name: Docker Build & Publish

# This tells GitHub: "Run this every time I push code to the main branch"
on:
  push:
    branches: [ "main" ]
    # Also run if I create a Release tag (e.g., v1.0)
    tags: [ 'v*.*.*' ]
  pull_request:
    branches: [ "main" ]

env:
  # Use GitHub's built-in registry (ghcr.io)
  REGISTRY: ghcr.io
  # Use the repository name as the image name
  IMAGE_NAME: ${{ github.repository }}

jobs:
  build:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      packages: write # Needed to push the image to GHCR

    steps:
      - name: Checkout repository
        uses: actions/checkout@v3

      # Set up Docker Buildx (The builder engine)
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      # Login to GitHub Container Registry using the automatic GitHub Token
      - name: Log into registry ${{ env.REGISTRY }}
        if: github.event_name != 'pull_request'
        uses: docker/login-action@v2
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      # Generate tags (e.g., :latest, :v1.0, :main)
      - name: Extract Docker metadata
        id: meta
        uses: docker/metadata-action@v4
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          tags: |
            type=raw,value=latest,enable={{is_default_branch}}
            type=ref,event=branch
            type=semver,pattern={{version}}

      # Build the image and push it to the registry
      - name: Build and push Docker image
        uses: docker/build-push-action@v4
        with:
          context: .
          push: ${{ github.event_name != 'pull_request' }}
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}