arbys/default.nix

{
  pkgs,
  lib,
  config,
  ...
}:
let
  inherit (lib)
    mkEnableOption
    mkOption
    mkIf
    ;
  inherit (lib.types)
    submodule
    bool
    nullOr
    lines
    str
    path
    int
    attrsOf
    either
    ;
  fileType = submodule (
    { options, ... }:
    {
      options = {
        enable = mkEnableOption "creation of this file" // {
          default = true;
          example = false;
        };

        text = mkOption {
          default = "";
          type = lines;
          description = "Text of the file";
        };

        source = mkOption {
          type = nullOr (either path str);
          default = null;
          description = "Path of the source file or directory - be sure to quote paths you don't want nix to copy to the store.";
        };

        executable = mkOption {
          type = bool;
          default = false;
          example = true;
          description = ''
            Whether to set the execute bit on the target file.
            Only effective in combination with `.text` specified, else permissions will be of the source file.
          '';
        };

        uid = mkOption {
          type = nullOr int;
          default = null;
          description = ''
            Uid this file will belong to
          '';
        };

        gid = mkOption {
          type = nullOr int;
          default = null;
          description = ''
            Gid this file will belong to
          '';
        };

        clobber = mkOption {
          default = config.environment.arbys.clobber;
          defaultText = ''config.environment.arbys.clobber'';
          type = bool;
          description = ''
            Whether to clobber file or throw error on conflict
          '';
        };

      };
    }
  );
in
{
  options.environment = {
    arbys = {
      clobber = mkOption {
        type = bool;
        default = false;
        description = ''
          Whether to clobber conflicted files by default
        '';
      };
      enable = mkEnableOption "Arbitrary Symlink Manager";
    };
    files = mkOption {
      description = "Files to link";
      type = attrsOf fileType;
      default = { };
    };
  };
  config =
    let
      files =
        let
          enabled = lib.filterAttrs (_: v: v.enable) config.environment.files;
          sourced = builtins.mapAttrs (
            n: v:
            let
              processed =
                if (v.source == null) then
                  (
                    if (v.text == "") then
                      throw "Must provide source or text for ${n}"
                    else
                      v
                      // {
                        source = pkgs.writeTextFile {
                          name = "${n}-source";
                          text = v.text;
                          executable = v.executable ? false;
                        };
                      }
                  )
                else
                  v;
              filtered = builtins.removeAttrs processed [
                "text"
                "enable"
                "executable"
              ];
              nullFiltered = lib.filterAttrs (_: v: v != null) filtered;
            in
            nullFiltered
            // {
              type = "symlink";
            }
          ) enabled;
        in
        lib.foldlAttrs (
          acc: n: v:
          acc ++ (lib.singleton ({ target = n; } // v))
        ) [ ] sourced;
      manifest = pkgs.writeTextFile {
        name = "manifest.json";
        text = (
          builtins.toJSON {
            inherit files;
            clobber_by_default = config.environment.arbys.clobber;
            version = 1;
          }
        );
        checkPhase = ''
          set -e
          CUE_CACHE_DIR=$(pwd)/.cache
          CUE_CONFIG_DIR=$(pwd)/.config

          ${lib.getExe pkgs.cue} vet -c ${./v1.cue} $target
        '';
      };
    in
    mkIf (config.environment.arbys.enable) {
      systemd.targets.arbys = {
        description = "Create Arbitrary Symlinks";
        after = [ "local-fs.target" ];
        wantedBy = [
          "sysinit-reactivation.target"
          "multi-user.target"
        ];
        before = [ "sysinit-reactivation.target" ];
        requires = [
          "arbys-activate.service"
          "arbys-copy.service"
          "arbys-cleanup.service"
        ];
      };

      systemd.services =
        let
          manifestPath = "/var/lib/arbys";
        in
        {
          arbys-prep = {
            description = "Ensure manifest dir exists";
            script = "mkdir -p ${manifestPath}";
            serviceConfig.Type = "oneshot";
            unitConfig.RefuseManualStart = true;
          };

          arbys-activate = {
            description = "Link files from arbys manifest";
            serviceConfig.Type = "oneshot";
            requires = [
              "arbys-prep.service"
              "arbys-copy.service"
            ];
            after = [ "arbys-prep.service" ];
            script =
              let
                linker = lib.getExe (pkgs.smfh or (pkgs.rustPlatform.buildRustPackage ./smfh.nix { }));
              in
              ''
                new_manifest=${manifest}

                if [ ! -f ${manifestPath}/manifest.json ]; then
                  ${linker} activate $new_manifest
                  exit 0
                fi;

                ${linker} diff $new_manifest ${manifestPath}/manifest.json
              '';
          };

          arbys-copy = {
            description = "Copy manifest into the state dir";
            serviceConfig.Type = "oneshot";
            after = [ "arbys-activate.service" ];
            script = "cp ${manifest} ${manifestPath}/manifest.json";
          };

          arbys-cleanup = {
            description = "Clean up manifest if disabled";
            serviceConfig.type = "oneshot";
            after = [ "arbys.target" ];
            unitConfig.RefuseManualStart = false;
            script =
              if (lib.count (builtins.attrNames config.environment.files) == 0) then
                "rm ${manifestPath}/manifest.json"
              else
                "true";
          };
        };
    };
}