name: Close PR on README.md change

on:
  pull_request:
    types: [edited]

jobs:
  close_pr:
    runs-on: ubuntu-latest
    steps:
    - name: Check out code
      uses: actions/checkout@v2
    - name: Check for README.md changes
      run: |
        if git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} | grep -q "^README.md$"; then
          echo "README.md has been modified. Closing the PR."
          curl -X PATCH -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" -d '{"state":"closed"}' "https://api.github.com/repos/${{ github.repository }}/pulls/${{ github.event.pull_request.number }}"
        else
          echo "No changes to README.md. Nothing to do."
        fi
      env:
        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}