name: Auto Backport

on:
  pull_request_target:
    types: [closed]
    branches: [main]

jobs:
  backport:
    if: github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'needs-backport')
    runs-on: ubuntu-latest
    permissions:
      contents: write
      pull-requests: write
      issues: write

    steps:
      - name: Checkout repository
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Configure git
        run: |
          git config user.name "github-actions[bot]"
          git config user.email "github-actions[bot]@users.noreply.github.com"

      - name: Extract version labels
        id: versions
        run: |
          # Extract version labels (e.g., "1.24", "1.22")
          VERSIONS=""
          LABELS='${{ toJSON(github.event.pull_request.labels) }}'
          for label in $(echo "$LABELS" | jq -r '.[].name'); do
            # Match version labels like "1.24" (major.minor only)
            if [[ "$label" =~ ^[0-9]+\.[0-9]+$ ]]; then
              # Validate the branch exists before adding to list
              if git ls-remote --exit-code origin "core/${label}" >/dev/null 2>&1; then
                VERSIONS="${VERSIONS}${label} "
              else
                echo "::warning::Label '${label}' found but branch 'core/${label}' does not exist"
              fi
            fi
          done

          if [ -z "$VERSIONS" ]; then
            echo "::error::No version labels found (e.g., 1.24, 1.22)"
            exit 1
          fi

          echo "versions=${VERSIONS}" >> $GITHUB_OUTPUT
          echo "Found version labels: ${VERSIONS}"

      - name: Backport commits
        id: backport
        env:
          PR_NUMBER: ${{ github.event.pull_request.number }}
          PR_TITLE: ${{ github.event.pull_request.title }}
          MERGE_COMMIT: ${{ github.event.pull_request.merge_commit_sha }}
        run: |
          FAILED=""
          SUCCESS=""

          for version in ${{ steps.versions.outputs.versions }}; do
            echo "::group::Backporting to core/${version}"

            TARGET_BRANCH="core/${version}"
            BACKPORT_BRANCH="backport-${PR_NUMBER}-to-${version}"

            # Fetch target branch (fail if doesn't exist)
            if ! git fetch origin "${TARGET_BRANCH}"; then
              echo "::error::Target branch ${TARGET_BRANCH} does not exist"
              FAILED="${FAILED}${version}:branch-missing "
              echo "::endgroup::"
              continue
            fi

            # Create backport branch
            git checkout -b "${BACKPORT_BRANCH}" "origin/${TARGET_BRANCH}"

            # Try cherry-pick
            if git cherry-pick "${MERGE_COMMIT}"; then
              git push origin "${BACKPORT_BRANCH}"
              SUCCESS="${SUCCESS}${version}:${BACKPORT_BRANCH} "
              echo "Successfully created backport branch: ${BACKPORT_BRANCH}"
              # Return to main (keep the branch, we need it for PR)
              git checkout main
            else
              # Get conflict info
              CONFLICTS=$(git diff --name-only --diff-filter=U | tr '\n' ',')
              git cherry-pick --abort

              echo "::error::Cherry-pick failed due to conflicts"
              FAILED="${FAILED}${version}:conflicts:${CONFLICTS} "

              # Clean up the failed branch
              git checkout main
              git branch -D "${BACKPORT_BRANCH}"
            fi

            echo "::endgroup::"
          done

          echo "success=${SUCCESS}" >> $GITHUB_OUTPUT
          echo "failed=${FAILED}" >> $GITHUB_OUTPUT

          if [ -n "${FAILED}" ]; then
            exit 1
          fi

      - name: Create PR for each successful backport
        if: steps.backport.outputs.success
        env:
          GH_TOKEN: ${{ secrets.PR_GH_TOKEN }}
        run: |
          PR_TITLE="${{ github.event.pull_request.title }}"
          PR_NUMBER="${{ github.event.pull_request.number }}"
          PR_AUTHOR="${{ github.event.pull_request.user.login }}"

          for backport in ${{ steps.backport.outputs.success }}; do
            IFS=':' read -r version branch <<< "${backport}"

            if PR_URL=$(gh pr create \
              --base "core/${version}" \
              --head "${branch}" \
              --title "[backport ${version}] ${PR_TITLE}" \
              --body "Backport of #${PR_NUMBER} to \`core/${version}\`"$'\n\n'"Automatically created by backport workflow." \
              --label "backport" 2>&1); then

              # Extract PR number from URL
              PR_NUM=$(echo "${PR_URL}" | grep -o '[0-9]*$')

              if [ -n "${PR_NUM}" ]; then
                gh pr comment "${PR_NUMBER}" --body "@${PR_AUTHOR} Successfully backported to #${PR_NUM}"
              fi
            else
              echo "::error::Failed to create PR for ${version}: ${PR_URL}"
              # Still try to comment on the original PR about the failure
              gh pr comment "${PR_NUMBER}" --body "@${PR_AUTHOR} Backport branch created but PR creation failed for \`core/${version}\`. Please create the PR manually from branch \`${branch}\`"
            fi
          done

      - name: Comment on failures
        if: failure() && steps.backport.outputs.failed
        env:
          GH_TOKEN: ${{ github.token }}
        run: |
          PR_NUMBER="${{ github.event.pull_request.number }}"
          PR_AUTHOR="${{ github.event.pull_request.user.login }}"
          MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"

          for failure in ${{ steps.backport.outputs.failed }}; do
            IFS=':' read -r version reason conflicts <<< "${failure}"

            if [ "${reason}" = "branch-missing" ]; then
              gh pr comment "${PR_NUMBER}" --body "@${PR_AUTHOR} Backport failed: Branch \`core/${version}\` does not exist"

            elif [ "${reason}" = "conflicts" ]; then
              # Convert comma-separated conflicts back to newlines for display
              CONFLICTS_LIST=$(echo "${conflicts}" | tr ',' '\n' | sed 's/^/- /')

              COMMENT_BODY="@${PR_AUTHOR} Backport to \`core/${version}\` failed: Merge conflicts detected."$'\n\n'"Please manually cherry-pick commit \`${MERGE_COMMIT}\` to the \`core/${version}\` branch."$'\n\n'"<details><summary>Conflicting files</summary>"$'\n\n'"${CONFLICTS_LIST}"$'\n\n'"</details>"
              gh pr comment "${PR_NUMBER}" --body "${COMMENT_BODY}"
            fi
          done