name: Add changelog label to merged PR
on:
  pull_request:
    types: [closed]

jobs:
  build:
    if: github.event.pull_request.merged
    runs-on: ubuntu-latest
    steps:
      - name: Apply label
        uses: actions/github-script@0.4.0
        with:
          github-token: ${{secrets.GITHUB_TOKEN}}
          script: |
            const is_changelog_label = (label) => label.name.startsWith('Changelog Entry: ');
            if (context.payload.pull_request.labels.some(is_changelog_label)) {
                console.log('Issue already has Changelog Entry label, skipping...');
                return;
            }
            github.issues.addLabels({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              labels: ['Changelog Entry: Pending']
            });