name: Label PR version

# Contributors (especially from forks) can't set labels themselves — that needs
# triage rights. A PR's version line is fully determined by its base branch, so
# this reads base.ref and applies v1/v2 on their behalf. pull_request_target runs
# in the base repo's context so it has write access even for fork PRs; it only
# reads trusted metadata (the base ref) and never checks out or runs PR code.
on:
  pull_request_target:
    types: [opened, reopened, edited]

permissions:
  pull-requests: write

concurrency:
  group: pr-version-${{ github.event.pull_request.number }}
  cancel-in-progress: true

jobs:
  label:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/github-script@v9
        with:
          script: |
            const base = context.payload.pull_request.base.ref;
            const label = base === 'v1' ? 'v1'
                        : base === 'main-v2' ? 'v2'
                        : null;
            if (!label) {
              core.info(`Base branch '${base}' isn't a release line; skipping.`);
              return;
            }
            const other = label === 'v2' ? 'v1' : 'v2';
            await github.rest.issues.addLabels({
              ...context.repo,
              issue_number: context.payload.pull_request.number,
              labels: [label],
            });
            // Drop the other line's label if the base was changed after opening.
            try {
              await github.rest.issues.removeLabel({
                ...context.repo,
                issue_number: context.payload.pull_request.number,
                name: other,
              });
            } catch (e) {
              core.info(`No ${other} label to remove.`);
            }