/**
 * Renders the notifications page, `/notifications`, for a signed-in user. It
 * reads them from `GET /api/notifications` and adds the ones `WSContext`
 * receives while it is open.
 *
 * @module
 */

import { useEffect, useMemo, useRef, useState } from "react";
import { Link } from "react-router";
import { t } from "@lingui/core/macro";
import { Trans } from "@lingui/react/macro";
import { relativeTime } from "../utils/shared/relativeTime.ts";

import { API_URL, NOTIFICATIONS_PAGE_SIZE } from "../config/api.ts";
import { useAuth } from "../hooks/auth/useAuth.ts";
import { useDocumentTitle } from "../hooks/shared/useDocumentTitle.ts";
import { ErrorCard } from "../components/shared/ErrorCard.tsx";
import { Tooltip } from "../components/shared/Tooltip.tsx";
import { LoadMoreButton } from "../components/shared/LoadMoreButton.tsx";
import { useWS } from "../hooks/ws/useWS.ts";
import type {
  CommentLikedData,
  DumpCommentedData,
  DumpUpvotedData,
  Notification,
  NotificationData,
  PlaylistDumpAddedData,
  PlaylistFollowedData,
  UserDumpPostedData,
  UserFollowedData,
  UserMentionedData,
} from "../../shared/notification.ts";
import { deserializeNotification } from "../utils/shared/deserialize.ts";
import { pageUrl, readPage } from "../utils/feed/pagedList.ts";
import { usePagedList } from "../hooks/feed/usePagedList.ts";
import { PageShell } from "../components/layout/PageShell.tsx";

type NotifIconKind =
  | "upvote"
  | "follow"
  | "dump"
  | "playlist"
  | "mention"
  | "comment"
  | "like";

function notifIconKind(type: Notification["type"]): NotifIconKind {
  switch (type) {
    case "dump_upvoted":
      return "upvote";
    case "playlist_followed":
      return "follow";
    case "user_followed":
      return "follow";
    case "user_dump_posted":
      return "dump";
    case "playlist_dump_added":
      return "playlist";
    case "user_mentioned":
      return "mention";
    case "dump_commented":
      return "comment";
    case "comment_liked":
      return "like";
  }
}

const UpvoteSvg = () => (
  <svg viewBox="0 0 10 10" width="11" height="11" fill="currentColor">
    <polygon points="5,1 9,9 1,9" />
  </svg>
);

const FollowSvg = () => (
  <svg viewBox="0 0 10 10" width="10" height="10" fill="currentColor">
    <polygon points="2,1 9,5 2,9" />
  </svg>
);

const HeartSvg = () => (
  <svg viewBox="0 0 10 10" width="10" height="10" fill="currentColor">
    <path d="M5 9 C2 6.5 0 5 0 2.8 C0 1.2 1.2 0 2.6 0 C3.6 0 4.5 0.6 5 1.5 C5.5 0.6 6.4 0 7.4 0 C8.8 0 10 1.2 10 2.8 C10 5 8 6.5 5 9 Z" />
  </svg>
);

function NotifIcon({ type }: { type: Notification["type"] }) {
  const kind = notifIconKind(type);
  const glyphs: Record<NotifIconKind, React.ReactNode> = {
    upvote: <UpvoteSvg />,
    follow: <FollowSvg />,
    dump: "🚚",
    playlist: "📜",
    mention: "@",
    comment: "💬",
    like: <HeartSvg />,
  };
  return (
    <span className={`notif-icon notif-icon--${kind}`}>
      {glyphs[kind]}
    </span>
  );
}

/**
 * Returns where notification `n` leads. A notification about a comment links
 * to its `#comment-<id>` anchor on the dump's page.
 */
function notificationLink(n: Notification): string {
  const data = n.data as NotificationData;
  switch (n.type) {
    case "user_followed":
      return `/users/${(data as UserFollowedData).followerUsername}`;
    case "playlist_followed":
      return `/playlists/${(data as PlaylistFollowedData).playlistId}`;
    case "user_dump_posted":
      return `/dumps/${(data as UserDumpPostedData).dumpId}`;
    case "playlist_dump_added":
      return `/dumps/${(data as PlaylistDumpAddedData).dumpId}`;
    case "dump_upvoted":
      return `/dumps/${(data as DumpUpvotedData).dumpId}`;
    case "dump_commented":
      return `/dumps/${(data as DumpCommentedData).dumpId}#comment-${
        (data as DumpCommentedData).commentId
      }`;
    case "comment_liked":
      return `/dumps/${(data as CommentLikedData).dumpId}#comment-${
        (data as CommentLikedData).commentId
      }`;
    case "user_mentioned": {
      const d = data as UserMentionedData;
      if (d.contextType === "comment") {
        return `/dumps/${d.dumpId}#comment-${d.contextId}`;
      }
      if (d.contextType === "dump") return `/dumps/${d.contextId}`;
      // A query string alone keeps this page, and `ChatProvider` opens the
      // chat over it.
      if (d.contextType === "chat") return `?chat=open`;
      return `/playlists/${d.contextId}`;
    }
  }
}

