tag-alias.yaml

name: Tag Alias

# Retags an existing image in GHCR under a custom name, without rebuilding.
# Uses `docker buildx imagetools create` so the multi-arch manifest is preserved.
# Re-running with the same name updates the alias to point at a different source tag.
on:
  workflow_dispatch:
    inputs:
      name:
        description: "Alias name (e.g., potato)"
        required: true
      source_tag:
        description: "Source tag to alias from"
        required: false
        default: "latest"

env:
  REGISTRY: ghcr.io
  IMAGE_NAME: ${{ github.repository }}

jobs:
  alias:
    runs-on: ubuntu-latest

    permissions:
      contents: read
      packages: write

    steps:
      - name: Validate alias name
        env:
          NAME: ${{ inputs.name }}
        run: |
          if ! [[ "$NAME" =~ ^[A-Za-z0-9_][A-Za-z0-9_.-]{0,127}$ ]]; then
            echo "Invalid alias name '$NAME' (allowed: [A-Za-z0-9_.-], must start with [A-Za-z0-9_], max 128 chars)."
            exit 1
          fi
          if [[ "$NAME" == "latest" || "$NAME" == "main" ]]; then
            echo "Alias name '$NAME' is reserved by the build workflow."
            exit 1
          fi
          if [[ "$NAME" =~ ^[0-9]{2}\.[0-9]{2}(\.[0-9]+)?$ ]]; then
            echo "Alias name '$NAME' looks like a calver tag — pick a non-version name."
            exit 1
          fi

      - name: Log in to GitHub Package Container registry
        uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Create alias tag
        env:
          IMAGE: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          NAME: ${{ inputs.name }}
          SOURCE_TAG: ${{ inputs.source_tag }}
        run: |
          SRC="${IMAGE}:${SOURCE_TAG}"
          DST="${IMAGE}:${NAME}"
          echo "Aliasing $DST -> $SRC"
          docker buildx imagetools create -t "$DST" "$SRC"
          {
            echo "### 🏷️ Tag Alias"
            echo ""
            echo "- Source: \`$SRC\`"
            echo "- Alias:  \`$DST\`"
          } >> "$GITHUB_STEP_SUMMARY"