action.yml

name: "Build Docker Image"
description: "Build Docker image for arbitrary revision/branch/tag and push to registry"

inputs:
  tag:
    description: Revision, tag, or branch to build
    required: true
    default: ${{ github.event.repository.default_branch }}
  img_tag:
    description: Tag applied to the container image.
  image:
    description: >-
      Image to build, e.g. ghcr.io/organization/image.
    required: true
  registry:
    description: >-
      Registry that hosts these images; by default, ghcr.io.
    default: ghcr.io
  registry_username:
    description: >-
      Username for logging in to registry. For GHCR (and by default), set to github.actor.
    default: ${{ github.actor }}
  registry_token:
    description: >-
      Token for logging in to registry.  For GHCR (and by default), set to github.token.
    default: ${{ github.token }}
  build-args:
    description: >-
      Arguments to pass to docker build
    required: false
  dockerfile:
    description: >-
      Which file to use to build the image; by default, Dockerfile
    default: Dockerfile
  push_latest:
    description: >-
      Update 'latest' tag when pushing
    default: false
  submodules:
    description: >-
      Whether to checkout submodules (as for actions@v3) and thence build them into the image. Set to false by default as for checkout. If you use submodules, you probably want to set this.
    default: false
  platforms:
    description: >-
      Build images for cross platform support.
    default: "linux/amd64,linux/arm64"
  rebuild:
    description: Rebuild the image manually?
    default: false
  gh_event:
    description: The name of the event that triggered the parent workflow.
outputs:
  ghc_img:
    description: "Export GHCR.io package resource URL"
    value: ${{ steps.ghc_img_id.outputs.ghc_img }}

runs:
  using: composite
  steps:
  - name: Set Inputs & Outputs
    id: set_inputs
    shell: bash
    run: |
      if [ "${{ github.event_name }}" == "workflow_run" ]; then
            echo "ref=${{ github.sha }}" >> $GITHUB_OUTPUT
            echo "push_latest=true" >> $GITHUB_OUTPUT
        else
            # workflow_dispatch or other trigger
            echo "ref=${{ inputs.tag }}" >> $GITHUB_OUTPUT
            echo "push_latest=${{ inputs.push_latest }}" >> $GITHUB_OUTPUT
            echo "img_tag=${{ inputs.img_tag }}" >> $GITHUB_OUTPUT
        fi

  - name: Clone latest repository
    uses: actions/checkout@v4
    with:
      ref: ${{ steps.set_inputs.outputs.ref }}
      submodules: ${{ inputs.submodules }}

  - name: Find commit for tag
    id: tag_check
    uses: hathitrust/github_actions/validate-tag@v1
    with:
      tag: ${{ steps.set_inputs.outputs.ref }}

  - name: Log into container registry
    uses: docker/login-action@v3
    with:
      registry: ${{ inputs.registry }}
      username: ${{ inputs.registry_username }}
      password: ${{ inputs.registry_token }}

  - name: Check if revision exists in container registry
    id: image_check
    shell: bash
    run: |
      echo Checking whether Docker image "$IMAGE":"$TAG" exists
      if docker manifest inspect "$IMAGE":"$TAG" > /dev/null; then
        echo 'image_exists=true' >> $GITHUB_OUTPUT
        echo "image exists!"
      else
        echo "image doesn't exist; Starting to Build and push image"
      fi
    env:
      IMAGE: ${{ inputs.image }}
      TAG: ${{ steps.tag_check.outputs.tag }}

  - name: Check whether to push latest tag
    if: ${{ steps.image_check.outputs.image_exists != 'true' || inputs.rebuild }}
    id: latest_push
    uses: actions/github-script@v7
    env:
      INPUT_PUSH_LATEST: ${{ steps.set_inputs.outputs.push_latest }}
      INPUT_IMAGE: ${{ inputs.image }}
    with:
      script: |
        if ( core.getInput('push_latest') == 'true' ) {
          core.setOutput('latest_tag',core.getInput('image') + ':latest')
        } else {
          core.setOutput('latest_tag',core.getInput('image') + ':unstable')
        }

  - name: Set up QEMU
    if: ${{ steps.image_check.outputs.image_exists != 'true' || inputs.rebuild }}
    # QEMU emulation for the Arm portion of our multi-platform Docker image build. Intel Machines
    uses: docker/setup-qemu-action@v3

  - name: Set up Docker Buildx
    if: ${{ steps.image_check.outputs.image_exists != 'true' || inputs.rebuild }}
    # Required for multi-platform Docker image builds in GitHub Actions that use docker/build-push-action.
    uses: docker/setup-buildx-action@v3

  - name: Build image and push to GHCR
    if: ${{ steps.image_check.outputs.image_exists != 'true' || inputs.rebuild }}
    uses: docker/build-push-action@v5
    with:
      context: .
      push: true
      tags: |
        ${{ inputs.image }}:${{ steps.set_inputs.outputs.img_tag && inputs.img_tag || steps.tag_check.outputs.tag }}
        ${{ inputs.image }}:${{ steps.tag_check.outputs.tag }}
        ${{ steps.latest_push.outputs.latest_tag }}
      file: ${{ inputs.dockerfile }}
      build-args: ${{ inputs.build-args }}
      platforms: ${{ inputs.platforms}}
      cache-from: type=gha
      cache-to: type=gha,mode=max
      provenance: false

  - name: Export GHCR.io resource
    id: ghc_img_id
    shell: bash
    run: echo "ghc_img=${{ inputs.image }}:${{ steps.tag_check.outputs.tag }}" >> $GITHUB_OUTPUT