Adjust workflow

* Trigger build for PR, but only when from the same repo
* Multi-arch build
* Uses "docker/metadata" action to set up labels and tags

Author: edoardob90

.github/workflows/docker-build.yml

@@ -10,27 +10,59 @@ on:
       - slides/**
       - images/**
       - .gitignore
+  pull_request:
+    paths-ignore:
+      - "*.md"
+      - slides/**
+      - images/**
+      - .gitignore
   workflow_dispatch:
 
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
     permissions:
       packages: write
+    strategy:
+      matrix:
+        arch: [amd64, arm64]
+      fail-fast: false
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
       - name: Setup Docker Buildx
         uses: docker/setup-buildx-action@v3
 
       - name: Log in to GHCR
+        if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
         uses: docker/login-action@v3
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' && matrix.arch == 'amd64' }}
+            type=ref,event=branch
+            type=ref,event=pr
+            type=sha,format=short
+          flavor: |
+            suffix=-${{ matrix.arch }}
+
       - name: Build and push
         uses: docker/build-push-action@v6
         with:
-          platforms: linux/amd64,linux/arm64
-          push: true
-          tags: ghcr.io/${{ github.repository }}:latest
+          context: .
+          platforms: linux/${{ matrix.arch }}
+          push: ${{ github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}