name: Automatic Backport

on:
  pull_request_target:
    types: [closed, labeled]   # fires when PR is closed (merged) or labeled

concurrency:
  group: backport-${{ github.workflow }}-${{ github.event.pull_request.number }}
  cancel-in-progress: true

permissions:
  contents: write
  pull-requests: write

jobs:
  # Determine which backports are needed
  prepare:
    if: |
      github.event.pull_request.merged == true &&
      (
        contains(github.event.pull_request.labels.*.name, 'backport') ||
        contains(github.event.pull_request.labels.*.name, 'backport-previous') ||
        (github.event.action == 'labeled' && (github.event.label.name == 'backport' || github.event.label.name == 'backport-previous'))
      )
    runs-on: [self-hosted]
    outputs:
      backport_current: ${{ steps.labels.outputs.backport }}
      backport_previous: ${{ steps.labels.outputs.backport_previous }}
      current_branch: ${{ steps.branches.outputs.current_branch }}
      previous_branch: ${{ steps.branches.outputs.previous_branch }}
    steps:
      - name: Check which labels are present
        id: labels
        uses: actions/github-script@v7
        with:
          script: |
            const pr = context.payload.pull_request;
            const labels = pr.labels.map(l => l.name);
            const isBackport = labels.includes('backport');
            const isBackportPrevious = labels.includes('backport-previous');
            
            core.setOutput('backport', isBackport ? 'true' : 'false');
            core.setOutput('backport_previous', isBackportPrevious ? 'true' : 'false');
            
            console.log(`backport label: ${isBackport}, backport-previous label: ${isBackportPrevious}`);
      
      - name: Determine target branches
        id: branches
        uses: actions/github-script@v7
        with:
          script: |
            // Get latest release
            let latestRelease;
            try {
              latestRelease = await github.rest.repos.getLatestRelease({
                owner: context.repo.owner,
                repo: context.repo.repo
              });
            } catch (e) {
              core.setFailed('No existing releases found; cannot determine backport target.');
              return;
            }
            
            const [maj, min] = latestRelease.data.tag_name.replace(/^v/, '').split('.');
            const currentBranch = `release-${maj}.${min}`;
            const prevMin = parseInt(min) - 1;
            const previousBranch = prevMin >= 0 ? `release-${maj}.${prevMin}` : '';
            
            core.setOutput('current_branch', currentBranch);
            core.setOutput('previous_branch', previousBranch);
            
            console.log(`Current branch: ${currentBranch}, Previous branch: ${previousBranch || 'N/A'}`);
            
            // Verify previous branch exists if we need it
            if (previousBranch && '${{ steps.labels.outputs.backport_previous }}' === 'true') {
              try {
                await github.rest.repos.getBranch({
                  owner: context.repo.owner,
                  repo: context.repo.repo,
                  branch: previousBranch
                });
                console.log(`Previous branch ${previousBranch} exists`);
              } catch (e) {
                core.setFailed(`Previous branch ${previousBranch} does not exist.`);
                return;
              }
            }

  backport:
    needs: prepare
    if: |
      github.event.pull_request.merged == true &&
      (needs.prepare.outputs.backport_current == 'true' || needs.prepare.outputs.backport_previous == 'true')
    runs-on: [self-hosted]
    strategy:
      matrix:
        backport_type: [current, previous]
    steps:
      # 1. Determine target branch based on matrix
      - name: Set target branch
        id: target
        if: |
          (matrix.backport_type == 'current' && needs.prepare.outputs.backport_current == 'true') ||
          (matrix.backport_type == 'previous' && needs.prepare.outputs.backport_previous == 'true')
        run: |
          if [ "${{ matrix.backport_type }}" == "current" ]; then
            echo "branch=${{ needs.prepare.outputs.current_branch }}" >> $GITHUB_OUTPUT
            echo "Target branch: ${{ needs.prepare.outputs.current_branch }}"
          else
            echo "branch=${{ needs.prepare.outputs.previous_branch }}" >> $GITHUB_OUTPUT
            echo "Target branch: ${{ needs.prepare.outputs.previous_branch }}"
          fi
      
      # 2. Checkout (required by backport‑action)
      - name: Checkout repository
        if: steps.target.outcome == 'success'
        uses: actions/checkout@v4

      # 3. Create the back‑port pull request
      - name: Create back‑port PR
        id: backport
        if: steps.target.outcome == 'success'
        uses: korthout/backport-action@v3.2.1
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          label_pattern: '' # don't read labels for targets
          target_branches: ${{ steps.target.outputs.branch }}
          merge_commits: skip
          conflict_resolution: draft_commit_conflicts