name: Auto Backport

on:
  pull_request_target:
    types: [closed, labeled]
    branches: [main]
  workflow_dispatch:
    inputs:
      pr_number:
        description: 'PR number to backport'
        required: true
        type: string
      force_rerun:
        description: 'Force rerun even if backports exist'
        required: false
        type: boolean
        default: false

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

    steps:
      - name: Validate inputs for manual triggers
        if: github.event_name == 'workflow_dispatch'
        run: |
          # Validate PR number format
          if ! [[ "${{ inputs.pr_number }}" =~ ^[0-9]+$ ]]; then
            echo "::error::Invalid PR number format. Must be a positive integer."
            exit 1
          fi
          
          # Validate PR exists and is merged
          if ! gh pr view "${{ inputs.pr_number }}" --json merged >/dev/null 2>&1; then
            echo "::error::PR #${{ inputs.pr_number }} not found or inaccessible."
            exit 1
          fi
          
          MERGED=$(gh pr view "${{ inputs.pr_number }}" --json merged --jq '.merged')
          if [ "$MERGED" != "true" ]; then
            echo "::error::PR #${{ inputs.pr_number }} is not merged. Only merged PRs can be backported."
            exit 1
          fi
          
          # Validate PR has needs-backport label
          if ! gh pr view "${{ inputs.pr_number }}" --json labels --jq '.labels[].name' | grep -q "needs-backport"; then
            echo "::error::PR #${{ inputs.pr_number }} does not have 'needs-backport' label."
            exit 1
          fi
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

      - 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: Check if backports already exist
        id: check-existing
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_NUMBER: ${{ github.event_name == 'workflow_dispatch' && inputs.pr_number || github.event.pull_request.number }}
        run: |
          # Check for existing backport PRs for this PR number
          EXISTING_BACKPORTS=$(gh pr list --state all --search "backport-${PR_NUMBER}-to" --json title,headRefName,baseRefName | jq -r '.[].headRefName')
          
          if [ -z "$EXISTING_BACKPORTS" ]; then
            echo "skip=false" >> $GITHUB_OUTPUT
            exit 0
          fi
          
          # For manual triggers with force_rerun, proceed anyway
          if [ "${{ github.event_name }}" = "workflow_dispatch" ] && [ "${{ inputs.force_rerun }}" = "true" ]; then
            echo "skip=false" >> $GITHUB_OUTPUT
            echo "::warning::Force rerun requested - existing backports will be updated"
            exit 0
          fi
          
          echo "Found existing backport PRs:"
          echo "$EXISTING_BACKPORTS"
          echo "skip=true" >> $GITHUB_OUTPUT
          echo "::warning::Backport PRs already exist for PR #${PR_NUMBER}, skipping to avoid duplicates"

      - name: Extract version labels
        if: steps.check-existing.outputs.skip != 'true'
        id: versions
        run: |
          # Extract version labels (e.g., "1.24", "1.22")
          VERSIONS=""
          
          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
            # For manual triggers, get labels from the PR
            LABELS=$(gh pr view ${{ inputs.pr_number }} --json labels | jq -r '.labels[].name')
          else
            # For automatic triggers, extract from PR event
            LABELS='${{ toJSON(github.event.pull_request.labels) }}'
            LABELS=$(echo "$LABELS" | jq -r '.[].name')
          fi
          
          for label in $LABELS; do
            # Match version labels like "1.24" (major.minor only)
            if [[ "$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
        if: steps.check-existing.outputs.skip != 'true'
        id: backport
        env:
          PR_NUMBER: ${{ github.event_name == 'workflow_dispatch' && inputs.pr_number || github.event.pull_request.number }}
        run: |
          FAILED=""
          SUCCESS=""
          
          # Get PR data for manual triggers
          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
            PR_DATA=$(gh pr view ${{ inputs.pr_number }} --json title,mergeCommit)
            PR_TITLE=$(echo "$PR_DATA" | jq -r '.title')
            MERGE_COMMIT=$(echo "$PR_DATA" | jq -r '.mergeCommit.oid')
          else
            PR_TITLE="${{ github.event.pull_request.title }}"
            MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"
          fi

          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.check-existing.outputs.skip != 'true' && steps.backport.outputs.success
        env:
          GH_TOKEN: ${{ secrets.PR_GH_TOKEN }}
          PR_NUMBER: ${{ github.event_name == 'workflow_dispatch' && inputs.pr_number || github.event.pull_request.number }}
        run: |
          # Get PR data for manual triggers
          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
            PR_DATA=$(gh pr view ${{ inputs.pr_number }} --json title,author)
            PR_TITLE=$(echo "$PR_DATA" | jq -r '.title')
            PR_AUTHOR=$(echo "$PR_DATA" | jq -r '.author.login')
          else
            PR_TITLE="${{ github.event.pull_request.title }}"
            PR_AUTHOR="${{ github.event.pull_request.user.login }}"
          fi
          
          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: steps.check-existing.outputs.skip != 'true' && failure() && steps.backport.outputs.failed
        env:
          GH_TOKEN: ${{ github.token }}
        run: |
          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
            PR_DATA=$(gh pr view ${{ inputs.pr_number }} --json author,mergeCommit)
            PR_NUMBER="${{ inputs.pr_number }}"
            PR_AUTHOR=$(echo "$PR_DATA" | jq -r '.author.login')
            MERGE_COMMIT=$(echo "$PR_DATA" | jq -r '.mergeCommit.oid')
          else
            PR_NUMBER="${{ github.event.pull_request.number }}"
            PR_AUTHOR="${{ github.event.pull_request.user.login }}"
            MERGE_COMMIT="${{ github.event.pull_request.merge_commit_sha }}"
          fi

          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