lastEventAt bumps). Marking read here also clears the header badge.
  useEffect(() => {
    if (!user) return;
    let cancelled = false;
    notifications
      .list()
      .then((rows) => {
        if (!cancelled) {
          setItems(rows ?? []);
          setState("ready");
        }
      })
      .catch(() => {
        if (!cancelled) setState("error");
      });
    notifications
      .markAllRead()
      .then(() => clearUnread())
      .catch(() => {
        /* non-critical */
      });
    return () => {
      cancelled = true;
    };
  }, [user, lastEventAt, clearUnread]);

  if (loading || !user) {
    return (
      <main className="flex-1 flex items-center justify-center px-4 py-12">
        <p className="text-sm text-muted-foreground">
          {loading ? "Loading…" : "Sign in to view your notifications."}
        </p>
      </main>
    );
  }

  return (
    <main className="flex-1 max-w-2xl w-full mx-auto px-4 sm:px-6 py-6 space-y-6">
      <h1 className="font-[family-name:var(--font-title)] text-3xl font-semibold text-foreground">
        Notifications
      </h1>

      {state === "error" ? (
        <p className="text-sm text-destructive">
          Could not load notifications. Please try again.
        </p>
      ) : state === "loading" ? (
        <p className="text-sm text-muted-foreground">Loading…</p>
      ) : items.length === 0 ? (
        <Empty />
      ) : (
        <ul className="divide-y divide-border rounded-2xl border border-border overflow-hidden">
          {items.map((n) => (
            <NotificationRow key={n.id} n={n} selfHandle={user.handle} />
          ))}
        </ul>
      )}
    </main>
  );
}

function NotificationRow({
  n,
  selfHandle,
}: {
  n: AppNotification;
  selfHandle: string;
}) {
  // admin_message rows have no actor — they're a direct message from the team.
  const isAdmin = n.kind === "admin_message";
  const display = isAdmin
    ? "Prabhupāda Says"
    : n.actor_name || (n.actor_handle ? `@${n.actor_handle}` : "Someone");
  const message = messageFor(n);
  const unread = !n.read_at;

  const body = (
    <div
      className={cnRow(unread)}
    >
      <UserAvatar src={isAdmin ? null : n.actor_avatar_url} name={display} />
      <div className="min-w-0 flex-1">
        {isAdmin ? (
          <p className="text-sm text-foreground leading-snug whitespace-pre-line">
            <span className="font-semibold">{display}</span>
            {n.body ? <span className="block mt-0.5">{n.body}</span> : null}
          </p>
        ) : (
          <p className="text-sm text-foreground leading-snug">
            <span className="font-semibold">{display}</span> {message}
          </p>
        )}
        <p className="text-xs text-muted-foreground mt-0.5">
          {timeAgo(n.created_at)}
        </p>
      </div>
      {unread ? (
        <span className="mt-1.5 size-2 shrink-0 rounded-full bg-primary" />
      ) : null}
    </div>
  );

  // A like links to your own post; a mention links to the actor's post you
  // were tagged in; everything else links to the actor's profile.
  const href =
    n.kind === "post_like" && n.post_id
      ? `/u/${selfHandle}/posts#post-${n.post_id}`
      : n.kind === "post_mention" && n.post_id && n.actor_handle
        ? `/u/${n.actor_handle}/posts#post-${n.post_id}`
        : (n.kind === "post_comment" ||
              n.kind === "comment_reply" ||
              n.kind === "comment_mention") &&
            n.post_id &&
            n.post_author_handle
          ? `/u/${n.post_author_handle}/posts#post-${n.post_id}`
          : n.actor_handle
            ? `/u/${n.actor_handle}`
            : null;

  return href ? (
    <li>
      <Link href={href} className="block">
        {body}
      </Link>
    </li>
  ) : (
    <li>{body}</li>
  );
}

function cnRow(unread: boolean) {
  return [
    "flex items-start gap-3 px-4 py-3 transition-colors hover:bg-muted/50",
    unread ? "bg-primary/5" : "",
  ].join(" ");
}

/** Human-readable tail for each notification kind. Add cases as new
 *  notification kinds are introduced on the backend. */
function messageFor(n: AppNotification): string {
  switch (n.kind) {
    case "follow_request":
      return "requested to follow you.";
    case "follow_accepted":
      return "accepted your follow request.";
    case "post_like": {
      const others = (n.actor_count ?? 1) - 1;
      if (others <= 0) return "liked your post.";
      return `and ${others} ${others === 1 ? "other" : "others"} liked your post.`;
    }
    case "post_mention":
      return "mentioned you in a post.";
    case "post_comment":
      return "commented on your post.";
    case "comment_reply":
      return "replied to your comment.";
    case "comment_mention":
      return "mentioned you in a comment.";
    case "admin_message":
      return n.body ?? "sent you a message.";
    default:
      return "sent you a notification.";
  }
}

function Empty() {
  return (
    <div className="flex flex-col items-center text-center gap-3 py-16 text-muted-foreground">
      <Bell className="size-8" />
      <p className="text-sm">No notifications yet.</p>
    </div>
  );
}