fix connection time syncing handling

Share the time syncing code, and while we're at it wrap the whole
connection thing in a class.  Makes it easier to pass the connection
around & later on add more advanced handler registration if we want to.

public/shared.js

@@ -105,11 +105,58 @@ export function session_id() {
   return match ? match[1] : null
 }
 
-/**
- * Guess the exact current server time.
- */
-export function servertime_now_ns() {
-  const now_ms = performance.now()
-  const delta_ns = ms_ns * (now_ms - toffset_ms)
-  return servertime + delta_ns
+export class Connection {
+  constructor() {
+    this.socket = null
+    this.toffset_ms = null
+    this.servertime = null
+    this.handlers = {
+      time: this._handler_time.bind(this),
+      error: this._handler_error.bind(this),
+    }
+  }
+
+  _handler_time({ value: { time } }) {
+    this.servertime = time
+    this.toffset_ms = performance.now()
+  }
+
+  _handler_error({ value: { reason } }) {
+    console.error(`Error: ${reason}`)
+  }
+
+  connect(url) {
+    this.socket = new WebSocket(url)
+    this.socket.addEventListener("open", (event) => {
+      if ("helo" in this.handlers) {
+        this.handlers["helo"](event)
+      }
+    })
+    this.socket.addEventListener("message", (event) => {
+      const msg = JSON.parse(event.data)
+      if (msg.type in this.handlers) {
+        this.handlers[msg.type](msg)
+      } else {
+        console.error(`Unhandled message: ${event.data}`)
+      }
+    })
+  }
+
+  on(type, callback) {
+    this.handlers[type] = callback
+  }
+
+  /**
+   * Guess the exact current server time.
+   */
+  servertime_now_ns() {
+    const now_ms = performance.now()
+    const delta_ns = ms_ns * (now_ms - this.toffset_ms)
+    return this.servertime + delta_ns
+  }
+
+  send(type, value) {
+    // console.debug('sending', value)
+    this.socket.send(JSON.stringify({ type, value }))
+  }
 }