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.github/workflows/docker-publish.yml

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+# .github/workflows/docker-publish.yml
+
+name: Docker Image CI for Electricity Calculator
+
+# Controls when the workflow will run
+on:
+  push:
+    branches: [ "main" ] # Triggers on pushes to the main branch
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+jobs:
+  build_and_push_to_ghcr:
+    name: Build and Push to GitHub Container Registry
+    runs-on: ubuntu-latest # Use the latest Ubuntu runner
+
+    permissions:
+      contents: read      # Needed to checkout the repository
+      packages: write     # Needed to push to GitHub Packages (GHCR)
+      # id-token: write    # Uncomment if using OIDC for authentication with a cloud provider
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        # This step checks out your repository under $GITHUB_WORKSPACE, so your workflow can access it.
+
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }} # Your GitHub username or organization name
+          password: ${{ secrets.GITHUB_TOKEN }}
+        # This step logs in to GHCR using a GITHUB_TOKEN, which is automatically generated for each job run.
+        # The GITHUB_TOKEN has permissions to push to GHCR if 'packages: write' is set for the job.
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository_owner }}/electricity-calculator-app
+          # Generates tags:
+          # - 'latest' for the default branch
+          # - Git tag if a tag is pushed
+          # - Git SHA as a tag
+          tags: |
+            type=schedule
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+            type=sha
+            latest
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: . # Build context is the root of the repository (where Dockerfile is)
+          file: ./Dockerfile # Explicitly specify the Dockerfile name if it's not 'Dockerfile' or is in a subdirectory
+          push: true # Actually push the image after building
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+        # This step builds the Docker image using the Dockerfile in your repository
+        # and pushes it to GHCR with the tags generated in the previous step.
+
+      - name: Image digest
+        run: echo ${{ steps.build_and_push.outputs.digest }}
+        # Optional: Outputs the digest of the pushed image.