function notificationContent(n: Notification): React.ReactNode {
  const data = n.data as NotificationData;
  switch (n.type) {
    case "user_followed": {
      const d = data as UserFollowedData;
      return (
        <Trans>
          <strong>{d.followerUsername}</strong>
          {" started following you"}
        </Trans>
      );
    }
    case "playlist_followed": {
      const d = data as PlaylistFollowedData;
      return (
        <Trans>
          <strong>{d.followerUsername}</strong>
          {" followed your playlist "}
          <strong>{d.playlistTitle}</strong>
        </Trans>
      );
    }
    case "user_dump_posted": {
      const d = data as UserDumpPostedData;
      return (
        <Trans>
          <strong>{d.dumperUsername}</strong>
          {" posted "}
          <strong>{d.dumpTitle}</strong>
        </Trans>
      );
    }
    case "playlist_dump_added": {
      const d = data as PlaylistDumpAddedData;
      return (
        <Trans>
          <strong>{d.dumpTitle}</strong>
          {" was added to "}
          <strong>{d.playlistTitle}</strong>
        </Trans>
      );
    }
    case "dump_upvoted": {
      const d = data as DumpUpvotedData;
      return (
        <Trans>
          <strong>{d.voterUsername}</strong>
          {" upvoted "}
          <strong>{d.dumpTitle}</strong>
        </Trans>
      );
    }
    case "dump_commented": {
      const d = data as DumpCommentedData;
      return (
        <Trans>
          <strong>{d.commenterUsername}</strong>
          {" commented on "}
          <strong>{d.dumpTitle}</strong>
        </Trans>
      );
    }
    case "comment_liked": {
      const d = data as CommentLikedData;
      return (
        <Trans>
          <strong>{d.likerUsername}</strong>
          {" liked your comment on "}
          <strong>{d.dumpTitle}</strong>
        </Trans>
      );
    }
    case "user_mentioned": {
      const d = data as UserMentionedData;
      const where = d.contextTitle ||
        (d.contextType === "comment"
          ? t`a comment`
          : d.contextType === "chat"
          ? t`the chat`
          : t`a post`);
      return (
        <Trans>
          <strong>{d.mentionerUsername}</strong>
          {" mentioned you in "}
          <strong>{where}</strong>
        </Trans>
      );
    }
  }
}

/**
 * Returns how long ago `date` was when it was within a week, else its day and
 * month.
 */
function timeAgo(date: Date): string {
  const abs = Math.abs(Date.now() - date.getTime()) / 1000;
  if (abs < 7 * 86400) return relativeTime(date);
  return date.toLocaleDateString(undefined, { month: "short", day: "numeric" });
}

/** Returns the local midnight that starts the day of `d`, in epoch ms. */
function startOfDay(d: Date): number {
  return new Date(d.getFullYear(), d.getMonth(), d.getDate()).getTime();
}

/**
 * Returns `items` grouped under Today, Yesterday and Earlier, in that order,
 * without the empty groups. The labels are keys, which the page translates.
 */
function groupByDate(
  items: Notification[],
): { label: string; items: Notification[] }[] {
  const todayTs = startOfDay(new Date());
  const yesterdayTs = todayTs - 86_400_000;

  const buckets: Record<string, Notification[]> = {};
  for (const n of items) {
    const ts = startOfDay(n.createdAt);
    const key = ts >= todayTs
      ? "Today"
      : ts >= yesterdayTs
      ? "Yesterday"
      : "Earlier";
    (buckets[key] ??= []).push(n);
  }

  return (["Today", "Yesterday", "Earlier"] as const)
    .filter((k) => buckets[k]?.length)
    .map((label) => ({ label, items: buckets[label] }));
}

