name: Publish image

# Build and push the Docker image to the GitHub Container Registry
# (ghcr.io) on version tags only.
on:
  push:
    tags:
      - 'v*'

env:
  REGISTRY: ghcr.io
  IMAGE_NAME: ${{ github.repository }}

jobs:
  publish:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      packages: write
    steps:
      - name: Checkout
        uses: actions/checkout@v4

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Log in to GitHub Container Registry
        uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Extract image metadata
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          # v1.2.3 -> 1.2.3, 1.2, 1 ; plus a moving `latest` for the newest tag.
          tags: |
            type=semver,pattern={{version}}
            # A fix to release 1.2.3 is tagged v1.2.3.1: four numbers are not semver, so
            # the pattern above makes no tag for it; this one does (image tag 1.2.3.1).
            type=match,pattern=v(\d+\.\d+\.\d+\.\d+),group=1
            type=semver,pattern={{major}}.{{minor}}
            type=semver,pattern={{major}}
            type=raw,value=latest

      - name: Build and push
        uses: docker/build-push-action@v6
        with:
          context: .
          file: ./Dockerfile
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          cache-from: type=gha
          cache-to: type=gha,mode=max