action.yml

name: 'Pull Docker image'
description: 'Pull Docker image from registry, or load it from cache.'

inputs:
  image:
    description: 'Image name'
    required: true

  cache-directory:
    description: 'Directory to store cache in'
    required: false
    default: '~/.docker-cache'

outputs:
  image:
    description: 'Image name'
    value: ${{ inputs.image }}

runs:
  using: composite
  steps:
    - uses: actions/cache@v4
      id: docker-cache
      with:
        path: ${{ inputs.cache-directory }}
        key: ${{ format('{0}{1}-cache-docker-{2}', runner.os, runner.arch, inputs.image) }}

    - name: 'Generate image name'
      id: hash
      env:
        IMAGE: ${{ inputs.image }}
      shell: bash
      #language=bash
      run: |
        echo "filename=$(echo "$IMAGE" | md5sum | cut -d ' ' -f 1)" >> $GITHUB_OUTPUT

    - name: 'Load cached Docker image'
      if: steps.docker-cache.outputs.cache-hit == 'true'
      env:
        CACHE_DIR: ${{ inputs.cache-directory }}
        FILENAME: ${{ steps.hash.outputs.filename }}
      shell: bash
      #language=bash
      run: |
        docker load -i "$CACHE_DIR/image-$FILENAME.tar"

    - name: 'Pull Docker image'
      if: steps.docker-cache.outputs.cache-hit != 'true'
      env:
        IMAGE: ${{ inputs.image }}
      shell: bash
      #language=bash
      run: |
        # if not present, pull from registry
        EXISTS=$(docker image inspect "$IMAGE" > /dev/null 2>&1 || echo 0)

        if [ $EXISTS -eq 0 ]; then
          echo "Image not found, pulling from registry"
          docker pull "$IMAGE"
        else
          echo "Image found, skipping pull"
        fi

    - name: 'Save image to disk'
      if: steps.docker-cache.outputs.cache-hit != 'true'
      env:
        CACHE_DIR: ${{ inputs.cache-directory }}
        FILENAME: ${{ steps.hash.outputs.filename }}
        IMAGE: ${{ inputs.image }}
      shell: bash
      #language=bash
      run: |
        mkdir -p "$CACHE_DIR"
        docker save -o "$CACHE_DIR/image-$FILENAME.tar" "$IMAGE"