outputs: add updater script

outputs.nix

@@ -1,5 +1,6 @@
 {
-  inputs ? import ./inputs.nix {},
+  inputsPath ? ./inputs.nix,
+  inputs ? import inputsPath {},
   selfPath ? ./.
 }:
 
@@ -16,7 +17,7 @@ systems = [
 forEachSystem = lib.genAttrs systems;
 
 self = {
-  inherit inputs lib self;
+  inherit inputs inputsPath lib self;
   outPath = selfPath;
   modifiedNixpkgs     = import ./pkgs/top-level/impure.nix;
   modifiedNixpkgsPure = import ./pkgs/top-level/default.nix;
@@ -71,6 +72,30 @@ self = {
       builtins.attrValues
       builtins.listToAttrs
     ];
+  # FIXME: currently impure
+  # NOTE: to run, you need to evaluate outputs.nix instead of default.nix
+  #       nix-shell outputs.nix -A update
+  update = let
+    updateScript = (self.packagesForSystem (builtins.currentSystem)).den-update-script;
+  in updateScript {
+    path = "";
+    packages = lib.pipe ./update-list.nix [
+      import
+      (x: x self)
+      lib.attrsToList
+      (lib.imap1 (i: {name, value}: {
+        name = builtins.toString i;
+        value = value // {
+          # hack to pass isDerivation check in nixpkgs maintainers/scripts/update.nix
+          # https://github.com/NixOS/nixpkgs/blob/a1185f4064c18a5db37c5c84e5638c78b46e3341/maintainers/scripts/update.nix#L85
+          type = "derivation";
+          name = name;
+        };
+      }))
+      builtins.listToAttrs
+      lib.recurseIntoAttrs
+    ];
+  };
 };
 
 in self