name: CI

on:
  push:
    branches: [main]
  pull_request:

# A second push to the same branch makes the first run's result irrelevant.
concurrency:
  group: ci-${{ github.ref }}
  cancel-in-progress: true

permissions:
  contents: read

jobs:
  go:
    name: Go
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-go@v5
        with:
          go-version: "1.26"
          cache: true

      - name: Formatting
        run: |
          unformatted=$(gofmt -l .)
          if [ -n "$unformatted" ]; then
            echo "These files are not gofmt'd:"
            echo "$unformatted"
            exit 1
          fi

      - name: Vet
        run: go vet ./...

      # -race is the whole point of running tests in CI for a server with a
      # WebSocket fan-out: a data race is exactly the bug that passes locally.
      - name: Test
        run: go test -race -count=1 ./...

      - name: Build
        run: CGO_ENABLED=0 go build ./...

  docker:
    name: Docker image builds
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: docker/setup-buildx-action@v3

      # Build only — publishing happens on a tag, in release.yml. This job exists
      # so a Dockerfile that no longer builds fails on the pull request rather
      # than at release time.
      - uses: docker/build-push-action@v6
        with:
          context: .
          push: false
          cache-from: type=gha
          cache-to: type=gha,mode=max