name: Propagate auto-merge label to backports

on:
  pull_request:
    types: [opened]

jobs:
  propagate-label:
    runs-on: ubuntu-latest

    permissions:
      pull-requests: write
      issues: write

    steps:
      - name: Detect backport and original PR (metadata)
        id: extract
        uses: actions/github-script@v8
        with:
          script: |
            const pr = context.payload.pull_request;
            const base = pr.base.ref;
            if (!/^version-(15|16)-hotfix$/.test(base)) {
              core.setOutput('is_backport', 'false');
              return;
            }

            const isMergify = pr.user && pr.user.login === 'mergify[bot]';
            const headRef = pr.head.ref || '';
            const match = headRef.match(/(?:^|\/)pr-(\d+)(?:-|$)/i);

            if (isMergify && match) {
              const original = Number(match[1]);
              if (!Number.isNaN(original)) {
                core.setOutput('original_pr', String(original));
                core.setOutput('is_backport', 'true');
                return;
              }
            }

            core.setOutput('is_backport', 'false');

      - name: Check original PR labels
        if: steps.extract.outputs.is_backport == 'true'
        id: check
        uses: actions/github-script@v7
        with:
          script: |
            const prNumber = Number("${{ steps.extract.outputs.original_pr }}");

            const { data } = await github.rest.issues.get({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: prNumber
            });

            const labels = data.labels.map(l => l.name);
            core.setOutput("has_auto_merge", labels.includes("auto-merge backports"));

      - name: Add auto-merge label to backport PR
        if: steps.check.outputs.has_auto_merge == 'true'
        uses: actions/github-script@v7
        with:
          script: |
            await github.rest.issues.addLabels({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.payload.pull_request.number,
              labels: ["auto-merge"]
            });