spec:
  inputs:
    cache_strategy:
      type: string
      description: |
        auto (default) | none | runner | cachix | attic
        Sets the default caching strategy. 
        - "auto": dynamically selects the best strategy for every job based on env variables
        - "none": disables caching
        - "runner", "cachix" & "attic": forces every job to use this strategy

        Can be overridden by setting NIX_CI_CACHE_STRATEGY in the pipeline variables.
      default: "auto"
    cache_files:
      type: array
      description: |
        Files to use as the cache key for the generated pipeline yaml.
        If you use "ci.nix" to define CI, add that here for example.
        Note that max 2 items are allowed in cache:key:files, so use something like
        ["flake.*", "ci.nix"] f. ex. to match flake.lock, flake.nix and ci.nix.
      default: ["flake.nix", "flake.lock"]
    version:
      type: string
      description: |
        Which version of the Nix CI image to use. Using a tag/version is recommended.
    stage_build:
      type: string
      description: The CI stage for building the dynamic pipeline.
      default: build
    stage_trigger:
      type: string
      description: The CI stage for triggering the dynamic pipeline.
      default: trigger
---
stages:
  - $[[ inputs.stage_build ]]
  - $[[ inputs.stage_trigger ]]
variables:
  # These can be overriden, see https://docs.gitlab.com/ci/variables/#cicd-variable-precedence
  # which image should be used by default.
  NIX_CI_IMAGE: registry.gitlab.com/technofab/nix-gitlab-ci/nix-ci:$[[ inputs.version ]]
  # default cache stategy
  NIX_CI_CACHE_STRATEGY: $[[ inputs.cache_strategy ]]
nix-ci:build:
  stage: $[[ inputs.stage_build ]]
  image: $NIX_CI_IMAGE
  cache:
    - key:
        files: $[[ inputs.cache_files ]]
      paths:
        - .nix-ci-pipelines/
    - key: nix
      paths:
        - .nix-cache/
  before_script:
    - |
        # if no explicit pipeline is requested
        if [[ -z "${NIX_CI_PIPELINE_NAME:-}" ]]; then
          # if regex matches, use pipeline "default", otherwise $CI_PIPELINE_SOURCE
          [[ "${CI_PIPELINE_SOURCE}" =~ ${NIX_CI_DEFAULT_SOURCES:-.*} ]] \
            && NIX_CI_PIPELINE_NAME="default" \
            || NIX_CI_PIPELINE_NAME="$CI_PIPELINE_SOURCE";
        fi
        echo "NIX_CI_GENERATED_PIPELINE_NAME=$NIX_CI_PIPELINE_NAME" >> trigger.env
        # inheritance of pipeline variables is a bit weird, so explicitly override them
        # (ctx: setting any of these in the project variables would only apply correctly
        # in this pipeline, not the child pipeline, instead weirdly enough the default 
        # variables above are used). If any other variables are added at the top, add them
        # here aswell
        echo "NIX_CI_IMAGE=$NIX_CI_IMAGE" >> trigger.env
        echo "NIX_CI_CACHE_STRATEGY=$NIX_CI_CACHE_STRATEGY" >> trigger.env

        mkdir -p .nix-ci-pipelines/
        # generated-gitlab-ci.yml exists in the cache
        [[ -f ".nix-ci-pipelines/${NIX_CI_PIPELINE_NAME}.yml" ]] && export CACHED=true && echo "A cached pipeline file exists (skip cache with NIX_CI_FORCE_BUILD)" || true
        # allow the user to manually skip the cache (when the key files are not correctly configured etc.)
        [[ -n "$NIX_CI_FORCE_BUILD" ]] && unset CACHED && echo "Caching skipped for this job (through NIX_CI_FORCE_BUILD)" || true

        # only setup when we need to generate the pipeline yaml
        if [[ -z "$CACHED" ]]; then
          source setup_nix_ci; 
        fi
  script:
    # build the pipeline if it does not exist in the cache
    - >
        if [[ -z "$CACHED" ]]; then 
          nix build .#gitlab-ci:pipeline:${NIX_CI_PIPELINE_NAME} && install result .nix-ci-pipelines/${NIX_CI_PIPELINE_NAME}.yml; 
        fi
  after_script:
    # save to binary cache or Gitlab CI cache only if we actually built something
    #  check if /tmp/nix-store-before exists as $CACHED never exists here and the file only exists if "setup_nix_ci" is called
    - |
        if [[ -f "/tmp/nix-store-before" ]]; then 
          finalize_nix_ci; 
        fi
  artifacts:
    paths:
      - .nix-ci-pipelines/
    reports:
      dotenv: trigger.env

nix-ci:trigger:
  stage: $[[ inputs.stage_trigger ]]
  needs:
    - nix-ci:build
  trigger:
    include:
      - artifact: .nix-ci-pipelines/${NIX_CI_GENERATED_PIPELINE_NAME}.yml
        job: nix-ci:build
    strategy: depend
    forward:
      pipeline_variables: true