name: Enforce PR Origin Policy

on:
  pull_request:
    types: [ opened, reopened, synchronize ]

jobs:
  validate-pr-origin:
    runs-on: ubuntu-latest
    env:
      PR_NUMBER: ${{ github.event.pull_request.number }}
      SOURCE_REPO: ${{ github.event.pull_request.head.repo.full_name }}
      SOURCE_BRANCH: ${{ github.event.pull_request.head.ref }}
      TARGET_REPO: ${{ github.repository }}
      TARGET_BRANCH: ${{ github.event.pull_request.base.ref }}

    steps:
      - name: Print PR source info
        run: |
          echo "PR source information:"
          echo "  - PR Number: $PR_NUMBER"
          echo "  - Source repo: $SOURCE_REPO"
          echo "  - Source branch: $SOURCE_BRANCH"
          echo "  - Target repo: $TARGET_REPO"
          echo "  - Target branch: $TARGET_BRANCH"

      - name: Validate PR origin and target branch
        run: |
          # PRs must come from a fork
          if [ "$SOURCE_REPO" = "$TARGET_REPO" ]; then
            echo "❌ PR must come from a fork."
            exit 1
          fi

          # PRs cannot come from the 'main' branch of a fork
          if [ "$SOURCE_BRANCH" = "main" ]; then
            echo "❌ PR cannot come from the 'main' branch of a fork."
            exit 1
          fi

          echo "✅ PR passed origin and target branch checks."