name: Backport

on:
  pull_request_target:
    types: [closed]

permissions:
  contents: write
  pull-requests: write

jobs:
  backport:
    name: Backport PR
    if: github.event.pull_request.merged == true
    runs-on: ubuntu-latest
    timeout-minutes: 15
    steps:
      - name: Checkout
        uses: actions/checkout@v6
        with:
          fetch-depth: 0
          token: ${{ secrets.GH_PERSONAL_ACCESS_TOKEN }}

      - name: Extract backport labels
        id: extract-labels
        env:
          LABELS: ${{ toJson(github.event.pull_request.labels.*.name) }}
        run: |
          labels=$(echo "$LABELS" | jq -r '.[]' | grep -oP '^backport-\K.+' || true)
          if [ -z "$labels" ]; then
            echo "No backport labels found, skipping."
            echo "has_labels=false" >> "$GITHUB_OUTPUT"
            exit 0
          fi
          echo "has_labels=true" >> "$GITHUB_OUTPUT"
          echo "targets<<EOF" >> "$GITHUB_OUTPUT"
          echo "$labels" >> "$GITHUB_OUTPUT"
          echo "EOF" >> "$GITHUB_OUTPUT"

      - name: Cherry-pick and create backport PRs
        if: steps.extract-labels.outputs.has_labels == 'true'
        env:
          GH_TOKEN: ${{ secrets.GH_PERSONAL_ACCESS_TOKEN }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          PR_TITLE: ${{ github.event.pull_request.title }}
          PR_BODY: ${{ github.event.pull_request.body }}
          AUTHOR: ${{ github.event.pull_request.merged_by.login }}
          PR_AUTHOR: ${{ github.event.pull_request.user.login }}
          BASE_BRANCH: ${{ github.event.pull_request.base.ref }}
        run: |
          git config user.name "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"

          MERGE_COMMIT=$(gh pr view "$PR_NUMBER" --json mergeCommit --jq '.mergeCommit.oid')

          while IFS= read -r target; do
            release_branch="release/${target}"
            head_branch="backport/${target}/pr-${PR_NUMBER}"

            echo "=== Backporting to ${release_branch} ==="

            if ! git ls-remote --exit-code origin "${release_branch}" >/dev/null 2>&1; then
              echo "WARNING: Branch '${release_branch}' does not exist, skipping."
              continue
            fi

            git fetch origin "${release_branch}"

            git checkout -b "${head_branch}" "origin/${release_branch}"

            if ! git cherry-pick -x "${MERGE_COMMIT}"; then
              echo "ERROR: Cherry-pick failed for ${release_branch}. Aborting and creating an issue instead."
              # Abort and clean up first so the repo is back to a sane state,
              # even if the issue creation below fails.
              git cherry-pick --abort
              git checkout -f "${BASE_BRANCH}"
              git branch -D "${head_branch}"
              gh issue create \
                --title "Backport failure: PR #${PR_NUMBER} to ${release_branch}" \
                --assignee "${PR_AUTHOR}" \
                --body "Cherry-pick of ${MERGE_COMMIT} (PR #${PR_NUMBER}) failed on ${release_branch}. Manual backport required." \
                || true
              continue
            fi

            git push origin "${head_branch}"

            # Ensure the version label (e.g. "v1.2") exists before attaching it.
            # GitHub does not create labels implicitly, so upsert it idempotently.
            gh label create "${target}" \
              --color 0e8a16 \
              --description "Backport to ${release_branch}" \
              --force \
              || true

            gh pr create \
              --base "${release_branch}" \
              --head "${head_branch}" \
              --label "${target}" \
              --title "${PR_TITLE} [Backport ${release_branch}]" \
              --body "Backport of #${PR_NUMBER} to ${release_branch}.

          ---
          Original PR: #${PR_NUMBER}
          Merged by: @${AUTHOR}"

            git checkout "${BASE_BRANCH}"
            git branch -D "${head_branch}"
          done <<< "${{ steps.extract-labels.outputs.targets }}"