feat: add support for slack private groups

the package slackbots distinguishes channels from private groups in its
API, so this commit refactors the code to support both channels and
groups and use the correct api method for each.

app.json

@@ -25,6 +25,10 @@
       "description": "Slack channels to post the announcements, comma separated",
       "value": ""
     },
+    "SLACK_GROUPS": {
+      "description": "Slack private groups to post the announcements, comma separated",
+      "value": ""
+    },
     "CHECK_INTERVAL": {
       "description": "Time interval to check for new pull requests, in milliseconds",
       "value": "3600000"

lib/server.js

@@ -3,22 +3,24 @@ const pullhub = require('pullhub')
 const debounce = require('lodash.debounce')
 
 module.exports = function server () {
-  const requiredEnvs = ['SLACK_TOKEN', 'GH_TOKEN', 'SLACK_CHANNELS', 'GH_REPOS']
+  const env = process.env
+  const requiredEnvs = ['SLACK_TOKEN', 'GH_TOKEN', 'GH_REPOS']
 
-  if (!requiredEnvs.every((k) => !!process.env[k])) {
+  if (!requiredEnvs.every((k) => !!env[k])) {
     throw (
       new Error('Missing one of this required ENV vars: ' + requiredEnvs.join(','))
     )
   }
 
-  const channels = process.env.SLACK_CHANNELS.split(',') || []
-  const repos = process.env.GH_REPOS.split(',') || []
-  const labels = process.env.GH_LABELS
-  const checkInterval = process.env.CHECK_INTERVAL || 3600000 // 1 hour default
+  const channels = env.SLACK_CHANNELS ? env.SLACK_CHANNELS.split(',') : []
+  const groups = env.SLACK_GROUPS ? env.SLACK_GROUPS.split(',') : []
+  const repos = env.GH_REPOS ? env.GH_REPOS.split(',') : []
+  const labels = env.GH_LABELS
+  const checkInterval = env.CHECK_INTERVAL || 3600000 // 1 hour default
 
   const bot = new Slackbot({
-    token: process.env.SLACK_TOKEN,
-    name: process.env.SLACK_BOT_NAME || 'PR-Police'
+    token: env.SLACK_TOKEN,
+    name: env.SLACK_BOT_NAME || 'PR-Police'
   })
 
   bot.on('start', () => {
@@ -49,5 +51,9 @@ module.exports = function server () {
     channels.map((channel) => {
       bot.postMessageToChannel(channel, message)
     })
+
+    groups.map((group) => {
+      bot.postMessageToGroup(group, message)
+    })
   }
 }