{ lib }:
# Importers from digga: https://github.com/divnix/digga/blob/main/src/importers.nix
# Plus the mkHomeConfigurations generator from digga: https://github.com/divnix/digga/blob/main/src/generators.nix
let
  flattenTree =
    /*
     *
       Synopsis: flattenTree _tree_

       Flattens a _tree_ of the shape that is produced by rakeLeaves.

       Output Format:
       An attrset with names in the spirit of the Reverse DNS Notation form
       that fully preserve information about grouping from nesting.

       Example input:
       ```
       {
       a = {
       b = {
       c = <path>;
       };
       };
       }
       ```

       Example output:
       ```
       {
       "a.b.c" = <path>;
       }
       ```
     *
     */
    tree:
    let
      op = sum: path: val:
        let
          pathStr = builtins.concatStringsSep "." path; # dot-based reverse DNS notation
        in
        if builtins.isPath val
        then
        # builtins.trace "${toString val} is a path"
          (sum
            // {
            "${pathStr}" = val;
          })
        else if builtins.isAttrs val
        then
        # builtins.trace "${builtins.toJSON val} is an attrset"
        # recurse into that attribute set
          (recurse sum path val)
        else
        # ignore that value
        # builtins.trace "${toString path} is something else"
          sum;

      recurse = sum: path: val:
        builtins.foldl'
          (sum: key: op sum (path ++ [ key ]) val.${key})
          sum
          (builtins.attrNames val);
    in
    recurse { } [ ] tree;

  rakeLeaves =
    /*
     *
       Synopsis: rakeLeaves _path_

       Recursively collect the nix files of _path_ into attrs.

       Output Format:
       An attribute set where all `.nix` files and directories with `default.nix` in them
       are mapped to keys that are either the file with .nix stripped or the folder name.
       All other directories are recursed further into nested attribute sets with the same format.

       Example file structure:
       ```
       ./core/default.nix
       ./base.nix
       ./main/dev.nix
       ./main/os/default.nix
       ```

       Example output:
       ```
       {
       core = ./core;
       base = base.nix;
       main = {
       dev = ./main/dev.nix;
       os = ./main/os;
       };
       }
       ```
     *
     */
    dirPath:
    let
      seive = file: type:
        # Only rake `.nix` files or directories
        (type == "regular" && lib.hasSuffix ".nix" file) || (type == "directory");

      collect = file: type: {
        name = lib.removeSuffix ".nix" file;
        value =
          let
            path = dirPath + "/${file}";
          in
          if
            (type == "regular")
            || (type == "directory" && builtins.pathExists (path + "/default.nix"))
          then path
          # recurse on directories that don't contain a `default.nix`
          else rakeLeaves path;
      };

      files = lib.filterAttrs seive (builtins.readDir dirPath);
    in
    lib.filterAttrs (n: v: v != { }) (lib.mapAttrs' collect files);

  flattenLeaves = dir: flattenTree (rakeLeaves dir);

  getFqdn = c:
    let
      net = c.config.networking;
      fqdn =
        if (net ? domain) && (net.domain != null)
        then "${net.hostName}.${net.domain}"
        else net.hostName;
    in
    fqdn;
in
{
  inherit rakeLeaves flattenTree flattenLeaves;

  leaves = dir: builtins.attrValues (flattenLeaves dir);

  mkHomeConfigurations = systemConfigurations:
    /*
     *
       Synopsis: mkHomeConfigurations _systemConfigurations_

       Generate the `homeConfigurations` attribute expected by `home-manager` cli
       from _nixosConfigurations_ or _darwinConfigurations_ in the form
       _user@hostname_.
     *
     */
    let
      op = attrs: c:
        attrs
        // (
          lib.mapAttrs'
            (user: v: {
              name = "${user}@${getFqdn c}";
              value = v.home;
            })
            c.config.home-manager.users
        );
      mkHmConfigs = lib.foldl op { };
    in
    mkHmConfigs (builtins.attrValues systemConfigurations);

}
