Github app start

app/api/package.json

@@ -3,6 +3,8 @@
   "version": "0.0.0",
   "private": true,
   "dependencies": {
+    "@octokit/app": "^12.0.2",
+    "@octokit/webhooks-types": "^3.71.1",
     "@redwoodjs/api": "^0.31.0",
     "@redwoodjs/api-server": "^0.31.0",
     "cloudinary": "^1.23.0"

app/api/src/functions/githubhook.ts

@@ -0,0 +1,75 @@
+/* for local development
+Install and run smee (point at this function)
+```
+yarn global add smee-client
+smee --url https://smee.io/3zgDJiGO8TW7nvf --path /.netlify/functions/event_handler --port 8910
+```
+*/
+
+import { createHmac } from 'crypto'
+import { App } from '@octokit/app'
+import type { Endpoints } from '@octokit/types'
+import type { PullRequestEvent } from '@octokit/webhooks-types'
+
+const app = new App({
+  privateKey: process.env.GITHUB_APP_PRIVATE_KEY,
+  appId: process.env.GITHUB_APP_ID,
+  webhooks: {
+    secret: process.env.GITHUB_APP_SECRET,
+  },
+})
+
+const signRequestBody = (secret: string, body: string): string =>
+  'sha256=' + createHmac('sha256', secret).update(body, 'utf-8').digest('hex')
+
+const writePullRequestComment = async ({
+  event,
+  message,
+}: {
+  event: PullRequestEvent
+  message: string
+}): Promise<
+  Endpoints['POST /repos/{owner}/{repo}/issues/{issue_number}/comments']['response']
+> => {
+  const octokit = await app.getInstallationOctokit(event.installation.id)
+  return octokit.request(
+    'POST /repos/{owner}/{repo}/issues/{issue_number}/comments',
+    {
+      owner: event.repository.owner.login,
+      repo: event.repository.name,
+      issue_number: event.number,
+      body: message,
+    }
+  )
+}
+
+export const handler = async (req: {
+  body: string
+  headers: {
+    'x-hub-signature-256': string
+    'x-github-event': string
+  }
+}) => {
+  const theirSignature = req.headers['x-hub-signature-256']
+  const ourSignature = signRequestBody(process.env.GITHUB_APP_SECRET, req.body)
+  if (theirSignature !== ourSignature) {
+    return {
+      statusCode: 401,
+      body: 'Bad signature',
+    }
+  }
+  const eventType = req.headers['x-github-event']
+  if (eventType !== 'pull_request') {
+    return { statusCode: 200 }
+  }
+  const event: PullRequestEvent = JSON.parse(req.body)
+  if (['reopened', 'opened'].includes(event.action)) {
+    await writePullRequestComment({
+      event,
+      message: 'Salutations, what a fine PR you have here.',
+    })
+  }
+  return {
+    statusCode: 200,
+  }
+}