docker-image.yml

name: Publish Docker Image

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]
  workflow_dispatch:
env:
  # Last fragment of identifier of the docker image
  IMAGE_NAME: ${{ github.repository }}
  # Group identifier of the docker image, typically ${{ github.repository_owner }} or ${{ github.repository }}
  IMAGE_GROUP_NAME: ${{ github.repository_owner }}
  MAIN_BRANCH_NAME: main

jobs:
  build-and-publish:

    runs-on: ubuntu-latest

    steps:
      - name: Exit if pull request is from a fork
        run: |
          if [ "${{ github.event_name }}" == "pull_request" ] && [ "${{ github.event.pull_request.head.repo.name }}" != "${{ github.event.repository.name }}" ]; then
            echo "Skiping workflow as this pull request is from a fork."
            exit 78
          fi
      - uses: actions/checkout@v2

      - name: Build docker image
        run: docker build . --file Dockerfile --tag $IMAGE_NAME

      - name: Log in to the Container registry
        run: echo "${{ github.token }}" | docker login docker.pkg.github.com -u ${{ github.actor }} --password-stdin

      - name: Push image
        run: |
          IMAGE_ID=docker.pkg.github.com/$IMAGE_GROUP_NAME/$IMAGE_NAME
          # Change all uppercase to lowercase
          IMAGE_ID=$(echo $IMAGE_ID | tr '[A-Z]' '[a-z]')
          # Get branch name if merge to a branch
          GIT_BRANCH_NAME=$(echo "${{ github.ref }}" | grep 'refs/heads/.*' | cut -d"/" -f 3)
          # Get pull request id (e.g. "pr-123" from "/pulls/123")
          PULL_REQUEST_ID=$(echo "${{ github.event.pull_request.number }}" | grep -v "^$" | sed 's/^/pr-/')
          # Get tag id while strip "v" prefix (e.g. "1.2" from "v1.2")
          TAG_ID=$(echo "${{ github.ref }}" | grep 'refs/tags/.*' | cut -d"/" -f 3 | sed -e 's/^v//')
          # Version is either "git branch name"/"pull request id"/"tag id"                    
          VERSION=${GIT_BRANCH_NAME:-${PULL_REQUEST_ID:-${TAG_ID}}}
          # Use Docker `latest` tag convention
          [ "$VERSION" == $MAIN_BRANCH_NAME ] && VERSION=latest
          echo IMAGE_ID=$IMAGE_ID
          echo VERSION=$VERSION
          docker tag $IMAGE_NAME $IMAGE_ID:$VERSION
          docker push $IMAGE_ID:$VERSION