// NodeJS script

const fs = require('fs/promises');
const fsConstants = require('fs').constants;
const path = require('path');
const {EOL} = require('os');

const http = require('http');
const handler = require('serve-handler');

const IDLENGTH = 36; // UUID v4

const port = process.env.DRAWIOPORT || 8700;
const stateDir = process.env.DRAWIOSTATEDIR || ".";

async function startServer() {
  const opsDir = path.join(stateDir, 'ops');
  const sessionDir = path.join(stateDir, 'sessions');
  try {
    process.stdout.write("Can read/write in directory '" + opsDir + "' ? ...");
    await fs.access(opsDir, fsConstants.R_OK | fsConstants.W_OK);
    process.stdout.write("OK" + EOL);
    process.stdout.write("Can read/write in directory '" + sessionDir + "' ? ...");
    await fs.access(sessionDir, fsConstants.R_OK | fsConstants.W_OK);
    process.stdout.write("OK" + EOL);
  } catch (e) {
    process.stdout.write(EOL + "Please make sure the following directories exist and are writable:" + EOL);
    process.stdout.write("  " + opsDir + EOL);
    process.stdout.write("  " + sessionDir + EOL);
    process.exit(1);
  }

  const { WebSocketServer } = require('ws');
  const { v4: uuidv4 } = require("uuid");

  function asyncSleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
  }

  const httpServer = http.createServer((request, response) => {
    // You pass two more arguments for config and middleware
    // More details here: https://github.com/vercel/serve-handler#options
    console.log(request.method, request.url)
    return handler(request, response);
  });

  const wsServer = new WebSocketServer({
    server: httpServer,
    path: "/websocket",
  });

  // Provides async reads and writes to files, while guaranteeing that for every file, a read always reads the latest write.
  class QueuedIO {
    constructor(path) {
      this.path = path;
      this.queues = new Map();
    }
    _queuedIO(f, filename, ...args) {
      const lastIO = this.queues.get(filename) || Promise.resolve();
      const nextIO = lastIO.then(() => f(path.join(this.path, filename), ...args));
      this.queues.set(filename, nextIO.catch(e => {/*console.log("silently caught", e)*/}));
      return nextIO;
    }
    write(filename, data) {
      // console.log("writing file", filename);
      return this._queuedIO((path, data) => fs.writeFile(path, data, {encoding: 'utf8'}), filename, data);
    }
    append(filename, data) {
      // console.log("appending to file", filename);
      const result = this._queuedIO(fs.appendFile, filename, data);
      // result.then(() => console.log("success")).catch(e => console.log("COULD NOT APPEND", e));
      return result;
    }
    stat(filename) {
      // console.log("statting file", filename);
      return this._queuedIO(fs.stat, filename);
    }
    read(filename) {
      // console.log("reading file", filename);
      return this._queuedIO(path => fs.readFile(path, {encoding:'utf8'}), filename);
    }
    writeJSON(filename, json) {
      // console.log("writeJSONing file", filename);
      return this.write(filename, JSON.stringify(json));
    }
    readJSON(filename) {
      // console.log("readJSONing file", filename);
      return this.read(filename).then(JSON.parse);
    }
  }

  // non-volatile state
  const opsDB = new QueuedIO(opsDir);
  const sessionDB = new QueuedIO(sessionDir);

  class Session {
    constructor(id) {
      this.id = id;
      this.users = new Set();
    }

    join(socket) {
      this.users.add(socket);
    }

    leave(socket) {
      this.users.delete(socket);
    }

    broadcast(json, skip) {
      if (json.type !== "update_cursor") {
        console.log("BROADCAST to", this.users.size-1, "subscribers...", json);
      }
      const stringified = JSON.stringify({type: "broadcast", sessionId: this.sessionId, msg: json});
      this.users.forEach((_, socket) => {
        if (socket !== skip) { // don't echo
          try {
            socket.send(stringified); // forward incoming request to all
          } catch (e) {
            console.log("Error:", e, "Closing socket...")
            socket.close(); // in case of an error, it is the client's responsibility to re-subscribe and 'catch up'.
          }
        }
      });
    }
  }

