Trying to structure this to be a flake input.

flake.nix

@@ -0,0 +1,38 @@
+{
+  description = "Metanix infra logic flake";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = { self, nixpkgs }:
+    let
+      system = "x86_64-linux";
+      pkgs = import nixpkgs { inherit system; };
+      data = import ./meta.nix;
+      metanix = import ./lib/metanix.nix { inherit data; lib = pkgs.lib; };
+    in
+    {
+      # You get a devShell so you can :repl in peace
+      devShells.${system}.default = pkgs.mkShell {
+        buildInputs = [ pkgs.nix pkgs.git ];
+      };
+
+      # Simple command to dump the system index to stdout
+      apps.${system}.print-index = {
+        type = "app";
+        program = pkgs.writeShellScript "print-index" ''
+          nix eval --impure --expr '
+            let
+              data = import ./meta.nix;
+              lib = import ${nixpkgs}/lib;
+              metanix = import ./lib/metanix.nix { inherit data lib; };
+            in
+              builtins.toJSON metanix.buildSystemIndex
+          '
+        '';
+      };
+
+      # Or expose it as a Nix eval-friendly output
+      packages.${system}.default = pkgs.writeText "system-index.json"
+        (builtins.toJSON metanix.buildSystemIndex);
+    };
+}

lib/metanix.nix

@@ -0,0 +1,45 @@
+# lib/metanix.nix
+{ data, lib }:
+
+let
+  buildSystemIndex =
+    let
+      flattenSystems = locationName: subnetName: systems:
+        lib.mapAttrsToList
+          (systemName: systemCfg: {
+            inherit systemName locationName subnetName;
+            primary = systemCfg.primary or false;
+            macs = systemCfg.macAddresses or [ ];
+          })
+          systems;
+
+      allSystems =
+        builtins.concatLists (
+          lib.mapAttrsToList
+            (locationName: location:
+              builtins.concatLists (
+                lib.mapAttrsToList
+                  (subnetName: subnet:
+                    flattenSystems locationName subnetName (subnet.systems or { })
+                  )
+                  (location.subnets or { })
+              )
+            )
+            data.locations
+        );
+    in
+    builtins.foldl'
+      (acc: entry:
+        let
+          existing = acc.${entry.systemName} or [ ];
+        in
+        acc // {
+          ${entry.systemName} = existing ++ [ builtins.removeAttrs entry [ "systemName" ] ];
+        }
+      )
+      { }
+      allSystems;
+in
+{
+  inherit buildSystemIndex;
+}

test-index.nix

@@ -0,0 +1,6 @@
+# test-index.nix
+let
+  data = import ./meta.nix;
+  metanix = import ./lib/metanix.nix { inherit data; };
+in
+metanix.buildSystemIndex