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

with lib;

let
  # TODO: move to flake
  nixcloud-webservices = pkgs.fetchFromGitHub {
    owner = "nixcloud";
    repo = "nixcloud-webservices";
    rev = "3a0767f0536fac811065eb87e6342f27eac085aa";
    sha256 = "vC0vBu+0HchrevuWsmE7giouKnSt/q4F0TffwhuNJv8=";
  };
  inherit (import "${nixcloud-webservices}/pkgs" { inherit pkgs; }) nixcloud;

  profilesDir = "/nix/var/nix/profiles/lxc";
  inherit (config.lxc) containers;
  inherit (config.nix) nixPath;

  toLxcConfig' = path: a:
    if builtins.isString a then ''
      ${path} = ${a}
    '' else if builtins.isInt a then ''
      ${path} = ${toString a}
    '' else if builtins.isAttrs a then
      lib.concatMapStrings (name:
        let path' = if path == "" then name else "${path}.${name}";
        in toLxcConfig' path' (builtins.getAttr name a)) (builtins.attrNames a)
    else if builtins.isList a then
      lib.concatMapStrings (toLxcConfig' path) a
    else
      throw "Invalid LXC config value";
  toLxcConfig = toLxcConfig' "";

  lxc-rootfs = pkgs.runCommand "lxc-rootfs" { } ''
    mkdir -p $out/share/lxc/rootfs/{dev,nix/store,proc,run,sys,tmp}
  '';
in {
  options = with types; {
    lxc.containers = mkOption {
      type = attrs;
      default = { };
    };
  };

  config = mkIf (containers != { }) {
    virtualisation.lxc.enable = true;
    environment.systemPackages = [ nixcloud.container ];

    virtualisation.lxc.defaultConfig = ''
      lxc.id_map = u 0 100000 65536
      lxc.id_map = g 0 100000 65536
    '';
    users.users.root.subGidRanges = [{
      count = 65536;
      startGid = 100000;
    }];
    users.users.root.subUidRanges = [{
      count = 65536;
      startUid = 100000;
    }];

    systemd.services = if true then
      { }
    else
      builtins.foldl' (services: name:
        let
          systemDir = "/${profilesDir}/${name}/system";
          lxcDefaults = {
            lxc = {
              uts.name = name;
              rootfs.path = "/run/current-system/sw/share/lxc/rootfs";
              mount.entry = [
                "${systemDir}/init /init none bind,ro 0 0"
                "/nix/store /nix/store none bind,ro 0 0"
              ];
              autodev = 1;
              include = "/run/current-system/sw/share/lxc/config/common.conf";
              apparmor.profile = "generated";
              environment = "TERM=linux";
            };
          };
          config = builtins.getAttr name containers;
          lxcConfig = builtins.toFile "lxc-container-${name}.conf"
            # TODO: more intelligent merging?
            (toLxcConfig (lxcDefaults // config.lxc));

          builder = {
            description = "Build NixOS for lxc container ${name}";
            wants = [ "nix-daemon.socket" ];
            after = [ "nix-daemon.service" ];

            path = with pkgs; [ coreutils nix ];

            serviceConfig = {
              Type = "oneshot";
              RemainAfterExit = true;
              Environment = [ "NIX_PATH=${builtins.concatStringsSep ":" nixPath}" ];
            };

            script = ''
              mkdir -p ${profilesDir}/${name}

              nix-env -p ${profilesDir}/${name}/system \
                -I nixos-config=${config.nixos-config} \
                -f '<nixpkgs/nixos>' \
                --set -A system
            '';
          };
          starter = {
            description = "LXC container ${name}";
            requires = [ "lxc-container-${name}-builder.service" ];
            after = [ "lxc-container-${name}-builder.service" ];

            path = with pkgs; [ lxc apparmor-parser ];

            script = ''
              mkdir -p /var/lib/lxc/${name}
              ln -fs ${lxcConfig} /var/lib/lxc/${name}/config
              lxc-start -F -n ${name}
            '';
          };
        in services // {
          "lxc-container-${name}-builder" = builder;
          "lxc-container-${name}" = starter;
        }) { } (builtins.attrNames containers);
  };
}