text: // @flow
  import http from "http";
  import IO from "socket.io";
  import socketRedisAdapter from "socket.io-redis";
  import SocketAuth from "socketio-auth";
  import app from "./app";
  import { Document, Collection, View } from "./models";
  import policy from "./policies";
  import { client, subscriber } from "./redis";
  import { getUserForJWT } from "./utils/jwt";
  import { checkMigrations } from "./utils/startup";
  
  const server = http.createServer(app.callback());
  let io;
  
  const { can } = policy;
  
  io = IO(server, {
    path: "/realtime",
    serveClient: false,
    cookie: false,
  });
  
  io.adapter(
    socketRedisAdapter({
      pubClient: client,
      subClient: subscriber,
    })
  );
  
  io.of("/").adapter.on("error", (err) => {
    if (err.name === "MaxRetriesPerRequestError") {
      console.error(`Redis error: ${err.message}. Shutting down now.`);
      throw err;
    } else {
      console.error(`Redis error: ${err.message}`);
    }
  });
  
  SocketAuth(io, {
    authenticate: async (socket, data, callback) => {
      const { token } = data;
  
      try {
        const user = await getUserForJWT(token);
        socket.client.user = user;
  
        // store the mapping between socket id and user id in redis
        // so that it is accessible across multiple server nodes
        await client.hset(socket.id, "userId", user.id);
  
        return callback(null, true);
      } catch (err) {
        return callback(err);
      }
    },
    postAuthenticate: async (socket, data) => {
      const { user } = socket.client;
  
      // the rooms associated with the current team
      // and user so we can send authenticated events
      let rooms = [`team-${user.teamId}`, `user-${user.id}`];
  
      // the rooms associated with collections this user
      // has access to on connection. New collection subscriptions
      // are managed from the client as needed through the 'join' event
      const collectionIds = await user.collectionIds();
      collectionIds.forEach((collectionId) =>
        rooms.push(`collection-${collectionId}`)
      );
  
      // join all of the rooms at once
      socket.join(rooms);
  
      // allow the client to request to join rooms
      socket.on("join", async (event) => {
        // user is joining a collection channel, because their permissions have
        // changed, granting them access.
        if (event.collectionId) {
          const collection = await Collection.scope({
            method: ["withMembership", user.id],
          }).findByPk(event.collectionId);
  
          if (can(user, "read", collection)) {
            socket.join(`collection-${event.collectionId}`);
          }
        }
  
        // user is joining a document channel, because they have navigated to
        // view a document.
        if (event.documentId) {
          const document = await Document.findByPk(event.documentId, {
            userId: user.id,
          });
  
          if (can(user, "read", document)) {
            const room = `document-${event.documentId}`;
  
            await View.touch(event.documentId, user.id, event.isEditing);
            const editing = await View.findRecentlyEditingByDocument(
              event.documentId
            );
  
            socket.join(room, () => {
              // let everyone else in the room know that a new user joined
              io.to(room).emit("user.join", {
                userId: user.id,
                documentId: event.documentId,
                isEditing: event.isEditing,
              });
  
              // let this user know who else is already present in the room
              io.in(room).clients(async (err, sockets) => {
                if (err) throw err;
  
                // because a single user can have multiple socket connections we
                // need to make sure that only unique userIds are returned. A Map
                // makes this easy.
                let userIds = new Map();
                for (const socketId of sockets) {
                  const userId = await client.hget(socketId, "userId");
                  userIds.set(userId, userId);
                }
                socket.emit("document.presence", {
                  documentId: event.documentId,
                  userIds: Array.from(userIds.keys()),
                  editingIds: editing.map((view) => view.userId),
                });
              });
            });
          }
        }
      });
  
      // allow the client to request to leave rooms
      socket.on("leave", (event) => {
        if (event.collectionId) {
          socket.leave(`collection-${event.collectionId}`);
        }
        if (event.documentId) {
          const room = `document-${event.documentId}`;
          socket.leave(room, () => {
            io.to(room).emit("user.leave", {
              userId: user.id,
              documentId: event.documentId,
            });
          });
        }
      });
  
      socket.on("disconnecting", () => {
        const rooms = Object.keys(socket.rooms);
  
        rooms.forEach((room) => {
          if (room.startsWith("document-")) {
            const documentId = room.replace("document-", "");
            io.to(room).emit("user.leave", {
              userId: user.id,
              documentId,
            });
          }
        });
      });
  
      socket.on("presence", async (event) => {
        const room = `document-${event.documentId}`;
  
        if (event.documentId && socket.rooms[room]) {
          const view = await View.touch(
            event.documentId,
            user.id,
            event.isEditing
          );
          view.user = user;
  
          io.to(room).emit("user.presence", {
            userId: user.id,
            documentId: event.documentId,
            isEditing: event.isEditing,
          });
        }
      });
    },
  });
  
  server.on("error", (err) => {
    throw err;
  });
  
  server.on("listening", () => {
    const address = server.address();
    console.log(`\n> Listening on http://localhost:${address.port}\n`);
  });
  
  (async () => {
    await checkMigrations();
    server.listen(process.env.PORT || "3000");
  })();
  
  export const socketio = io;
  
  export default server;
  