/**
 * Live updates from the server reach the pages through the three contexts
 * declared here: votes and likes, dumps, playlists, comments, profiles and
 * notifications in one, the chat in another, who is online in the third. They
 * are split so that a feed doesn't re-render with every chat message or
 * presence change. `WSProvider` fills them from its WebSocket, and components
 * read them with `useWS`, `useWSChat` and `useWSPresence`.
 *
 * @module
 */

import { createContext } from "react";
import type { ChatMessage } from "../../../shared/chat.ts";
import type { Comment } from "../../../shared/comment.ts";
import type { Dump } from "../../../shared/dump.ts";
import type { Notification } from "../../../shared/notification.ts";
import type { OnlineUser } from "../../../shared/ws.ts";
import type { Playlist } from "../../../shared/playlist.ts";
import type { PublicUser } from "../../../shared/user.ts";

/**
 * Keeps a user's upvoted list live, on their profile's overview and tab.
 * `WSProvider` sets it as `lastVoteEvent` on each `votes_update`, and
 * `useUpvotedList` adds or drops the dump.
 */
export interface VoteEvent {
  dumpId: string;
  voterId: string;
  action: "cast" | "remove";
}

/**
 * Keeps the playlists on screen up to date, in lists, on a playlist's page and
 * on a dump's page. `WSProvider` sets it as `lastPlaylistEvent` on each
 * `playlist_*` message; lists apply it through `usePlaylistListSync`, a
 * playlist's page through `usePlaylist`. Which fields are set depends on
 * `type`.
 */
export interface PlaylistEvent {
  type: "created" | "updated" | "deleted" | "dumps_updated";
  playlistId: string;
  /** Set when created or updated. */
  playlist?: Playlist;
  /** The owner's id, set when deleted. */
  userId?: string;
  /**
   * Set when the dumps changed. It lists only the dumps this user may see, in
   * order.
   */
  dumpIds?: string[];
  /** Set when the dumps changed. It counts private dumps too. */
  dumpCount?: number;
}

/**
 * Keeps comment threads and comment counts live. `WSProvider` sets it as
 * `lastCommentEvent` on each `comment_*` message; the `Dump` page applies it
 * to its thread, and `useDumpListSync` to the counts on dump cards.
 */
export interface CommentEvent {
  type: "created" | "deleted" | "updated";
  dumpId: string;
  /** Set when created or updated. */
  comment?: Comment;
  /** Set when deleted. */
  commentId?: string;
}

/**
 * Keeps a profile page live while its user edits their profile. `WSProvider`
 * sets it as `lastUserEvent` on each `user_updated`, which the server sends on
 * any change to a profile, and `useProfile` applies it.
 */
export interface UserEvent {
  user: PublicUser;
}

/**
 * Quotes the message a chat message replies to. `ChatModal` shows it in the
 * reply bar once the user picks it, and it stays on the pending message so
 * the quote shows before the server's echo. Only `id` goes to the server.
 */
export interface ChatReplyTarget {
  id: string;
  author: string;
  body: string;
}

/**
 * Shows a chat message the moment the user sends it, and lets them retry it if
 * it fails. `WSProvider` holds it until the server echoes the message back, and
 * `ChatModal` shows it, as `PendingItem`, after the messages the server has.
 */
export interface PendingChatMessage {
  /**
   * Sent with `chat_send` and returned with the echo or the error. A retry
   * gets a new one, so a late echo of the first attempt can't retire it.
   */
  nonce: string;
  body: string;
  replyTo?: ChatReplyTarget;
  /** When this client sent it, to find it in the history after a reconnect. */
  createdAt: Date;
  /**
   * `failed` when the server refused it, the socket was down or closed, or no
   * echo came in 10 s. A failed message may still have reached the server.
   */
  status: "sending" | "failed";
  error?: string;
}

/**
 * Tells the user the server refused their chat edit or delete. `WSProvider`
 * sets it as `chatError`, and `ChatModal` shows it for a few seconds.
 */
export interface ChatError {
  /** Tells apart two errors with the same message. */
  id: number;
  message: string;
}

