action.yml

---
# https://help.github.com/en/articles/metadata-syntax-for-github-actions
name: 'Docker tag action'
description: "GitHub Action to create Docker tag based on branch or tag"
author: 'cytopia'
branding:
  icon: 'code'
  color: 'red'

inputs:
  latest_git_branch:
    description: 'Git branch name which will return "latest" as the Docker tag (default: master).'
    required: false
    default: 'master'
  latest_docker_tag_name:
    description: 'The name for the "latest" Docker tag (default: latest).'
    required: false
    default: 'latest'
  non_latest_docker_tag_prefix:
    description: 'The prefix for all Docker tags, which do not identify as the conventional latest Tag (default: empty)'
    required: false
    default: ''
  non_latest_docker_tag_suffix:
    description: 'The suffix for all Docker tags, which do not identify as the conventional latest Tag (default: empty)'
    required: false
    default: ''

outputs:
  docker-tag:
    description: "Docker tag to be used"
    value: ${{ steps.get-docker-tag.outputs.docker-tag }}

runs:
  using: "composite"
  steps:
    - name: Get Docker Tag
      id: get-docker-tag
      shell: bash
      run: |
        # Commit, Branch or Tag
        HEAD="$( git branch --no-color | grep '^\*' | sed 's|)||g' | xargs -n1 | tail -1 )"

        # Get current Commit Hash (short)
        HASH="$( git rev-parse --short HEAD )"

        # Hash is found in what Branch?
        FROM="$( git branch --contains "${HASH}" | head -2 | tac | head -1 | sed 's|^*[[:space:]]*||g' | sed 's|)||g' | xargs -n1 | tail -1 | xargs )"

        # How many commits behind FROM branch
        BEHIND="$( git rev-list --count "${HASH}..${FROM}" )"

        ###
        ### TAG
        ###
        if git name-rev "${HEAD}" | grep -E "^${HEAD} tags/${HEAD}" > /dev/null; then
            GIT_NAME="${HEAD}"
            GIT_TYPE="TAG"
            GIT_HEAD="${HASH}"
            DETACHED_FROM=${FROM}"
            BEHIND=${BEHIND}"
        ###
        ### Branch or Detached Commit
        ###
        else
            # Detached Commit (not latest in branch)
            if [ "${BEHIND}" -gt "0" ]; then
                GIT_NAME="${HEAD}"
                GIT_TYPE="COMMIT"
                GIT_HEAD="${HASH}"
                DETACHED_FROM="${FROM}"
                BEHIND="${BEHIND}"
            else
                if [ "$( git branch | grep '^\*' | sed 's|^*[[:space:]]*||g' | xargs )" = "${FROM}" ]; then
                    DETACHED=
                else
                    DETACHED="${FROM}"
                fi
                GIT_NAME="${FROM}"
                GIT_TYPE="BRANCH"
                GIT_HEAD="${HASH}"
                DETACHED_FROM="${DETACHED}"
                BEHIND="${BEHIND}"
            fi
        fi

        ###
        ### Determine Docker tag
        ###
        if [ "${GIT_TYPE}" = "BRANCH" ] && [ "${GIT_NAME}" = "${{ inputs.latest_git_branch }}" ]; then
          DOCKER_TAG="${{ inputs.latest_docker_tag_name }}"
        else
          DOCKER_TAG="${{ inputs.non_latest_docker_tag_prefix }}${GIT_NAME}${{ inputs.non_latest_docker_tag_suffix }}"
        fi

        ###
        ### Replace slashes '/' with dashes '-'
        ###
        DOCKER_TAG="${DOCKER_TAG//\//-}"

        ###
        ### Set final output for 'docker-tag'
        ###
        echo "docker-tag=${DOCKER_TAG}" >> $GITHUB_OUTPUT

        ###
        ### Output information
        ###
        echo "DOCKER_TAG=${DOCKER_TAG}"
        echo "GIT_NAME=${GIT_NAME}"
        echo "GIT_TYPE=${GIT_TYPE}"
        echo "GIT_HEAD=${GIT_HEAD}"
        echo "DETACHED_FROM=${DETACHED_FROM}"
        echo "BEHIND=${BEHIND}"