{ config, lib, pkgs, ... }:

with lib;

let

  profileDirectory = config.home.profileDirectory;

in {
  options.targets.genericLinux = {
    enable = mkEnableOption "" // {
      description = ''
        Whether to enable settings that make Home Manager work better on
        GNU/Linux distributions other than NixOS.
      '';
    };

    extraXdgDataDirs = mkOption {
      type = types.listOf types.str;
      default = [ ];
      example = [ "/usr/share" "/usr/local/share" ];
      description = ''
        List of directory names to add to <envar>XDG_DATA_DIRS</envar>.
      '';
    };
  };

  config = mkIf config.targets.genericLinux.enable {
    home.sessionVariables = let
      profiles =
        [ "\${NIX_STATE_DIR:-/nix/var/nix}/profiles/default" profileDirectory ];
      dataDirs = concatStringsSep ":"
        (map (profile: "${profile}/share") profiles
          ++ config.targets.genericLinux.extraXdgDataDirs);
    in { XDG_DATA_DIRS = "${dataDirs}\${XDG_DATA_DIRS:+:}$XDG_DATA_DIRS"; };

    home.sessionVariablesExtra = ''
      . "${pkgs.nix}/etc/profile.d/nix.sh"
    '';

    # We need to source both nix.sh and hm-session-vars.sh as noted in
    # https://github.com/nix-community/home-manager/pull/797#issuecomment-544783247
    programs.bash.initExtra = ''
      . "${pkgs.nix}/etc/profile.d/nix.sh"
      . "${profileDirectory}/etc/profile.d/hm-session-vars.sh"
    '';

    systemd.user.sessionVariables = {
      NIX_PATH = "$HOME/.nix-defexpr/channels\${NIX_PATH:+:}$NIX_PATH";
    };
  };
}