/**
 * Carries everything live but the chat and presence, for pages to lay over
 * what they fetched. `WSProvider` provides it through {@link WSContext}, and
 * components read it with `useWS`. Each `last*Event` field holds only the
 * latest event of its kind: a consumer reacts in an effect when one changes,
 * and an event that another replaces within the same render is missed. After a
 * reconnect, `connectionEpoch` tells pages to fetch what they missed.
 */
export interface WSContextValue {
  wsStatus: "connecting" | "connected" | "disconnected";
  /** Set while the socket is down, for the banner that says so. */
  wsErrorMessage: string | null;
  /**
   * Shows vote counts live. It holds, by dump id, the counts the server pushed
   * or this tab changed optimistically; a dump missing from it shows its
   * fetched `voteCount`.
   */
  voteCounts: Record<string, number>;
  /**
   * Marks the dumps this user upvoted, for their vote buttons. The server's
   * `welcome` resets it on every connection.
   */
  myVotes: Set<string>;
  /** As `voteCounts`, for comments. */
  likeCounts: Record<string, number>;
  /** As `myVotes`, for comments. */
  myLikes: Set<string>;
  /**
   * Shows new dumps on the index as they are posted, above the feed `Index`
   * fetched. It holds, newest first and at most 100, the ones the server
   * announced this session, which are public, and the ones this user posted,
   * which may be private.
   */
  recentDumps: Dump[];
  /**
   * Takes deleted dumps off every list at once. It holds the dumps deleted this
   * session, or made private by someone else; a dump made public again leaves
   * it.
   */
  deletedDumpIds: Set<string>;
  lastVoteEvent: VoteEvent | null;
  /**
   * Keeps a dump up to date in every list that shows it. It holds the dump as
   * its latest `dump_created` or `dump_updated` has it, and a list updates it
   * in place, or puts it back where it was.
   */
  lastDumpEvent: Dump | null;
  lastPlaylistEvent: PlaylistEvent | null;
  deletedPlaylistIds: Set<string>;
  lastCommentEvent: CommentEvent | null;
  lastUserEvent: UserEvent | null;
  /**
   * Drives the bell's badge. It comes from the `welcome`, then each new
   * notification counts it up.
   */
  unreadNotificationCount: number;
  /**
   * Makes the bell ring, and puts the notification on the notifications page
   * as it arrives.
   */
  lastNotification: Notification | null;
  /**
   * Tells pages to fetch again what they missed while the socket was down. It
   * goes up on each reconnect, never on the first connection.
   */
  connectionEpoch: number;
  /**
   * Keeps the Follow buttons right when the user follows or unfollows in
   * another tab. It goes up on every follow change, in any tab, and
   * `FollowProvider` fetches the follow status again.
   */
  followsVersion: number;
  /**
   * Upvotes a dump at once and sends `vote_cast`. The server's answer confirms
   * or reverts it, and so does a timeout of 5 s, which covers a closed socket.
   * `shownCount` is the count on screen, used when `voteCounts` has none yet.
   * Does nothing when the user already voted.
   */
  castVote: (dumpId: string, shownCount?: number) => void;
  /** Withdraws an upvote, as {@link WSContextValue.castVote} casts one. */
  removeVote: (dumpId: string, shownCount?: number) => void;
  /** Likes a comment, as {@link WSContextValue.castVote} upvotes a dump. */
  castCommentLike: (commentId: string, shownCount?: number) => void;
  /** Withdraws a like, as {@link WSContextValue.castVote} casts a vote. */
  removeCommentLike: (commentId: string, shownCount?: number) => void;
  /**
   * Shows a dump this user just posted on the index without waiting for its
   * broadcast, which a private dump never gets. `DumpCreateModal` calls it,
   * and it adds the dump to `recentDumps`.
   */
  injectDump: (dump: Dump) => void;
  /**
   * Zeroes the bell's count, once the notifications page has marked them read
   * on the server.
   */
  clearUnreadNotifications: () => void;
}

