feat: detect WIP commit messages (#32)

thanks @Raul6469 & @HeeL

lib/handle-pull-request-change.js

@@ -1,17 +1,29 @@
 module.exports = handlePullRequestChange
 
 async function handlePullRequestChange (robot, context) {
-  const title = context.payload.pull_request.title
-  const isWip = /\b(wip|do not merge)\b/i.test(title)
+  const {title, html_url, head} = context.payload.pull_request
+  const isWip = containsWIP(title) || await commitsContainWIP(context)
   const status = isWip ? 'pending' : 'success'
 
-  console.log(`Updating PR "${title}" (${context.payload.pull_request.html_url}): ${status}`)
+  console.log('Updating PR "%s" (%s): %s', title, html_url, status)
 
   context.github.repos.createStatus(context.repo({
-    sha: context.payload.pull_request.head.sha,
+    sha: head.sha,
     state: status,
     target_url: 'https://github.com/apps/wip',
     description: isWip ? 'work in progress – do not merge!' : 'ready for review',
     context: 'WIP'
   }))
 }
+
+async function commitsContainWIP (context) {
+  const commits = await context.github.pullRequests.getCommits(context.repo({
+    number: context.payload.pull_request.number
+  }))
+
+  return commits.data.map(element => element.commit.message).some(containsWIP)
+}
+
+function containsWIP (string) {
+  return /\b(wip|do not merge)\b/i.test(string)
+}