Add Nix flake (WIP)

flake.nix

@@ -0,0 +1,63 @@
+{
+  description = "Cashu is a Chaumian Ecash wallet and mint for Bitcoin Lightning.";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
+  inputs.poetry2nix = {
+    # the most recent poetry2nix seems to have a bug, we pin to an earlier version
+    url = "github:nix-community/poetry2nix/2023.10.05.49422";
+    inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    poetry2nix,
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      # see https://github.com/nix-community/poetry2nix/tree/master#api for more functions and examples.
+      inherit (poetry2nix.legacyPackages.${system}) mkPoetryApplication;
+      pkgs = import nixpkgs { inherit system; };
+    in {
+      packages = {
+        cashu =
+          (mkPoetryApplication {
+            projectDir = ./.;
+            # don't check dev deps
+            checkGroups = [];
+            overrides = pkgs.poetry2nix.overrides.withDefaults (final: prev: {
+              urllib3 = prev.urllib3.overridePythonAttrs (old: {
+                nativeBuildInputs = old.nativeBuildInputs ++ [final.hatchling];
+              });
+              attrs = prev.attrs.overridePythonAttrs (old: {
+                nativeBuildInputs = old.nativeBuildInputs ++ [final.hatchling final.hatch-fancy-pypi-readme final.hatch-vcs];
+              });
+              cryptography = prev.cryptography.override {preferWheel = true;};
+              bip32 = prev.buildPythonPackage {
+                name = "bip32";
+                propagatedBuildInputs = with final; [coincurve base58];
+                nativeBuildInputs = with final; [setuptools hatchling];
+                src = pkgs.fetchFromGitHub {
+                  owner = "darosior";
+                  repo = "python-bip32";
+                  rev = "1492d39312f1d9630363c292f6ab8beb8ceb16dd";
+                  sha256 = "sha256-o8UKR17XDWp1wTWYeDL0DJY+D11YI4mg0UuGEAPkHxE=";
+                };
+              };
+            });
+          })
+          .overridePythonAttrs (old: {
+            propagatedBuildInputs = old.propagatedBuildInputs ++ [pkgs.python3Packages.setuptools];
+            nativeBuildInputs = old.nativeBuildInputs ++ [pkgs.python3Packages.pythonRelaxDepsHook ];
+            pythonRelaxDeps = ["setuptools"];
+          });
+        default = self.packages.${system}.cashu;
+      };
+
+      devShells.default = pkgs.mkShell {
+        packages = [poetry2nix.packages.${system}.poetry];
+        buildInputs = with pkgs; [pkg-config];
+      };
+    });
+}