nix_config/flake.nix

{
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
    nixpkgs.url = "github:nixos/nixpkgs/nixos-25.05";
  };

  outputs = {
    self,
    nixpkgs,
    flake-utils,
  }: let
    mapOverlayOverride = namespace: overlay: final: prev: let
      overlayPkgs = overlay final prev;
    in
      {
        "${namespace}" = builtins.removeAttrs overlayPkgs ["override"];
      }
      // (overlayPkgs.override or {});

    doctrineNoPkgs = self.lib.mkDoctrine {
      lib = nixpkgs.lib;
      pkgs = null;
    };
  in
    flake-utils.lib.eachDefaultSystem (system: let
      pkgs = import nixpkgs {inherit system;};
    in {
      formatter = pkgs.alejandra;

      packages =
        (import nixpkgs {
          inherit system;
          overlays = [(mapOverlayOverride doctrineNoPkgs.prefix (import ./pkgs))];
        }).${
          doctrineNoPkgs.prefix
        };
    })
    // {
      templates = let
        system-flake = {
          path = ./templates/system-flake;
          description = "Opinionated flake for a NixOS system with Home Manager";
        };
      in {
        inherit system-flake;

        default = system-flake;
      };

      overlays = let
        overlay = mapOverlayOverride doctrineNoPkgs.prefix (import ./pkgs);
      in {
        default = overlay;
        ${doctrineNoPkgs.prefix} = overlay;
      };

      homeManagerModules.default = ./modules;
      nixosModules.default = ./modules;

      lib = {
        mkDoctrine = import ./doctrine;

        mkSystemFlake = {
          flakes,
          system,
          doctrinePrefix ? null,
          formatter ? "alejandra",
          paths ? {},
        }: let
          mkDoctrine = args:
            self.lib.mkDoctrine
            (args
              // optionalAttrs (doctrinePrefix != null) {
                prefix = doctrinePrefix;
              });

          doctrineNoPkgs = mkDoctrine {
            lib = nixpkgs.lib;
            pkgs = null;
          };

          optionalFlake = name:
            if flakes ? "${name}"
            then flakes.${name}
            else null;

          requireFlake = name:
            if flakes ? "${name}"
            then flakes.${name}
            else throw "Required flake input '${name}' is missing";

          nur = optionalFlake "nur";
          nixpkgs = requireFlake "nixpkgs";
          unstable = optionalFlake "unstable";

          home-manager =
            if hmSourcePath != null
            then requireFlake "home-manager"
            else null;

          pathFromSelf = path: builtins.toPath "${flakes.self}" + "/${path}";

          localOverlayPath = pathFromSelf paths.localOverlay;
          nixpkgsConfigPath = pathFromSelf paths.nixpkgsConfig;
          nixosSourcePath = pathFromSelf paths.nixosSource;
          nixosPlatformsPath = pathFromSelf paths.nixosPlatforms;
          hmSourcePath = pathFromSelf paths.hmSource;
          hmPlatformsPath = pathFromSelf paths.hmPlatforms;

          pkgs = importPkgs nixpkgs;

          importPkgs = flake:
            import flake ({
                inherit system;

                overlays = let
                  conditions = [
                    {
                      overlay = nur.overlays.default;
                      condition = nur != null;
                    }
                    # NB: Preserve the relative order
                    {
                      overlay = self.overlays.default;
                      condition = true;
                    }
                    {
                      overlay = flakes.self.overlays.default;
                      condition = true;
                    }
                  ];
                in
                  builtins.map (cond: cond.overlay) (builtins.filter (cond: cond.condition) conditions);
              }
              // optionalAttrs (paths ? nixpkgsConfig) {
                config = import nixpkgsConfigPath {inherit (nixpkgs) lib;};
              });

          inherit (pkgs) lib;
          inherit (nixpkgs.lib) optionalAttrs; # Prevents infinite recursion
          inherit (doctrineNoPkgs) prefix;
          inherit (doctrineNoPkgs.lib) importAll;
        in
          {
            formatter.${system} =
              if formatter == "alejandra"
              then pkgs.alejandra
              else if formatter == "nixpkgs-fmt"
              then pkgs.nixpkgs-fmt
              else throw "Unknown formatter: '${formatter}'";

            packages.${system} = pkgs.${prefix};

            overlays.default = final: prev: let
              overlay = final: prev:
                if paths ? localOverlay
                then import localOverlayPath {inherit final prev flakes;}
                else {};
            in
              mapOverlayOverride prefix overlay final prev
              // optionalAttrs (unstable != null) {
                unstable = importPkgs unstable;
              };
          }
          // optionalAttrs (paths ? nixosSource) {
            nixosConfigurations = let
              nixosSystem = {modules}:
                lib.makeOverridable nixpkgs.lib.nixosSystem {
                  inherit modules pkgs system;

                  specialArgs = {
                    inherit flakes;

                    doctrine = mkDoctrine {
                      inherit pkgs;
                      namespace = "sys";
                    };
                  };
                };

              hostConfig = platform:
                nixosSystem {
                  modules = [
                    self.nixosModules.default
                    nixosSourcePath
                    platform
                  ];
                };
            in
              lib.mapAttrs (_: hostConfig) (importAll {root = nixosPlatformsPath;});
          }
          // optionalAttrs (paths ? hmSource) {
            homeConfigurations = let
              home = name: platform:
                home-manager.lib.homeManagerConfiguration {
                  inherit pkgs;

                  extraSpecialArgs = {
                    inherit flakes;

                    doctrine = mkDoctrine {
                      inherit pkgs;
                      namespace = "hm";
                    };
                  };

                  modules = [
                    self.homeManagerModules.default
                    hmSourcePath
                    platform
                  ];
                };
            in
              lib.mapAttrs home (importAll {root = hmPlatformsPath;});
          };
      };
    };
}