Skeleton of resolving and applying labels copy-pasted from github-bot (…

…#1)

With a few tweaks related to:

- Logging: using `@actions/core` methods like `core.debug()` instead of
		   `bunyan` like the github-bot has been using
- GitHub Client: using `@actions/github` which is more or less exactly
			     what the github-bot also used, namely the
			     `oktokit/rest.js` package, it has just been pieced
			     together to be more convenient for GitHub Actions code

Other than that, it's copy-pasting of what was found in the github-bot
project:

- `./lib/node-repo.js`
- `./lib/node-labels.js` (renamed to `resolve-labels.js`)

..removing code that was not related to resolving & applying labels, along
with the related tests.

Currently this is *not* to be considered a GitHub Action, it's only the
said files from github-bot, adjusted slightly to the `@actions/*`
packages as a precursor to adding GitHub Action artifacts like
`action.yml` and so on.

Copied from this specific point in time: [nodejs/github-bot 737094](https://github.com/nodejs/github-bot/tree/737094cf07224be73eafa279356fd44a1cc55c87)

.github/workflows/test.yml

@@ -0,0 +1,20 @@
+name: Test
+
+on: [push, pull_request]
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [14.x, 15.x]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup Node.js
+        uses: actions/setup-node@v2.1.2
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm ci
+      - run: npm test

.gitignore

@@ -0,0 +1,7 @@
+node_modules
+npm-debug.log
+
+.DS_Store
+.env
+.vscode
+.nyc_output

lib/github-client.js

@@ -0,0 +1,8 @@
+'use strict'
+
+const github = require('@actions/github')
+const core = require('@actions/core')
+
+const token = core.getInput('repo-token', { required: true })
+
+module.exports = github.getOctokit(token)

lib/node-repo.js

@@ -0,0 +1,133 @@
+'use strict'
+
+/* eslint-disable camelcase */
+
+const core = require('@actions/core')
+const LRU = require('lru-cache')
+const Aigle = require('aigle')
+
+const githubClient = require('./github-client')
+const resolveLabels = require('./resolve-labels')
+const existingLabelsCache = new LRU({ max: 1, maxAge: 1000 * 60 * 60 })
+
+const fiveSeconds = 5 * 1000
+
+const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms))
+
+async function deferredResolveLabelsThenUpdatePr (options) {
+  const timeoutMillis = (options.timeoutInSec || 0) * 1000
+  await sleep(timeoutMillis)
+  return resolveLabelsThenUpdatePr(options)
+}
+
+async function resolveLabelsThenUpdatePr (options) {
+  const times = options.retries || 5
+  const interval = options.retryInterval || fiveSeconds
+  const retry = fn => Aigle.retry({ times, interval }, fn)
+
+  const filepathsChanged = await retry(() => listFiles({
+    owner: options.owner,
+    repo: options.repo,
+    pull_number: options.prId
+  }))
+  core.debug('Fetching PR files for labelling')
+
+  const resolvedLabels = resolveLabels(filepathsChanged, options.baseBranch)
+
+  return fetchExistingThenUpdatePr(options, resolvedLabels)
+}
+
+async function fetchExistingThenUpdatePr (options, labels) {
+  try {
+    const existingLabels = await fetchExistingLabels(options)
+    const labelsToAdd = stringsInCommon(existingLabels, labels)
+    core.debug('Resolved labels: ' + labels)
+    core.debug('Resolved labels to add: ' + labelsToAdd)
+    core.debug('Resolved existing labels: ' + existingLabels)
+
+    return updatePrWithLabels(options, labelsToAdd)
+  } catch (err) {
+    core.error('Error retrieving existing repo labels: ' + err)
+
+    return updatePrWithLabels(options, labels)
+  }
+}
+
+async function updatePrWithLabels (options, labels) {
+  // no need to request github if we didn't resolve any labels
+  if (!labels.length) {
+    return
+  }
+
+  core.debug('Trying to add labels: ' + labels)
+
+  try {
+    await githubClient.issues.addLabels({
+      owner: options.owner,
+      repo: options.repo,
+      issue_number: options.prId,
+      labels: labels
+    })
+
+    core.info('Added labels: ' + labels)
+  } catch (err) {
+    core.error('Error while adding labels: ' + err)
+  }
+}
+
+async function fetchExistingLabels (options) {
+  const cacheKey = `${options.owner}:${options.repo}`
+
+  if (existingLabelsCache.has(cacheKey)) {
+    return existingLabelsCache.get(cacheKey)
+  }
+
+  const labelsResult = await fetchLabelPages(options, 1)
+  const existingLabels = labelsResult.data || labelsResult || []
+  const existingLabelNames = existingLabels.map((label) => label.name)
+
+  // cache labels so we don't have to fetch these *all the time*
+  existingLabelsCache.set(cacheKey, existingLabelNames)
+  core.debug('Filled existing repo labels cache: ' + existingLabelNames)
+
+  return existingLabelNames
+}
+
+async function fetchLabelPages (options) {
+  // the github client API is somewhat misleading,
+  // this fetches *all* repo labels not just for an issue
+  const listLabelsOptions = await githubClient.issues.listLabelsForRepo.endpoint.merge({
+    owner: options.owner,
+    repo: options.repo,
+    per_page: 100
+  })
+
+  return await githubClient.paginate(listLabelsOptions)
+}
+
+function stringsInCommon (arr1, arr2) {
+  const loweredArr2 = arr2.map((str) => str.toLowerCase())
+  // we want the original string cases in arr1, therefore we don't lowercase them
+  // before comparing them cause that would wrongly make "V8" -> "v8"
+  return arr1.filter((str) => loweredArr2.indexOf(str.toLowerCase()) !== -1)
+}
+
+async function listFiles ({ owner, repo, pull_number }) {
+  try {
+    const response = await githubClient.pulls.listFiles({
+      owner,
+      repo,
+      pull_number
+    })
+    return response.data.map(({ filename }) => filename)
+  } catch (err) {
+    core.error('Error retrieving files from GitHub: ' + err)
+    throw err
+  }
+}
+
+exports.fetchExistingThenUpdatePr = fetchExistingThenUpdatePr
+exports.resolveLabelsThenUpdatePr = deferredResolveLabelsThenUpdatePr
+
+// exposed for testability
+exports._fetchExistingLabels = fetchExistingLabels