let
  pkgs = import <nixpkgs> {};
  lib = pkgs.lib;

  hosts = import ../configuration/hosts;
  nixosHosts = lib.filterAttrs (name: host: host ? ssh) hosts;

  allGroups = lib.unique (
    lib.flatten (
      lib.mapAttrsToList (
        name: host: host.groups
      ) hosts
    )
  );

  hostsInGroup = group: 
    lib.filterAttrs (
      k: v: builtins.elem group v.groups
    ) hosts;

  hostsInAllGroups = lib.listToAttrs (
    map (
      group: lib.nameValuePair group (
        lib.attrNames (hostsInGroup group)
      )
    ) allGroups );

  mkDeploy = hostnames: pkgs.writeScript "deploy-${lib.concatStringsSep "-" hostnames}" ''
    #!${pkgs.stdenv.shell}
    set -e -o pipefail
    export PATH=/run/wrappers/bin/:${with pkgs; lib.makeBinPath [
      coreutils
      openssh
      nix
      gnutar
      findutils
      nettools
      gzip
      git
    ]}

    MODE=$1
    shift || true
    ARGS=$@

    [ "$MODE" == "" ] && MODE="switch"

    ${lib.concatMapStrings (hostname: let
      hostAttrs = nixosHosts.${hostname};
      nixosSystem = (import <nixpkgs/nixos/lib/eval-config.nix> {
        modules = [
          "${toString ../configuration}/hosts/${hostname}/configuration.nix"
        ];
        system = if hostAttrs ? system then hostAttrs.system else "x86_64-linux";
      }).config.system.build.toplevel;
    in ''
      (
        echo "deploying ${hostname}..."
        nix copy --no-check-sigs -s --to ssh://${hostAttrs.ssh.host} ${nixosSystem}
        ssh $NIX_SSHOPTS ${hostAttrs.ssh.host} "sudo nix-env -p /nix/var/nix/profiles/system -i ${nixosSystem}"
        ssh $NIX_SSHOPTS ${hostAttrs.ssh.host} "sudo /nix/var/nix/profiles/system/bin/switch-to-configuration $MODE $ARGS"
      ) &
      PID_LIST+=" $!"
    '') hostnames}

    echo "deploys started, waiting for them to finish..."

    trap "kill $PID_LIST" SIGINT
    wait $PID_LIST
  '';

in {
  deploy = (lib.mapAttrs (hostname: hostAttrs: mkDeploy [ hostname ]) nixosHosts) 
  // (lib.mapAttrs (group: hosts: mkDeploy hosts) hostsInAllGroups)
  // { all = mkDeploy (lib.attrNames nixosHosts); };
}