name: PR Title Sync

on:
  pull_request:
    types: [opened, synchronize, edited]
    paths:
      - 'VERSION'

concurrency:
  group: pr-title-sync-${{ github.event.pull_request.number }}
  cancel-in-progress: true

jobs:
  sync:
    name: Sync PR title to VERSION
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write
    if: github.actor != 'github-actions[bot]'
    steps:
      - name: Checkout PR head
        uses: actions/checkout@v4
        with:
          fetch-depth: 1
          ref: ${{ github.event.pull_request.head.sha }}

      - name: Read VERSION + current title
        id: inspect
        run: |
          set -euo pipefail
          VERSION=$(cat VERSION | tr -d '[:space:]')
          TITLE=$(jq -r '.pull_request.title' "$GITHUB_EVENT_PATH")
          echo "version=$VERSION" >> "$GITHUB_OUTPUT"
          # Only rewrite titles that ALREADY follow the v<X.Y.Z.W> prefix pattern.
          # Custom titles (no prefix) are left alone — user kept them intentionally.
          if printf '%s' "$TITLE" | grep -qE '^v[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+ '; then
            PREFIX=$(printf '%s' "$TITLE" | awk '{print $1}')
            REST=$(printf '%s' "$TITLE" | sed 's/^v[0-9][0-9.]* //')
            {
              echo "prefix=$PREFIX"
              echo "rest=$REST"
              echo "eligible=true"
            } >> "$GITHUB_OUTPUT"
          else
            echo "eligible=false" >> "$GITHUB_OUTPUT"
          fi

      - name: Rewrite title if version changed
        if: steps.inspect.outputs.eligible == 'true'
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_NUM: ${{ github.event.pull_request.number }}
          NEW_V: ${{ steps.inspect.outputs.version }}
          OLD_PREFIX: ${{ steps.inspect.outputs.prefix }}
          REST: ${{ steps.inspect.outputs.rest }}
        run: |
          if [ "v$NEW_V" = "$OLD_PREFIX" ]; then
            echo "Title already matches v$NEW_V; no change."
            exit 0
          fi
          NEW_TITLE="v$NEW_V $REST"
          echo "Rewriting: $OLD_PREFIX ... → v$NEW_V ..."
          gh pr edit "$PR_NUM" --title "$NEW_TITLE"