main.yml

---
name: Determine the Docker 'tags' to use, then invoke the build/test/publish workflow.

on:
  push:
    branches:
      - '*'
    tags:
      - 'v[0-9]+\.[0-9]+\.[0-9]+'
  pull_request:
    branches:
      - '*'
env:
  TAG_PREFIX: prefix # must be lower case

jobs:
  tests:
    uses: "./.github/workflows/test.yml"

  get-tags:
    runs-on: ubuntu-latest
    needs: [tests]
    steps:
      - name: Extract metadata (tags, labels) for Docker
        id: meta
        uses: docker/metadata-action@v4.1.1
        with:
          images: ${{ env.TAG_PREFIX }} # dummy value since blank is not allowed
          tags: |
            type=ref,event=branch
            type=ref,event=pr
            type=semver,pattern={{version}} # major.minor.patch
            type=semver,pattern={{major}}.{{minor}}

      - name: Remove dummy prefix
        id: removed
        run: |
          # comma separated list of tags
          reference_list=${{ steps.meta.outputs.tags }}
          prefix_to_remove=${{ env.TAG_PREFIX }}:
          # remove prefix, e.g., ->"prefix:tag1,prefix:tag2"->"tag1,tag2"
          tags=${reference_list//$prefix_to_remove/}
          echo "tags=$tags" >> $GITHUB_ENV

    outputs:
      tags: ${{ env.tags }}

  docker-build-push:
    if: ${{ github.event_name == 'push' }}
    needs: [get-tags]
    uses: "./.github/workflows/docker_build_push.yml"
    strategy:
      matrix:
        notebook_type:
          - jupyter
          - rstudio

    secrets: inherit
    with:
      TAGS: ${{ needs.get-tags.outputs.tags }}
      NOTEBOOK_TYPE: ${{ matrix.notebook_type }}
...