name: 🔁 Weekly Branch Promotions

on:
  schedule:
    - cron: "0 6 * * 1"
  workflow_dispatch:

permissions:
  contents: read
  pull-requests: write

concurrency:
  group: weekly-branch-promotions
  cancel-in-progress: false

jobs:
  open-promotion-pr:
    name: Open ${{ matrix.head }} → ${{ matrix.base }}
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        include:
          - head: develop
            base: design
            title: "chore: merge develop into design"
          - head: design
            base: main
            title: "chore: merge design into main"

    steps:
      - name: ⬇️ Checkout
        uses: actions/checkout@v6
        with:
          fetch-depth: 0

      - name: 🔁 Open promotion PR
        env:
          GH_TOKEN: ${{ github.token }}
          BASE_BRANCH: ${{ matrix.base }}
          HEAD_BRANCH: ${{ matrix.head }}
          PR_TITLE: ${{ matrix.title }}
        run: |
          set -euo pipefail

          git fetch origin "$BASE_BRANCH" "$HEAD_BRANCH"

          if git merge-base --is-ancestor "origin/$HEAD_BRANCH" "origin/$BASE_BRANCH"; then
            echo "No promotion needed: $BASE_BRANCH already contains $HEAD_BRANCH."
            exit 0
          fi

          existing_pr="$(gh pr list \
            --state open \
            --base "$BASE_BRANCH" \
            --head "$GITHUB_REPOSITORY_OWNER:$HEAD_BRANCH" \
            --json number \
            --jq '.[0].number // empty')"

          if [ -n "$existing_pr" ]; then
            echo "Promotion PR already open: #$existing_pr."
            exit 0
          fi

          gh pr create \
            --base "$BASE_BRANCH" \
            --head "$HEAD_BRANCH" \
            --title "$PR_TITLE" \
            --body "Automated weekly promotion PR from \`$HEAD_BRANCH\` to \`$BASE_BRANCH\`."