app.js

const Y = require("yjs")
require("y-memory")(Y)
require("y-map")(Y)
require("y-array")(Y)
require("./y-webrtc")(Y)

const uuidv4 = require("uuid/v4")
const { line, curveBasis } = require("d3")

Y({
  db: {
    name: "memory",
  },
  connector: {
    name: "webrtc",
    host: "localhost",
    port: 3000,
    path: "/api",
  },
  share: {
    drawing: "Map",
  },
}).then((y) => {
  const userIDElem = document.getElementById("user-id")
  const peerIDElem = document.getElementById("peer-id")
  const peerButton = document.getElementById("peer-connect")
  const connectedP = document.getElementById("connected-peers")

  userIDElem.value = y.db.userId

  y.connector.onUserEvent(function(event) {
    switch (event.action) {
      case "userID":
        userIDElem.value = event.id
        break
      case "userJoined":
        var peerElem = document.createElement("li")
        peerElem.innerHTML = event.user
        connectedP.appendChild(peerElem)
        break
      case "userLeft":
        for (var peer of connectedP.children) {
          if (peer.innerHTML == event.user) {
            connectedP.removeChild(peer)
          }
        }
        break
    }
  })

  peerButton.onclick = function() {
    const peerID = peerIDElem.value

    if (peerID == "") {
      return
    }

    y.connector.connectToPeer(peerID)

    peerIDElem.value = ""
  }

  const whiteboard = document.getElementById("whiteboard")

  var painting = false
  var paths = new Map()
  var pathID

  function createOrUpdatePath(uid, points) {
    const lineFn = line()
      .x((d) => d[0])
      .y((d) => d[1])
      .curve(curveBasis)

    var path = paths.get(uid)

    if (path === undefined) {
      path = document.createElementNS("http://www.w3.org/2000/svg", "path")

      path.setAttribute("stroke", "blue")
      path.setAttribute("stroke-width", 3)
      path.setAttribute("fill", "none")
      path.setAttribute("pointer-events", "none")

      whiteboard.appendChild(path)

      paths.set(uid, path)
    }

    points = points.toArray().filter((point) => point !== undefined)

    if (points.length <= 0) {
      path.removeAttribute("d")

      return path
    }

    path.setAttribute("d", lineFn(points))

    return path
  }

  whiteboard.onmousedown = function(e) {
    painting = true

    const mouse = {
      x: e.offsetX,
      y: e.offsetY,
    }

    pathID = uuidv4()

    const sharedPath = y.share.drawing.set(pathID, Y.Array)
    sharedPath.push([[mouse.x, mouse.y]])
  }

  whiteboard.onmouseup = function() {
    painting = false
  }

  whiteboard.onmousemove = function(e) {
    const mouse = {
      x: e.offsetX,
      y: e.offsetY,
    }

    if (painting) {
      const sharedPath = y.share.drawing.get(pathID)
      sharedPath.push([[mouse.x, mouse.y]])
    }
  }

  y.share.drawing.observe(function(lineEvent) {
    const lineID = lineEvent.name

    switch (lineEvent.type) {
      case "add":
        createOrUpdatePath(lineID, lineEvent.value)

        lineEvent.value.observe(function(pointEvent) {
          switch (pointEvent.type) {
            case "insert":
              createOrUpdatePath(lineID, pointEvent.object)
              break
          }
        })

        break
    }
  })
})