add eventWrapper not tested

lib/constants.json

@@ -16,11 +16,18 @@
     "contractFilesChanged": "contractFilesChanged",
     "contractConfigChanged": "contractConfigChanged"
   },
+  "process": {
+    "log": "log",
+    "events": {
+      "on": "on",
+      "request": "request",
+      "response": "response"
+    }
+  },
   "pipeline": {
     "init": "init",
     "build": "build",
     "initiated": "initiated",
-    "built": "built",
+    "built": "built"
-    "log": "log"
   }
 }

lib/pipeline/pipeline.js

@@ -79,7 +79,7 @@ class Pipeline {
                         return next(msg.error);
                       }
 
-                      if (msg.result === constants.pipeline.log) {
+                      if (msg.result === constants.process.log) {
                         if (self.logger[msg.type]) {
                           return self.logger[msg.type](self.normalizeInput(msg.message));
                         }

lib/pipeline/webpackProcess.js

@@ -4,7 +4,7 @@ const utils = require('../utils/utils');
 const fs = require('../core/fs');
 const constants = require('../constants');
 const HardSourceWebpackPlugin = require('hard-source-webpack-plugin');
-const ProcessWrapper = require('../core/processWrapper');
+const ProcessWrapper = require('../process/processWrapper');
 
 let webpackProcess;
 

lib/process/eventsWrapper.js

@@ -0,0 +1,48 @@
+const constants = require('../constants');
+
+class Events {
+  constructor() {
+    this.eventId = 0;
+    this.subscribedEvents = {};
+    this.listenToParentProcess();
+  }
+
+  listenToParentProcess() {
+    process.on('message', (msg) => {
+      if (!msg.event || msg.event !== constants.process.events.response) {
+        return;
+      }
+      if (!this.subscribedEvents[msg.eventId]) {
+        return;
+      }
+      this.subscribedEvents[msg.eventId](msg.result);
+    });
+  }
+
+  sendEvent() {
+    const eventType = arguments[0];
+    const requestName = arguments[1];
+
+    let args = [].slice.call(arguments, 2);
+    this.eventId++;
+    this.subscribedEvents[this.eventId] = args[args.length - 1];
+    args = args.splice(0, args.length - 2);
+
+    process.send({
+      event: eventType,
+      requestName,
+      args,
+      eventId: this.eventId
+    });
+  }
+
+  on() {
+    this.sendEvent(constants.process.events.on, ...arguments);
+  }
+
+  request() {
+    this.sendEvent(constants.process.events.request, ...arguments);
+  }
+}
+
+module.exports = Events;

lib/process/processWrapper.js

@@ -30,7 +30,7 @@ class ProcessWrapper {
     if (messages[0].indexOf('hard-source')) {
       return;
     }
-    process.send({result: constants.pipeline.log, message: messages, type});
+    process.send({result: constants.process.log, message: messages, type});
   }
 }