Try to find a comment to edit before creating

lib/github-comment.js

@@ -1,16 +1,61 @@
 'use strict'
 
 const githubClient = require('./github-client')
+const GQL = require('./github-graphql-client')
+
+const getPRComments = `query getPRComments($owner: String!, $repo: String!, $number: Int!, $cursor: String){
+  repository(owner: $owner, name:  $repo) {
+    pullRequest(number: $number) {
+      comments(first: 20, after:$cursor) {
+        nodes {
+          id
+          body
+          viewerDidAuthor
+        }
+        pageInfo {
+          endCursor
+          hasNextPage
+        }
+      }
+      labels(first: 15) {
+        nodes {
+          name
+        }
+      }
+    }
+  }
+}`
+
+function graphQlIdToRestId (nodeId) {
+  const decoded = Buffer.from(nodeId, 'base64').toString()
+  return decoded.match(/\d+$/)[0]
+}
+
+exports.getFirstBotComment = function getFirstBotComment ({ owner, repo, number }, cursor = null) {
+  return GQL(getPRComments, { owner, repo, number, cursor }).then(data => {
+    const { nodes, pageInfo } = data.repository.pullRequest.comments
+    const firstBotComment = nodes.find(e => e.viewerDidAuthor)
+    if (firstBotComment) {
+      return firstBotComment
+    }
+    if (pageInfo.hasNextPage) {
+      return exports.getFirstBotComment({ owner, repo, number }, pageInfo.endCursor)
+    }
+    return null
+  })
+}
 
 exports.createPrComment = function createPrComment ({ owner, repo, number, logger }, body) {
-  githubClient.issues.createComment({
-    owner,
-    repo,
-    number,
-    body
-  }, (err) => {
-    if (err) {
-      logger.error(err, 'Error while creating comment on GitHub')
+  exports.getFirstBotComment({ owner, repo, number, logger }).then((comment) => {
+    if (comment) {
+      const { id: nodeId, body: oldBody } = comment
+      const newBody = `${oldBody}\n${body}`
+      const id = graphQlIdToRestId(nodeId)
+      return githubClient.issues.editComment({ owner, repo, id, body: newBody })
     }
+    return githubClient.issues.createComment({ owner, repo, number, body })
+  }).catch((err) => {
+    logger.error(err, 'Error while creating comment on GitHub')
+    // swallow error
   })
 }

lib/github-graphql-client.js

@@ -0,0 +1,10 @@
+'use strict'
+
+const GitHubGQL = require('@octokit/graphql').defaults({
+  headers: {
+    'user-agent': 'Node.js GitHub Bot v1.0-beta',
+    authorization: 'token ' + (process.env.GITHUB_TOKEN || 'invalid-placeholder-token')
+  }
+})
+
+module.exports = GitHubGQL