From 727d5ab1edd02ccede4d56ce7c27b036ef4353e2 Mon Sep 17 00:00:00 2001
From: Yipeng Sun <syp@umd.edu>
Date: Thu, 19 Sep 2024 17:15:20 +0800
Subject: [PATCH] WIP #14: naive systemBuilder stolen from lite-config.

---
 lib/systemBuilder.nix | 196 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 196 insertions(+)
 create mode 100644 lib/systemBuilder.nix

diff --git a/lib/systemBuilder.nix b/lib/systemBuilder.nix
new file mode 100644
index 0000000..553fd5d
--- /dev/null
+++ b/lib/systemBuilder.nix
@@ -0,0 +1,196 @@
+# stolen from `lite-config`:
+#   https://github.com/yelite/lite-config
+#
+# build NixOS/darwin systems
+
+{ inputs
+, lib
+, withSystem
+, ...
+} @ toplevel:
+let
+  inherit (builtins)
+    attrValues
+    foldl'
+    ;
+
+  inherit (lib)
+    mapAttrs
+    mkOption
+    types
+    literalExpression
+    recursiveUpdateUntil
+    ;
+
+
+  cfgSupport = toplevel.config.localNixpkgs; # external config options
+  cfg = toplevel.config.systemBuilder; # shortcut to user config
+
+
+  # types in config
+  typeHostConfig = types.submodule {
+    options = {
+      system = mkOption {
+        type = types.str;
+        description = ''
+          The system of the host.
+        '';
+        example =
+          literalExpression
+            ''
+              "x86_64-linux"
+            '';
+      };
+
+      systemSuites = mkOption {
+        type = types.listOf types.deferredModule;
+        default = [ ];
+        description = ''
+          System suites (NixOS or nix-darwin) to be imported by this host.
+        '';
+      };
+
+      homeSuites = mkOption {
+        type = types.listOf types.deferredModule;
+        default = [ ];
+        description = ''
+          Home suites to be imported by this host.
+        '';
+      };
+    };
+  };
+
+  typeSystemBuilderOptions = types.submodule {
+    options = {
+      hosts = mkOption {
+        type = types.attrsOf typeHostConfig;
+        default = { };
+        description = ''
+          Host configurations.
+        '';
+      };
+
+      hostModuleDir = mkOption {
+        type = types.path;
+        description = ''
+          The directory that contains host modules. Module at
+          `''${hostMouduleDir}/''${hostName}` will be imported in
+          the configuration of host `hostName` by default.
+
+          The host module used by a host can be overridden in
+          {option}`lite-config.hosts.<hostName>.hostModule`.
+        '';
+      };
+
+      nixosModules = mkOption {
+        type = types.listOf types.deferredModule;
+        default = [ ];
+        description = ''
+          NixOS modules to be imported by all NixOS hosts.
+        '';
+      };
+
+      darwinModules = mkOption {
+        type = types.listOf types.deferredModule;
+        default = [ ];
+        description = ''
+          Darwin modules to be imported by all Darwin hosts.
+        '';
+      };
+
+      homeModules = mkOption {
+        type = types.listOf types.deferredModule;
+        default = [ ];
+        description = ''
+          Home modules to be imported by all hosts.
+        '';
+      };
+    };
+  };
+
+
+  # helper functions
+  errUnsupportedSys = system: throw "System type ${system} not supported.";
+
+
+  # the actual builder
+  systemBuilder = hostName: hostConfig:
+    withSystem hostConfig.system ({ pkgs, ... }:
+      let
+        hostPlatform = pkgs.stdenv.hostPlatform;
+        hostModule = "${cfg.hostModuleDir}/${hostName}";
+
+        systemModules =
+          if hostPlatform.isLinux then cfg.nixosModules
+          else if hostPlatform.isDarwin then cfg.darwinModules
+          else errUnsupportedSys hostPlatform.system;
+
+        homeManagerFlake = inputs.home-manager;
+        homeManagerSystemModule =
+          if hostPlatform.isLinux then homeManagerFlake.nixosModules.default
+          else if hostPlatform.isDarwin then homeManagerFlake.darwinModules.default
+          else errUnsupportedSys hostPlatform.system;
+
+        specialArgs = {
+          inherit inputs hostPlatform;
+        };
+
+        modules = [
+          hostModule
+          {
+            _file = ./.;
+            nixpkgs.pkgs = pkgs;
+            networking.hostName = hostName;
+          }
+        ]
+        ++ systemModules ++ hostConfig.systemSuites
+        ++
+        [
+          homeManagerSystemModule
+          {
+            _file = ./.;
+            home-manager = {
+              sharedModules = cfg.homeModules ++ hostConfig.homeSuites;
+              useGlobalPkgs = true;
+              extraSpecialArgs = specialArgs;
+            };
+          }
+        ];
+
+        # aggregated args
+        builderArgs = { inherit specialArgs modules; };
+      in
+      if hostPlatform.isLinux
+      then {
+        nixosConfiguration.${hostName} = cfgSupport.nixpkgs.lib.nixosSystem builderArgs;
+      }
+      else if hostPlatform.isDarwin
+      then {
+        # NOTE: hard-coded darwin builder
+        darwinConfiguration.${hostName} = inputs.nix-darwin.lib.darwinSystem builderArgs;
+      }
+      else errUnsupportedSys hostPlatform.system);
+
+  systemAttrset =
+    let
+      mergeSysConfig = a: b: recursiveUpdateUntil (path: _: _: (length path) > 2) a b;
+      sysConfigAttrsets = attrValues (mapAttrs systemBuilder cfg.hosts);
+    in
+    foldl' mergeSysConfig { } sysConfigAttrsets;
+in
+{
+  options = {
+    systemBuilder = mkOption {
+      type = typeSystemBuilderOptions;
+      default = { };
+      description = ''
+        Config for NixOS/Darwin systems.
+      '';
+    };
+  };
+
+
+  config = {
+    flake = systemAttrset;
+  };
+}