name: Backport merged pull request

# Automates cherry-picking merged PRs onto release branches.
#
# Pre-merge (open PR):
#   An authorized /backport or /cherrypick comment adds one `backport <branch>`
#   label per requested branch. These labels are then picked up automatically
#   when the PR is merged (see the pull_request_target: closed trigger below).
#
# Post-merge (merged PR):
#   - Label a PR with e.g. `backport release-1.17` before merging; the label
#     triggers the backport automatically when the PR closes as merged.
#   - Comment `/backport release-1.17` or `/cherrypick release-1.17` on an
#     already-merged PR to create the backport PR immediately.
#
# In both cases multiple target branches can be space-delimited in a comment:
#   /backport release-1.17 release-1.18
#
# See: https://github.com/velero-io/velero/issues/9603

on:
  pull_request_target:
    types: [closed]
  issue_comment:
    types: [created]

permissions: {}

# Shared condition for authorized /backport or /cherrypick comments.
# Used by both jobs below to avoid duplicating the gate logic.
env:
  AUTHORIZED_COMMENT: >-
    ${{
      github.event_name == 'issue_comment' &&
      github.event.issue.pull_request != '' &&
      github.event.comment.user.id != 97796249 &&
      contains(
        fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'),
        github.event.comment.author_association
      ) &&
      (
        startsWith(github.event.comment.body, '/backport') ||
        startsWith(github.event.comment.body, '/cherrypick')
      )
    }}

jobs:
  # ── Pre-merge: convert a /backport or /cherrypick comment into labels ───────
  # When the PR is still open the backport-action cannot run (it requires a
  # merged commit). Instead, add one `backport <branch>` label per requested
  # branch so that the post-merge job picks them up automatically on close.
  label-for-backport:
    name: Label PR for deferred backport
    # Run only when an authorized command is posted on an *open* (unmerged) PR.
    if: >
      github.repository == 'velero-io/velero' &&
      github.event_name == 'issue_comment' &&
      github.event.issue.pull_request != '' &&
      github.event.issue.state == 'open' &&
      github.event.comment.user.id != 97796249 &&
      contains(
        fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'),
        github.event.comment.author_association
      ) &&
      (
        startsWith(github.event.comment.body, '/backport') ||
        startsWith(github.event.comment.body, '/cherrypick')
      )
    runs-on: ubuntu-latest
    permissions:
      issues: write # apply labels to the PR (PRs share the issues API)
    steps:
      - name: Parse branches and apply labels
        env:
          COMMENT_BODY: ${{ github.event.comment.body }}
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          REPO: ${{ github.repository }}
          PR_NUMBER: ${{ github.event.issue.number }}
        run: |
          # Extract branch names from the first line of the comment.
          # Strip the /backport or /cherrypick prefix; what remains is a
          # space-delimited list of target branch names.
          line=$(printf '%s' "$COMMENT_BODY" | head -n1 | tr -d '\r')
          branches=$(printf '%s' "$line" | sed -E 's#^/(backport|cherrypick)[[:space:]]*##')

          if [ -z "$branches" ]; then
            echo "No target branches specified in comment; nothing to label."
            exit 0
          fi

          for branch in $branches; do
            label="backport ${branch}"
            echo "Applying label: '${label}'"
            # Create the label if it does not exist yet (idempotent).
            gh label create "${label}" --repo "${REPO}" --color "0075ca" \
              --description "Backport to ${branch}" 2>/dev/null || true
            gh issue edit "${PR_NUMBER}" --repo "${REPO}" --add-label "${label}"
          done

  # ── Post-merge: create backport PRs ─────────────────────────────────────────
  backport:
    name: Backport pull request
    # Exclude comments from the backport-action bot (user id 97796249) to prevent
    # recursive triggers. The bot does not post /backport commands, so startsWith
    # already blocks recursion; the id check is defense in depth.
    if: >
      github.repository == 'velero-io/velero' &&
      (
        (
          github.event_name == 'pull_request_target' &&
          github.event.pull_request.merged &&
          contains(toJSON(github.event.pull_request.labels.*.name), '"backport ')
        ) || (
          github.event_name == 'issue_comment' &&
          github.event.issue.pull_request != '' &&
          github.event.issue.state == 'closed' &&
          github.event.comment.user.id != 97796249 &&
          contains(
            fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'),
            github.event.comment.author_association
          ) &&
          (
            startsWith(github.event.comment.body, '/backport') ||
            startsWith(github.event.comment.body, '/cherrypick')
          )
        )
      )
    runs-on: ubuntu-latest
    permissions:
      contents: write # push backport branches and comment
      pull-requests: write # open backport PRs
    steps:
      - name: Parse target branches from comment
        id: parse
        if: github.event_name == 'issue_comment'
        env:
          COMMENT_BODY: ${{ github.event.comment.body }}
        run: |
          # First line only; strip /backport or /cherrypick prefix.
          # Remaining text is a space-delimited list of target branches
          # (may be empty, falls back to labels).
          line=$(printf '%s' "$COMMENT_BODY" | head -n1 | tr -d '\r')
          branches=$(printf '%s' "$line" | sed -E 's#^/(backport|cherrypick)[[:space:]]*##')
          echo "branches=${branches}" >> "$GITHUB_OUTPUT"

      - uses: actions/checkout@v7
        with:
          fetch-depth: 0

      - name: Create backport pull requests
        # Pin to commit SHA: workflow has contents/pull-requests write.
        uses: korthout/backport-action@2e830a1d0b8269505846ddd407a70876913ad1f8 # v4.6.0
        with:
          # Labels like `backport release-1.17` select the target branch.
          label_pattern: '^backport ([^ ]+)$'
          # Prefer draft PRs with conflict markers over failing the job silently.
          experimental: |
            {
              "conflict_resolution": "draft_commit_conflicts"
            }
          # Empty when triggered by merge labels; set when `/backport` or `/cherrypick` includes branches.
          target_branches: ${{ steps.parse.outputs.branches }}
          github_token: ${{ secrets.GITHUB_TOKEN }}