# 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;
}