/**
 * Carries the chat's live side, which `ChatModal` lays over the history it
 * fetches and the chat buttons show as a badge. `WSProvider` provides it
 * through {@link WSChatContext}, and components read it with `useWSChat`. The
 * socket sends chat only to signed-in users, so for a visitor it stays empty.
 */
export interface WSChatContextValue {
  /**
   * Shows chat messages as they arrive. It holds the ones received this
   * session, at most 200, which `ChatModal` merges with the history it
   * fetches. A reconnect empties it while the chat is closed, since `ChatModal`
   * fetches everything again on open.
   */
  chatMessages: ChatMessage[];
  /**
   * Takes the messages deleted this session out of the history `ChatModal`
   * fetched.
   */
  deletedChatIds: Set<string>;
  /**
   * Drives the chat buttons' unread badge. It counts the messages from others
   * after the read marker, which the server keeps, so the count agrees across
   * tabs and devices.
   */
  unreadChatCount: number;
  /**
   * Places the "new" divider when the chat opens. It holds the time of the
   * newest message the user has seen, which the server keeps, and is null
   * until the `welcome`, and for a visitor.
   */
  chatReadAt: Date | null;
  pendingChatMessages: PendingChatMessage[];
  /** Only for edits and deletes. A failed send shows on its pending message. */
  chatError: ChatError | null;
  /**
   * Shows who is typing. It includes the user themselves, whom `ChatModal`
   * filters out.
   */
  typingUsers: OnlineUser[];
  /** Trims `body` and sends it as a pending message. Ignores a blank body. */
  sendChatMessage: (body: string, replyTo?: ChatReplyTarget) => void;
  retryChatMessage: (nonce: string) => void;
  discardChatMessage: (nonce: string) => void;
  /**
   * Sends the edit if the socket is open, else drops it. It shows once the
   * server broadcasts it, or fails as `chatError`.
   */
  editChatMessage: (id: string, body: string) => void;
  /** Sends the deletion if the socket is open, as `editChatMessage` does. */
  deleteChatMessage: (id: string) => void;
  dismissChatError: () => void;
  /**
   * Moves the read marker up to `at`, the time of the newest message seen. It
   * zeroes `unreadChatCount` at once and sends the marker at most once a
   * second. A marker set offline goes out with the next `welcome`.
   */
  markChatRead: (at: Date) => void;
  /**
   * Repairs the live buffer after a reconnect. It replaces its messages between
   * `from` and `to` with `messages`, which `ChatModal` fetched. A message
   * missing from them was deleted while the socket was down. A failed send
   * found among them did reach the server, and leaves the pending list.
   */
  reconcileChat: (messages: ChatMessage[], from: Date, to: Date) => void;
  /**
   * Tells the server whether the user is typing, when the socket is open.
   * `ChatModal` resends `true` every few seconds while typing continues, since
   * the server forgets a typer after 6 s.
   */
  setChatTyping: (typing: boolean) => void;
  /**
   * Spares the user a notification for a mention they read live. It tells the
   * server whether the chat is open in a visible tab; while it is, the server
   * sends no notification for a mention, and this client doesn't count the
   * message unread.
   */
  setChatOpen: (open: boolean) => void;
}

/**
 * Carries who is online, for `PresenceRow`. `WSProvider` provides it through
 * {@link WSPresenceContext}, and components read it with `useWSPresence`.
 */
export interface WSPresenceContextValue {
  /** The signed-in users with a socket open, each once. */
  onlineUsers: OnlineUser[];
}

/**
 * Lets a component render outside `WSProvider`, as if the socket were
 * connecting.
 */
export const defaultWSValue: WSContextValue = {
  wsStatus: "connecting",
  wsErrorMessage: null,
  voteCounts: {},
  myVotes: new Set(),
  likeCounts: {},
  myLikes: new Set(),
  recentDumps: [],
  deletedDumpIds: new Set(),
  lastVoteEvent: null,
  lastDumpEvent: null,
  lastPlaylistEvent: null,
  deletedPlaylistIds: new Set(),
  lastCommentEvent: null,
  lastUserEvent: null,
  unreadNotificationCount: 0,
  lastNotification: null,
  connectionEpoch: 0,
  followsVersion: 0,
  castVote: () => {},
  removeVote: () => {},
  castCommentLike: () => {},
  removeCommentLike: () => {},
  injectDump: () => {},
  clearUnreadNotifications: () => {},
};

/** Lets a component render outside `WSProvider`, with an empty chat. */
export const defaultWSChatValue: WSChatContextValue = {
  chatMessages: [],
  deletedChatIds: new Set(),
  unreadChatCount: 0,
  chatReadAt: null,
  pendingChatMessages: [],
  chatError: null,
  typingUsers: [],
  sendChatMessage: () => {},
  retryChatMessage: () => {},
  discardChatMessage: () => {},
  editChatMessage: () => {},
  deleteChatMessage: () => {},
  dismissChatError: () => {},
  markChatRead: () => {},
  reconcileChat: () => {},
  setChatTyping: () => {},
  setChatOpen: () => {},
};

/** Lets a component render outside `WSProvider`, with nobody online. */
export const defaultWSPresenceValue: WSPresenceContextValue = {
  onlineUsers: [],
};

/**
 * Carries the live state pages lay over what they fetched: the connection, the
 * votes and likes, and the latest event of each kind. Read it with `useWS`.
 */
export const WSContext: React.Context<WSContextValue> = createContext<
  WSContextValue
>(defaultWSValue);
/** Carries the chat's live stream and read state. Read it with `useWSChat`. */
export const WSChatContext: React.Context<WSChatContextValue> = createContext<
  WSChatContextValue
>(
  defaultWSChatValue,
);
/** Carries who is online. Read it with `useWSPresence`. */
export const WSPresenceContext: React.Context<WSPresenceContextValue> =
  createContext<
    WSPresenceContextValue
  >(
    defaultWSPresenceValue,
  );