{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  };

  outputs = { self, nixpkgs }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};

      # Python with custom packages
      python = pkgs.python313.override {
        self = python;
        packageOverrides = pyfinal: pyprev: {
          # Leaf packages (no custom dependencies)
          mistletoe = pyfinal.callPackage ./packages/mistletoe.nix { };
          sse-starlette = pyfinal.callPackage ./packages/sse-starlette.nix { };
          fastcore = pyfinal.callPackage ./packages/fastcore.nix { };

          # Second level (depend on leaf packages)
          apswutils = pyfinal.callPackage ./packages/apswutils.nix { };
          fastlite = pyfinal.callPackage ./packages/fastlite.nix { };
          fastmigrate = pyfinal.callPackage ./packages/fastmigrate.nix { };

          # Top level (depend on second level)
          python-fasthtml = pyfinal.callPackage ./packages/python-fasthtml.nix { };
          monsterui = pyfinal.callPackage ./packages/monsterui.nix { };
        };
      };

      # Shared Python environment for both dev and Docker
      pythonEnv = python.withPackages (ps: with ps; [
        # From nixpkgs
        uvicorn
        starlette
        httpx
        pydantic
        pydantic-settings
        anyio
        beautifulsoup4
        python-dateutil
        oauthlib
        itsdangerous
        python-multipart
        lxml
        apsw
        packaging
        python-ulid
        xxhash

        # Custom packages
        fastcore
        apswutils
        fastlite
        fastmigrate
        sse-starlette
        python-fasthtml
        monsterui
        mistletoe

        # Dev-only (not needed in Docker, but fine to include)
        pytest
        pytest-xdist
        ruff
        filelock
      ]);
    in
    {
      packages.${system} = {
        dockerImage = let
          buildDate = let
            d = self.lastModifiedDate or "00000000000000";
          in "${builtins.substring 0 4 d}-${builtins.substring 4 2 d}-${builtins.substring 6 2 d}";
          buildCommit = self.shortRev or self.dirtyShortRev or "unknown";
        in import ./docker.nix { inherit pkgs pythonEnv python buildDate buildCommit; };
      };

      devShells.${system}.default = pkgs.mkShell {
        buildInputs = [
          pythonEnv

          # Tools
          pkgs.jq
          pkgs.sqlite
          pkgs.skopeo  # For pushing Docker images
          pkgs.lefthook  # Git hooks manager
        ];

        shellHook = ''
          export PYTHONPATH="$PWD/src:$PYTHONPATH"
          export PATH="$PWD/bin:$PATH"
          echo "AnimalTrack development environment ready!"
          echo "Run 'animaltrack serve' to start the app"
        '';
      };
    };
}