# roles/thin-client/identity/ad.nix
#
# Active Directory integration for Thin Clients.
#
# Real realm: AZ-GROUP
# DNS domain: az-group.local
# Join mechanism: Pre-created computer accounts + keytab via agenix
#   (no interactive realm join, no service account with join privileges).
#
# Provisioning per host (admin-side, one-shot):
#   1. adcli precreate --computer-name=AZ-TC-01$ \
#        --domain=az-group.local \
#        --host-fqdn=AZ-TC-01.az-group.local \
#        --login-type=computer \
#        --os-name="NixOS" --os-version="25.11" \
#        --domain-ou="OU=ThinClients,DC=az-group,DC=local" \
#        <admin>@AZ-GROUP
#   2. adcli join --computer-name=AZ-TC-01$ \
#        --domain=az-group.local \
#        --host-fqdn=AZ-TC-01.az-group.local \
#        --login-type=computer \
#        --user=<admin> --verbose \
#        -K /tmp/AZ-TC-01.keytab
#   3. agenix -e secrets/AZ-TC-01-krb5-keytab.age  (paste /tmp/AZ-TC-01.keytab)
#   4. rm /tmp/AZ-TC-01.keytab
#   5. Deploy; the keytab decrypts to /etc/krb5.keytab on the host.
#
# SSSD resolves users/groups via AD; kerberos auth via keytab for the
# machine account. User login uses their AD password (offline-capable via
# cache_credentials=true).
{
  config,
  lib,
  pkgs,
  ...
}: let
  cfg = config.az.tc;
  hostname = config.networking.hostName;
  domain = "az-group.local";
  realm = "AZ-GROUP";
in {
  options.az.tc.ad = {
    ou = lib.mkOption {
      type = lib.types.str;
      default = "OU=ThinClients,DC=az-group,DC=local";
      description = ''
        AD Organizational Unit where Thin Client computer objects live.
        Override if your AD layout differs. Used for documentation and
        the pre-create workflow; not consumed at runtime.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    environment.systemPackages = with pkgs; [
      adcli
      sssd
      samba4Full
      krb5
      realmd
      oddjob
    ];

    # Kerberos client
    security.krb5 = {
      enable = true;
      settings = {
        libdefaults = {
          default_realm = realm;
          udp_preference_limit = 0;
          forwardable = true;
          proxiable = true;
          rdns = false;
        };
        domain_realm = {
          ".az-group.local" = realm;
          "az-group.local" = realm;
        };
        realms = {
          "${realm}" = {
            kdc = ["az-dc01.az-group.local" "az-dc02.az-group.local"];
            admin_server = "az-dc01.az-group.local";
          };
        };
      };
    };

    # PAM: create per-user /home on first login (used by domain users)
    security.pam = {
      services.login.makeHomeDir = true;
      services.sddm.makeHomeDir = true;
      services.sshd.makeHomeDir = true;
      makeHomeDir.umask = "077";
    };

    services.nscd.enable = true;

    services.sssd = {
      enable = true;
      config = ''
        [sssd]
        domains = az-group.local
        config_file_version = 2
        services = nss, pam

        [domain/az-group.local]
        id_provider = ad
        auth_provider = ad
        access_provider = ad
        chpass_provider = ad
        ad_domain = ${domain}
        ad_server = az-dc01.az-group.local, az-dc02.az-group.local
        krb5_realm = ${realm}
        krb5_server = az-dc01.az-group.local, az-dc02.az-group.local
        krb5_keytab = /etc/krb5.keytab
        krb5_store_password_if_offline = True
        cache_credentials = True
        use_fully_qualified_names = false
        fallback_homedir = /home/%u
        override_shell = /run/current-system/sw/bin/bash
        default_shell = /run/current-system/sw/bin/bash
        ad_gpo_access_control = permissive
        enumerate = true
        ldap_id_mapping = false
      '';
    };

    # DNS — Thin Clients use AD DCs as resolver (NetBird DNS overlays
    # for corp-VPN-only domains via systemd-resolved; see network/dns.nix)
    networking.nameservers = lib.mkDefault ["az-dc01.az-group.local" "az-dc02.az-group.local"];
    networking.domain = lib.mkDefault domain;
    networking.search = lib.mkDefault [domain];

    # Host FQDN — important for Kerberos SPN matching.
    # `networking.hostName` is set by the host's default.nix; here we
    # only add the hosts file fallback so the FQDN resolves locally even
    # before DNS is reachable.
    networking.extraHosts = ''
      127.0.0.1 ${hostname}.${domain} ${hostname}
    '';

    # agenix-deployed machine keytab
    age.secrets."${hostname}-krb5-keytab" = {
      file = ../../secrets/${hostname}-krb5-keytab.age;
      path = "/etc/krb5.keytab";
      mode = "0600";
      owner = "root";
      group = "root";
    };

    # Ensure keytab path is readable by sssd (runs as root) but not by
    # anyone else.
    systemd.services.sssd = {
      after = ["age-identity.service"];
      wants = ["age-identity.service"];
      serviceConfig.ExecStartPre = let
        check = pkgs.writeShellScript "check-keytab" ''
          if [ ! -s /etc/krb5.keytab ]; then
            echo "ERROR: /etc/krb5.keytab is empty or missing." >&2
            echo "Provision via adcli join + agenix, see roles/thin-client/README.md." >&2
            exit 1
          fi
        '';
      in ["+${check}"];
    };
  };
}