/**
 * Renders `/notifications`, for a signed-in user. Opening the page marks every
 * notification read on the server, and so does each that arrives while it is
 * open. The unread ones stay highlighted until the page is left.
 */
export function Notifications(): React.JSX.Element {
  useDocumentTitle(t`Notifications`);
  const { user, authFetch } = useAuth();
  const { clearUnreadNotifications, lastNotification } = useWS();
  const { state, loadMore } = usePagedList(
    user?.id,
    (page, signal) =>
      authFetch(
        pageUrl(`${API_URL}/api/notifications`, page, NOTIFICATIONS_PAGE_SIZE),
        { signal },
      ).then((res) => readPage(res, deserializeNotification)),
  );

  // Each new `lastNotification` is kept once, during render rather than in an
  // effect, so it shows in the same frame. The list may predate it or not.
  const [arrived, setArrived] = useState<Notification[]>([]);
  const [prevLastNotification, setPrevLastNotification] = useState(
    lastNotification,
  );
  if (prevLastNotification !== lastNotification && lastNotification !== null) {
    setPrevLastNotification(lastNotification);
    setArrived((a) => [lastNotification, ...a]);
  }
  const items = useMemo(() => {
    if (state.status !== "loaded") return [];
    const listed = new Set(state.data.items.map((n) => n.id));
    return [...arrived.filter((n) => !listed.has(n.id)), ...state.data.items];
  }, [state, arrived]);

  // Every notification is marked read on the server once the list shows, and
  // again for each that arrives while the page is open. Only the bell clears:
  // clearing the list too would take its dots and "new" count away a moment
  // after they appear. A failure leaves them unread for next time.
  const loaded = state.status === "loaded";
  const markedReadRef = useRef<Notification | null | undefined>(undefined);
  useEffect(() => {
    if (!loaded || markedReadRef.current === lastNotification) return;
    markedReadRef.current = lastNotification;
    authFetch(`${API_URL}/api/notifications/read-all`, { method: "POST" })
      .then((res) => {
        if (res.ok) clearUnreadNotifications();
      })
      .catch(() => {});
  }, [lastNotification, loaded, authFetch, clearUnreadNotifications]);

  const totalUnread = items.filter((n) => !n.read).length;

  return (
    <PageShell>
      <div className="notifications-page">
        <div className="notifications-header">
          <h1 className="notifications-title">
            <span className="notifications-title-bell">🔔</span>
            <Trans>Notifications</Trans>
          </h1>
          {state.status === "loaded" && totalUnread > 0 && (
            <span className="notifications-unread-pill">
              {totalUnread} <Trans>new</Trans>
            </span>
          )}
        </div>

        {state.status === "loading" && (
          <p className="page-loading">
            <Trans>Loading…</Trans>
          </p>
        )}
        {state.status === "error" && (
          <ErrorCard title={t`Failed to load`} message={state.error} />
        )}

        {state.status === "loaded" && items.length === 0 && (
          <div className="notifications-empty">
            <span className="notifications-empty-icon">🔕</span>
            <p>
              <Trans>Nothing here yet.</Trans>
            </p>
            <p className="notifications-empty-hint">
              <Trans>
                You'll be notified when someone follows your playlists, upvotes
                your dumps, or posts new content.
              </Trans>
            </p>
          </div>
        )}

        {state.status === "loaded" && items.length > 0 &&
          groupByDate(items).map(({ label, items }) => (
            <section key={label} className="notif-group">
              <h2 className="notif-group-label">
                {label === "Today"
                  ? t`Today`
                  : label === "Yesterday"
                  ? t`Yesterday`
                  : t`Earlier`}
              </h2>
              <ul className="notification-list">
                {items.map((n) => (
                  <li
                    key={n.id}
                    className={`notification-item${
                      !n.read ? " notification-item--unread" : ""
                    }`}
                  >
                    <Link
                      to={notificationLink(n)}
                      className="notification-item-link"
                    >
                      <NotifIcon type={n.type} />
                      <div className="notification-body">
                        <span className="notification-content">
                          {notificationContent(n)}
                        </span>
                        <Tooltip text={n.createdAt.toLocaleString()}>
                          <time
                            className="notification-time"
                            dateTime={n.createdAt.toISOString()}
                          >
                            {timeAgo(n.createdAt)}
                          </time>
                        </Tooltip>
                      </div>
                      {!n.read && (
                        <span className="notif-dot" aria-hidden="true" />
                      )}
                    </Link>
                  </li>
                ))}
              </ul>
            </section>
          ))}

        {state.status === "loaded" && state.data.hasMore && (
          <LoadMoreButton
            loadingMore={state.data.loadingMore}
            onClick={loadMore}
          />
        )}
      </div>
    </PageShell>
  );
}