feat(nix): add flake templates

Signed-off-by: Seongmin Lee <[e-mail]>

nix/flake.nix

···
         pkgs.slack
       ] else []);
     };
+    # This can be just `imports = [ ./templates/templates.nix ]` when using flake-parts
+    templates = ((import ./templates/templates.nix) { inherit inputs; }).flake.templates;
   };
 }
 # vim: et:ts=2

nix/templates/python/flake.nix

···
+{
+  description = "python flake";
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+  };
+  outputs = inputs @ { flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "aarch64-darwin"
+      ];
+      perSystem = { pkgs, system, ... }: let
+        commonPackages = [
+          pkgs.python313Full
+          pkgs.pyright
+          pkgs.uv
+          pkgs.curl
+          pkgs.wget
+          pkgs.cmake
+        ] ++ pkgs.lib.optionals pkgs.stdenv.isLinux [
+          pkgs.gcc
+          pkgs.stdenv.cc.cc.lib
+        ];
+      in {
+        devShells.default = pkgs.mkShell {
+          buildInputs = commonPackages;
+          shellHook = ''
+            # Set up the Python virtual environment with uv
+            test -d .venv || ${pkgs.uv}/bin/uv venv .venv
+            export VIRTUAL_ENV="$(pwd)/.venv"
+            export PATH="$VIRTUAL_ENV/bin:$PATH"
+            export LD_LIBRARY_PATH=${pkgs.lib.makeLibraryPath commonPackages}:$LD_LIBRARY_PATH
+
+            source "$VIRTUAL_ENV/bin/activate"
+
+            if uv sync --frozen; then
+              package_count=$(uv pip list --format=freeze | wc -l)
+              echo "Done. $package_count pip packages installed."
+            else
+              echo "Warning: An error occurred during uv sync."
+            fi
+          '';
+        };
+      };
+    };
+}

nix/templates/templates.nix

···
+{ inputs, ... }:
+let templatesDir = ./.;
+in {
+  flake.templates = let
+    mkTemplate = name: val:
+      let
+        path = templatesDir + "/${name}";
+        flake = import (path + "/flake.nix");
+      in {
+        inherit path;
+        description = flake.description;
+      };
+    templateEntities = let
+      op = _: val: val == "directory";
+      as = builtins.readDir templatesDir;
+    in inputs.nixpkgs.lib.filterAttrs op as;
+  in builtins.mapAttrs mkTemplate templateEntities;
+}