name: Build Docker image

on:
  push:

  # Run on pull requests to verify that the image still builds correctly
  # The image is not pushed on pull requests
  pull_request:
    paths:
      - Dockerfile
      - .github/workflows/image.yml

permissions:
  packages: write

env:
  REGISTRY_IMAGE: ghcr.io/gohugoio/hugo

jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        platform:
          - linux/amd64
          - linux/arm64
    steps:
      - name: Prepare
        run: |
          platform=${{ matrix.platform }}
          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV

      - name: Checkout
        uses: actions/checkout@v4.1.6

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v5.5.1
        with:
          images: ${{ env.REGISTRY_IMAGE }}

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3.0.0

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3.3.0

      - name: Login to GHCR
        # Login is only needed when the image is pushed
        if: ${{ startsWith(github.ref, 'refs/tags') }}
        uses: docker/login-action@v3.2.0
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Build and push by digest
        id: build
        uses: docker/build-push-action@v5.3.0
        with:
          context: .
          push: ${{ startsWith(github.ref, 'refs/tags') }}
          platforms: ${{ matrix.platform }}
          labels: ${{ steps.meta.outputs.labels }}
          outputs: type=image,name=${{ env.REGISTRY_IMAGE }},push-by-digest=true,name-canonical=true,push=true

      - name: Export digest
        run: |
          mkdir -p /tmp/digests
          digest="${{ steps.build.outputs.digest }}"
          touch "/tmp/digests/${digest#sha256:}"

      - name: Upload digest
        uses: actions/upload-artifact@v4.3.3
        with:
          name: digests-${{ env.PLATFORM_PAIR }}
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    runs-on: ubuntu-latest
    needs:
      - build
    if: ${{ startsWith(github.ref, 'refs/tags') }}
    steps:
      - name: Download digests
        uses: actions/download-artifact@v4.1.7
        with:
          path: /tmp/digests
          pattern: digests-*
          merge-multiple: true

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3.3.0

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v5.5.1
        with:
          images: ${{ env.REGISTRY_IMAGE }}

          flavor: |
            latest=false

          # Tag the image with the v-prefixed semver version on tags, tag with the ref on PRs
          tags: |
            type=semver,pattern={{raw}}
            type=ref,event=pr

      - name: Login to GHCR
        uses: docker/login-action@v3.2.0
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Create manifest list and push
        working-directory: /tmp/digests
        run: |
          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
            $(printf '${{ env.REGISTRY_IMAGE }}@sha256:%s ' *)

      - name: Inspect image
        run: |
          docker buildx imagetools inspect ${{ env.REGISTRY_IMAGE }}:${{ steps.meta.outputs.version }}