  // mapping of sessionId to Session
  const sessions = new Map();

  function getSession(id) {
    let session = sessions.get(id);
    if (session === undefined) {
      session = new Session(id);
      sessions.set(id, session);
    }
    return session;
  }

  const lockedCellsGlobal = new Set();

  wsServer.on('connection', (socket, req) => {
    const reqUrl = new URL(req.url, req.headers.origin);
    const myId = reqUrl.searchParams.get('me');
    console.log("Client connected.", myId);

    socket.sendJSON = function(json) {
      if (json.type !== "pong") {
        console.log("<-", json);
      }
      this.send(JSON.stringify(json));
    }

    function commonHandler(req) {
      if (req.type === "ping") {
        socket.sendJSON({type: "pong"});
        return true;
      }
    }

    class LeftHandler {
      async handle(req) {
        console.log("LeftHandler", req.type);
        if (commonHandler(req)) {
          console.log("PING");
          return this;
        }
        else if (req.type === "join") {
          const { reqId, sessionId, userId } = req;
          // Reply with all operations in session
          const session = await sessionDB.read(sessionId).catch(e => {
            if (e.code === 'ENOENT') {
              return ""; // Act as if session exists and is empty
            } else {
              throw e;
            }
          });
          const opIds = new Array(session.length / IDLENGTH);
          for (let i=0; i<opIds.length; i+=1) {
            const offset = i * IDLENGTH;
            opIds[i] = session.slice(offset, offset + IDLENGTH);
          }
          const ops = await Promise.all(opIds.map(async id => ({id, detail: await opsDB.readJSON(id)})));
          socket.sendJSON({type: "ack", reqId, ops});

          this.close();
          return new JoinedHandler(sessionId);
        }
        else if (req.type === "new_share") {
          console.log("HEY");
          const { reqId, ops } = req;
          const sessionId = uuidv4();
          await Promise.all(ops.map(({id, detail}) => opsDB.writeJSON(id, detail)));
          await sessionDB.write(sessionId, ops.map(op=>op.id).join(''));
          socket.sendJSON({type: "ack", reqId, sessionId});

          this.close();
          return new JoinedHandler(sessionId);
        }
        else {
          console.log("No handler for request:", req.type);
          return this;
        }
      }

      close() {}
    }

    class JoinedHandler {
      constructor(sessionId) {
        this.session = getSession(sessionId);
        this.lockedCells = new Set();
        this.session.join(socket);
      }

      async handle(req) {
        if (commonHandler(req)) {
          return this;
        }
        else if (req.type === "broadcast") {
          const { msg } = req;
          this.session.broadcast(msg, socket);
        }
        else if (req.type === "leave") {
          const { reqId } = req;
          socket.sendJSON({type: "ack", reqId});

          this.close();
          return new LeftHandler();
        }
        else if (req.type === "new_edit") {
          const { reqId, op: {id, detail} } = req;
          await opsDB.writeJSON(id, detail);
          await sessionDB.append(this.session.id, id); // Creates file if it doesn't exist yet
          // Best effort broadcast to all subscribers
          this.session.broadcast({type: "pub_edit", op: {id, detail}}, socket);
          // Send ACK
          socket.sendJSON({type: "ack", reqId});
        }
        else if (req.type === "request_lock") {
          const { reqId, cellIds } = req;
          let canLock = true;
          for (const cellId of cellIds) {
            if (lockedCellsGlobal.has(cellId)) {
              canLock = false;
              break;
            }
          }
          if (canLock) {
            for (const cellId of cellIds) {
              lockedCellsGlobal.add(cellId);
              this.lockedCells.add(cellId);
            }
          }
          socket.sendJSON({ type: "ack", reqId, success: canLock });
        }
        else if (req.type === "release_lock") {
          const { reqId, cellIds } = req;
          for (const cellId of cellIds) {
            if (this.lockedCells.has(cellId)) {
              lockedCellsGlobal.delete(cellId);
              this.lockedCells.delete(cellId);
            }
          }
        }
        else {
          console.log("No handler for request:", req.type);
        }
        return this;
      }

      close() {
        this.session.leave(socket);
        this.session.broadcast({type: "update_selection", userId: myId, selectedIds: []})
      }
    }

    let handlerPromise = Promise.resolve(new LeftHandler());
    function queuedHandler(req) {
      handlerPromise = handlerPromise.then(async handler => {
        try {
          return await handler.handle(req);
        } catch (e) {
          console.log("Error handling", req, e);
          return handler;
        }
      });
    }

    socket.on('message', function(data) {
      const req = JSON.parse(data);
      if (req.type !== "ping" && !(req.type === "broadcast" && req.msg.type === "update_cursor")) {
        console.log("->", req);
      }
      queuedHandler(req);
    });

    socket.on('close', function() {
      handlerPromise.then(h => h.close());
      console.log("Client disconnected.");
    })
  });

  httpServer.listen(port);
  console.log("Listening on", port);
}


startServer().catch(e => {
  console.log("Error in startServer:", e);
  process.exit(1);
});