name: Lower null checks

on:
  pull_request:

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

jobs:
  build:
    runs-on: ubuntu-latest
    env:
      MAIN_BRANCH: main

    strategy:
      matrix:
        node-version: [16.x]

    steps:
      - name: Checkout current branch
        uses: actions/checkout@v3
        with:
          path: current
      - name: Checkout main branch
        uses: actions/checkout@v3
        with:
          ref: ${{ env.MAIN_BRANCH }}
          path: main
      - name: Use Node.js ${{ matrix.node-version }}
        uses: actions/setup-node@v3
        with:
          node-version: ${{ matrix.node-version }}
          cache: 'yarn'
          cache-dependency-path: |
            current/yarn.lock
            main/yarn.lock
      - name: Compare errors if enabling strictNullChecks
        env:
          URL: ${{ github.event.pull_request.comments_url }}
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          comment () {
            curl -X POST $URL \
              -H "Content-Type: application/json" \
              -H "Authorization: token $GITHUB_TOKEN" \
              --data "{ \"body\": \"${1}\" }"
          }

          sed -i 's/\/\/\s*"strictNullChecks":\s*true,/"strictNullChecks": true,/' "current/tsconfig.json"
          sed -i 's/\/\/\s*"strictNullChecks":\s*true,/"strictNullChecks": true,/' "main/tsconfig.json"

          yarn --mutex network --cwd ./current 2> .stderr-current > .out-current &
          pid1=$!
          
          yarn --mutex network --cwd ./main 2> .stderr-main  > .out-main &
          pid2=$!

          # wait for the processes that are expected to fail
          set +e
          wait $pid1
          wait $pid2
          set -e

          CURRENT=$(grep "Found [0-9]* errors" .out-current | sed 's/Found \(.*\) errors in .* files./\1/')
          MAIN=$(grep "Found [0-9]* errors" .out-main | sed 's/Found \(.*\) errors in .* files./\1/')

          if [ $CURRENT -gt $MAIN ]; then
            comment "After enabling [\`strictNullChecks\`](https://www.typescriptlang.org/tsconfig#strictNullChecks) this PR would be **increasing** the number of null check errors from ${MAIN} to ${CURRENT}. <br /> Make sure your branch is up-to-date with ${MAIN_BRANCH} and **check the diff in the console output** to gather more details."
            diff .out-current .out-main
            exit 1
          else
            echo "The PR has $CURRENT null check errors against $MAIN in main. You're good to go!"
          fi