name: Resolve buildx cache settings
description: >-
  Turns the DOCKER_CACHE_* variables exported by the runner into buildx driver options and
  cache refs. Missing variables degrade the job to a build without cache instead of failing it.

inputs:
  cache-image:
    description: Cache image path without the registry host (e.g. "org/repo/app").
    required: true

outputs:
  driver-opts:
    description: driver-opts for docker/setup-buildx-action; empty when the cache registry needs no network pinning.
    value: ${{ steps.resolve.outputs.driver-opts }}
  cache-from:
    description: cache-from ref for docker/build-push-action; empty disables cache reads.
    value: ${{ steps.resolve.outputs.cache-from }}
  cache-to:
    description: cache-to ref for docker/build-push-action; empty disables cache writes.
    value: ${{ steps.resolve.outputs.cache-to }}

runs:
  using: composite
  steps:
    - id: resolve
      shell: bash
      env:
        CACHE_IMAGE: ${{ inputs.cache-image }}
      run: |
        if [ -n "${DOCKER_CACHE_NETWORK}" ]; then
          echo "driver-opts=network=${DOCKER_CACHE_NETWORK}" >> "$GITHUB_OUTPUT"
        else
          echo "driver-opts=" >> "$GITHUB_OUTPUT"
        fi

        if [ -z "${DOCKER_CACHE_TYPE}" ] || [ -z "${DOCKER_CACHE_SERVER}" ]; then
          echo "::warning::DOCKER_CACHE_* not set on the runner - building without cache"
          echo "cache-from=" >> "$GITHUB_OUTPUT"
          echo "cache-to=" >> "$GITHUB_OUTPUT"
          exit 0
        fi

        ref="${DOCKER_CACHE_SERVER}/${CACHE_IMAGE}:cache"
        echo "cache-from=type=${DOCKER_CACHE_TYPE},ref=${ref},registry.insecure=true" >> "$GITHUB_OUTPUT"
        echo "cache-to=type=${DOCKER_CACHE_TYPE},ref=${ref},registry.insecure=true,mode=max" >> "$GITHUB_OUTPUT"