chore: initial commit

lib/package/default.nix

@@ -0,0 +1,51 @@
+{ core-inputs
+, user-inputs
+, snowfall-lib
+}:
+
+let
+  inherit (core-inputs.nixpkgs.lib) assertMsg foldl;
+
+  user-packages-root = snowfall-lib.fs.get-file "packages";
+in
+{
+  package = {
+    # Create flake output packages.
+    # Type: Attrs -> Attrs
+    # Usage: create-packages { inherit channels; src = ./my-packages; overrides = { inherit another-package; default = "my-package"; }; }
+    #   result: { another-package = ...; my-package = ...; default = ...; }
+    create-packages =
+      { channels
+      , src ? user-packages-root
+      , overrides ? { }
+      }:
+      let
+        user-packages = snowfall-lib.fs.get-default-nix-files-recursive src;
+        create-package-metadata = package: {
+          name = builtins.unsafeDiscardStringContext (snowfall-lib.path.get-parent-directory package);
+          drv = channels.nixpkgs.callPackage package {
+            inherit channels;
+            lib = snowfall-lib.internal.system-lib;
+          };
+        };
+        packages-metadata = builtins.map create-package-metadata user-packages;
+        merge-packages = packages: metadata:
+          packages // {
+            ${metadata.name} = metadata.drv;
+          };
+        packages-without-default = foldl merge-packages { } packages-metadata;
+        default-package =
+          if overrides.default or null == null then
+            { }
+          else if builtins.isAttrs overrides.default then
+            { default = overrides.default; }
+          else if packages-without-default.${overrides.default} or null != null then
+            { default = packages-without-default.${overrides.default}; }
+          else
+            { };
+        overrides-without-default = builtins.removeAttrs overrides [ "default" ];
+        packages = packages-without-default // default-package // overrides-without-default;
+      in
+      packages;
+  };
+}