name: Backport merged pull request
on:
  issue_comment:
    types: [created]
permissions:
  contents: write # for comment creation on original PR
  pull-requests: write
jobs:
  backport:
    name: Backport pull request
    runs-on: ubuntu-latest

    # Only run when the comment starts with the `/backport` command on a PR and
    # the commenter has write access to the repository. We do not want to allow
    # everybody to trigger backports and create branches in our repository.
    if: >
        github.event.issue.pull_request &&
        startsWith(github.event.comment.body, '/backport ') &&
        (
        github.event.comment.author_association == 'OWNER' ||
        github.event.comment.author_association == 'COLLABORATOR' ||
        github.event.comment.author_association == 'MEMBER'
        )
    steps:
      - uses: actions/checkout@v4
      - name: Get backport metadata
        # the target branch is the first argument after `/backport`
        run: |
          set -euo pipefail
          body="${{ github.event.comment.body }}"
          
          line=${body%%$'\n'*} # Get the first line
          if [[ $line =~ ^/backport[[:space:]]+([^[:space:]]+) ]]; then
            echo "BACKPORT_TARGET=${BASH_REMATCH[1]}" >> "$GITHUB_ENV"
          else
            echo "Usage: /backport <target-branch>" >&2
            exit 1
          fi

      - name: Create backport pull request
        uses: korthout/backport-action@v4
        with:
          add_labels: 'backport'
          copy_labels_pattern: '.*'
          label_pattern: ''
          target_branches: ${{ env.BACKPORT_TARGET }}