add image publishing and CI workflows

.github/workflows/ci.yml

@@ -0,0 +1,26 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    # Confirms the Dockerfile still builds. 
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: false
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

.github/workflows/publish.yml

@@ -0,0 +1,77 @@
+name: Publish image
+
+on:
+  push:
+    tags: ['v*']
+  public:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  packages: write
+
+env:
+  IMAGE: ghcr.io/action-prediction-lab/pepper-box
+
+jobs:
+  publish-tag:
+    # On a tag push to a public repo: build and push that one tag plus :latest.
+    # On a private repo: this job is skipped; the tag still exists in git.
+    if: |
+      github.event_name == 'push' &&
+      github.event.repository.private == false
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: |
+            ${{ env.IMAGE }}:${{ github.ref_name }}
+            ${{ env.IMAGE }}:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+  backfill:
+    # On private->public flip or manual re-run: build every existing v* tag.
+    if: github.event_name == 'public' || github.event_name == 'workflow_dispatch'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push each existing v* tag
+        run: |
+          set -euo pipefail
+          tags=$(git tag --list 'v*' --sort=creatordate)
+          if [[ -z "$tags" ]]; then
+            echo "No v* tags found, nothing to backfill."
+            exit 0
+          fi
+          for tag in $tags; do
+            echo "::group::$tag"
+            git checkout "$tag"
+            docker build -t "$IMAGE:$tag" .
+            docker push "$IMAGE:$tag"
+            echo "::endgroup::"
+          done
+          latest=$(echo "$tags" | tail -1)
+          docker tag "$IMAGE:$latest" "$IMAGE:latest"
+          docker push "$IMAGE:latest"