index.js

const core = require('@actions/core')
const github = require('@actions/github')
const { IncomingWebhook } = require('@slack/webhook')
const parse = require('parse-diff')

function getAdditions (diff, fileToWatch) {
  const files = parse(diff)
  const additions = []
  files.filter(file => file.to.includes(fileToWatch.toLowerCase()))
    .forEach((file) => {
      file.chunks.forEach(chunk => {
        chunk.changes.filter(change => change.type === 'add')
          .forEach(change => {
            additions.push(change.content)
          })
      })
    })
  return additions
}

async function getPRDiff (githubToken) {
  const octoKit = github.getOctokit(githubToken)
  const { data: diff } = await octoKit.rest.pulls.get({
    repo: github.context.repo.repo,
    owner: github.context.repo.owner,
    pull_number: github.context.payload.pull_request.number,
    mediaType: { format: 'diff' }
  })
  return diff
}

async function notifySlack (slackChannel, slackWebhook, title, text) {
  const webhook = new IncomingWebhook(slackWebhook, {
    channel: slackChannel,
    username: title
  })
  await webhook.send({
    text: text
  })
}

function getInputs () {
  const fileToWatch = core.getInput('file', { required: true })
  const slackTitle = core.getInput('slack-title', { required: false })
  const slackChannel = core.getInput('slack-channel', { required: true })
  const slackWebhook = core.getInput('slack-webhook', { required: true })
  const githubToken = core.getInput('github-token', { required: true })
  const includePRLinkString = core.getInput('include-pr-link', { required: false })
  const includePRLink = includePRLinkString === 'true'
  const eventName = github.context.eventName
  return { fileToWatch, slackTitle, slackChannel, slackWebhook, githubToken, includePRLink, eventName }
}

function getTitle (slackTitle, fileToWatch) {
  if (slackTitle) {
    return slackTitle
  } else {
    return 'Additions to: ' + fileToWatch
  }
}

async function run () {
  try {
    const { fileToWatch, slackTitle, slackChannel, slackWebhook, githubToken, includePRLink, eventName } = getInputs()
    let didNotify
    if (eventName === 'pull_request') {
      const diff = await getPRDiff(githubToken)
      const additions = getAdditions(diff, fileToWatch)
      if (additions.length === 0) {
        console.log('No additions found')
        didNotify = false
      } else {
        console.log('Found ' + additions.length + '. Notifying channel: ' + slackChannel)
        const title = getTitle(slackTitle, fileToWatch)
        let text = additions.join('\r\n')
        if (includePRLink) {
          text += '\r\n \r\n' + github.context.payload.pull_request.html_url
        }
        await notifySlack(slackChannel, slackWebhook, title, text)
        didNotify = true
      }
    } else {
      didNotify = false
    }
    core.setOutput('didNotify', didNotify)
  } catch (error) {
    console.log(error)
    core.setFailed(error.message)
  }
}

(async () => {
  await run()
})()