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

with lib;

let

  cfg = config.home-manager;

  extendedLib = import ../modules/lib/stdlib-extended.nix pkgs.lib;

  hmModule = types.submoduleWith {
    specialArgs = { lib = extendedLib; };
    modules = [
      ({ name, ... }: {
        imports = import ../modules/modules.nix {
          inherit pkgs;
          lib = extendedLib;
          useNixpkgsModule = !cfg.useGlobalPkgs;
        };

        config = {
          submoduleSupport.enable = true;
          submoduleSupport.externalPackageInstall = cfg.useUserPackages;

          home.username = config.users.users.${name}.name;
          home.homeDirectory = config.users.users.${name}.home;
        };
      })
    ];
  };

in

{
  options = {
    home-manager = {
      useUserPackages = mkEnableOption ''
        installation of user packages through the
        <option>users.users.‹name?›.packages</option> option.
      '';

      useGlobalPkgs = mkEnableOption ''
        using the system configuration's <literal>pkgs</literal>
        argument in Home Manager. This disables the Home Manager
        options <option>nixpkgs.*</option>
      '';

      backupFileExtension = mkOption {
        type = types.nullOr types.str;
        default = null;
        example = "backup";
        description = ''
          On activation move existing files by appending the given
          file extension rather than exiting with an error.
        '';
      };

      verbose = mkEnableOption "verbose output on activation";

      users = mkOption {
        type = types.attrsOf hmModule;
        default = {};
        description = ''
          Per-user Home Manager configuration.
        '';
      };
    };
  };

  config = mkIf (cfg.users != {}) {
    warnings =
      flatten (flip mapAttrsToList cfg.users (user: config:
        flip map config.warnings (warning:
          "${user} profile: ${warning}"
        )
      ));

    assertions =
      flatten (flip mapAttrsToList cfg.users (user: config:
        flip map config.assertions (assertion:
          {
            inherit (assertion) assertion;
            message = "${user} profile: ${assertion.message}";
          }
        )
      ));

    users.users = mkIf cfg.useUserPackages (
      mapAttrs (username: usercfg: {
        packages = [ usercfg.home.path ];
      }) cfg.users
    );

    environment.pathsToLink = mkIf cfg.useUserPackages [ "/etc/profile.d" ];

    system.activationScripts.postActivation.text =
      concatStringsSep "\n" (mapAttrsToList (username: usercfg: ''
        echo Activating home-manager configuration for ${username}
        sudo -u ${username} -i ${pkgs.writeShellScript "activation-${username}" ''
          ${lib.optionalString (cfg.backupFileExtension != null)
            "export HOME_MANAGER_BACKUP_EXT=${lib.escapeShellArg cfg.backupFileExtension}"}
          ${lib.optionalString cfg.verbose "export VERBOSE=1"}
          exec ${usercfg.home.activationPackage}/activate
        ''}
      '') cfg.users);
  };
}