{
  system ? builtins.currentSystem,
  inputs ? (import ./.).inputs,
}: let
  pkgs = inputs.nixpkgs.legacyPackages.${system};
  devshell = import inputs.devshell {inherit pkgs system;};

  withCategory = category: attrset: attrset // {inherit category;};
  utils = withCategory "utils";
  docs = withCategory "docs";

  makeDocs = {
    name = "make-docs";
    help = "Execute the docs creating jobs and place the results in ./doc";
    command = ''
      nix build "$PRJ_ROOT#jobs.${pkgs.system}.mkApiReferenceTopLevel" \
        && cp result "$PRJ_ROOT/doc/api-reference.md" \
        && chmod 755 "$PRJ_ROOT//doc/api-reference.md"
      nix build "$PRJ_ROOT#jobs.${pkgs.system}.mkApiReferenceChannels" \
        && cp result "$PRJ_ROOT/doc/api-reference-channels.md" \
        && chmod 755 "$PRJ_ROOT//doc/api-reference-channels.md"
      nix build "$PRJ_ROOT#jobs.${pkgs.system}.mkApiReferenceHome" \
        && cp result "$PRJ_ROOT/doc/api-reference-home.md" \
        && chmod 755 "$PRJ_ROOT//doc/api-reference-home.md"
      nix build "$PRJ_ROOT#jobs.${pkgs.system}.mkApiReferenceDevshell" \
        && cp result "$PRJ_ROOT/doc/api-reference-devshell.md" \
        && chmod 755 "$PRJ_ROOT//doc/api-reference-devshell.md"
      nix build "$PRJ_ROOT#jobs.${pkgs.system}.mkApiReferenceNixos" \
        && cp result "$PRJ_ROOT/doc/api-reference-nixos.md" \
        && chmod 755 "$PRJ_ROOT//doc/api-reference-nixos.md"
    '';
  };

  test = type: name:
    withCategory "tests" {
      name = "check-${name}";
      help = "Checks ${name} ${type}";
      command = ''
        set -e
        # set -x

        diggaurl=
        lockfile_updated=1
        lockfile_present=1
        tempdigga="\"path:$PRJ_ROOT\""

        cleanup() {
          if is $lockfile_present; then
            git checkout -- flake.lock
          elif is $lockfile_updated; then
            git rm -f flake.lock
          fi
          # ensure: restore input
          [ -z $diggaurl ] || ${pkgs.gnused}/bin/sed -i "s|$tempdigga|$diggaurl|g" flake.nix
        }

        digga_fixture() {
          # ensure: replace input
          diggaurl=$({ grep -o '"github:divnix/digga.*"' flake.nix || true; })
          [ -z $diggaurl ] || ${pkgs.gnused}/bin/sed -i "s|$diggaurl|$tempdigga|g" flake.nix
        }

        trap_err() {
          local ret=$?
          cleanup
          echo -e \
            "\033[1m\033[31m""exit $ret: \033[0m\033[1m""command [$BASH_COMMAND] failed""\033[0m"
        }

        is () { [ "$1" -eq "0" ]; }

        trap 'trap_err' ERR

        # --------------------------------------------------------------------------------

        cd $PRJ_ROOT/${type}/${name}

        digga_fixture

        test -f flake.lock && lockfile_present=$? || true
        ${pkgs.nixUnstable}/bin/nix flake lock --update-input digga "$@"; lockfile_updated=$?;
        ${pkgs.nixUnstable}/bin/nix flake show "$@"
        ${pkgs.nixUnstable}/bin/nix flake check "$@"

        cleanup
      '';
    };
in
  devshell.mkShell {
    name = "digga";
    packages = with pkgs; [
      fd
      alejandra
      nixUnstable
    ];

    env = [
      {
        name = "NIX_CONFIG";
        value = ''          extra-experimental-features = nix-command flakes
                  extra-substituters = https://nrdxp.cachix.org https://nix-community.cachix.org
                  extra-trusted-public-keys = nrdxp.cachix.org-1:Fc5PSqY2Jm1TrWfm88l6cvGWwz3s93c6IOifQWnhNW4= nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs='';
      }
    ];

    # tempfix: remove when merged https://github.com/numtide/devshell/pull/123
    devshell.startup.load_profiles = pkgs.lib.mkForce (pkgs.lib.noDepEntry ''
      # PATH is devshell's exorbitant privilige:
      # fence against its pollution
      _PATH=''${PATH}
      # Load installed profiles
      for file in "$DEVSHELL_DIR/etc/profile.d/"*.sh; do
        # If that folder doesn't exist, bash loves to return the whole glob
        [[ -f "$file" ]] && source "$file"
      done
      # Exert exorbitant privilige and leave no trace
      export PATH=''${_PATH}
      unset _PATH
    '');

    commands = [
      (utils {
        command = "git rm --ignore-unmatch -f $PRJ_ROOT/{tests,examples}/*/flake.lock";
        help = "Remove all lock files";
        name = "rm-locks";
      })
      (utils {
        name = "fmt";
        help = "Check Nix formatting";
        command = "alejandra \${@} $PRJ_ROOT";
      })
      (utils {
        name = "evalnix";
        help = "Check Nix parsing";
        command = "fd --extension nix --exec nix-instantiate --parse --quiet {} >/dev/null";
      })

      (test "examples" "devos")
      (test "examples" "groupByConfig")
      (test "examples" "hmOnly")
      (test "examples" "all" // {command = "check-devos && check-groupByConfig && check-hmOnly";})
      (docs {package = pkgs.mdbook;})
      (docs makeDocs)
    ];
  }