homelab-deploy/nixos/module.nix

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

let
  listenerCfg = config.services.homelab-deploy.listener;
  builderCfg = config.services.homelab-deploy.builder;

  # Generate YAML config from settings
  generatedConfigFile = pkgs.writeText "builder.yaml" (lib.generators.toYAML {} {
    repos = lib.mapAttrs (name: repo: {
      url = repo.url;
      default_branch = repo.defaultBranch;
    }) builderCfg.settings.repos;
  });

  # Use provided configFile or generate from settings
  builderConfigFile =
    if builderCfg.configFile != null
    then builderCfg.configFile
    else generatedConfigFile;

  # Build command line arguments for listener from configuration
  listenerArgs = lib.concatStringsSep " " ([
    "--hostname ${lib.escapeShellArg listenerCfg.hostname}"
    "--tier ${listenerCfg.tier}"
    "--nats-url ${lib.escapeShellArg listenerCfg.natsUrl}"
    "--nkey-file ${lib.escapeShellArg listenerCfg.nkeyFile}"
    "--flake-url ${lib.escapeShellArg listenerCfg.flakeUrl}"
    "--timeout ${toString listenerCfg.timeout}"
    "--discover-subject ${lib.escapeShellArg listenerCfg.discoverSubject}"
  ]
  ++ lib.optional (listenerCfg.role != null) "--role ${lib.escapeShellArg listenerCfg.role}"
  ++ map (s: "--deploy-subject ${lib.escapeShellArg s}") listenerCfg.deploySubjects
  ++ lib.optionals listenerCfg.metrics.enable [
    "--metrics-enabled"
    "--metrics-addr ${lib.escapeShellArg listenerCfg.metrics.address}"
  ]);

  # Build command line arguments for builder from configuration
  builderArgs = lib.concatStringsSep " " ([
    "--nats-url ${lib.escapeShellArg builderCfg.natsUrl}"
    "--nkey-file ${lib.escapeShellArg builderCfg.nkeyFile}"
    "--config ${builderConfigFile}"
    "--timeout ${toString builderCfg.timeout}"
  ]
  ++ lib.optionals builderCfg.metrics.enable [
    "--metrics-enabled"
    "--metrics-addr ${lib.escapeShellArg builderCfg.metrics.address}"
  ]);

  # Extract port from metrics address for firewall rule
  extractPort = addr: let
    # Handle both ":9972" and "0.0.0.0:9972" formats
    parts = lib.splitString ":" addr;
  in lib.toInt (lib.last parts);

  listenerMetricsPort = extractPort listenerCfg.metrics.address;
  builderMetricsPort = extractPort builderCfg.metrics.address;

in
{
  options.services.homelab-deploy.listener = {
    enable = lib.mkEnableOption "homelab-deploy listener service";

    package = lib.mkOption {
      type = lib.types.package;
      default = self.packages.${pkgs.system}.homelab-deploy;
      description = "The homelab-deploy package to use";
    };

    hostname = lib.mkOption {
      type = lib.types.str;
      default = config.networking.hostName;
      description = "Hostname for this listener (used in subject templates)";
    };

    tier = lib.mkOption {
      type = lib.types.enum [ "test" "prod" ];
      description = "Deployment tier for this host";
    };

    role = lib.mkOption {
      type = lib.types.nullOr lib.types.str;
      default = null;
      description = "Role for role-based deployment targeting";
    };

    natsUrl = lib.mkOption {
      type = lib.types.str;
      description = "NATS server URL";
      example = "nats://nats.example.com:4222";
    };

    nkeyFile = lib.mkOption {
      type = lib.types.path;
      description = "Path to NKey seed file for NATS authentication";
      example = "/run/secrets/homelab-deploy-nkey";
    };

    flakeUrl = lib.mkOption {
      type = lib.types.str;
      description = "Git flake URL for nixos-rebuild";
      example = "git+https://git.example.com/user/nixos-configs.git";
    };

    timeout = lib.mkOption {
      type = lib.types.int;
      default = 600;
      description = "Deployment timeout in seconds";
    };

    deploySubjects = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [
        "deploy.<tier>.<hostname>"
        "deploy.<tier>.all"
        "deploy.<tier>.role.<role>"
      ];
      description = ''
        List of NATS subjects to subscribe to for deployment requests.
        Template variables: <hostname>, <tier>, <role>
      '';
    };

    discoverSubject = lib.mkOption {
      type = lib.types.str;
      default = "deploy.discover";
      description = "NATS subject for host discovery requests";
    };

    environment = lib.mkOption {
      type = lib.types.attrsOf lib.types.str;
      default = { };
      description = "Additional environment variables for the service";
      example = { GIT_SSH_COMMAND = "ssh -i /run/secrets/deploy-key"; };
    };

    metrics = {
      enable = lib.mkEnableOption "Prometheus metrics endpoint";

      address = lib.mkOption {
        type = lib.types.str;
        default = ":9972";
        description = "Address for Prometheus metrics HTTP server";
        example = "127.0.0.1:9972";
      };

      openFirewall = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Open firewall for metrics port";
      };
    };
  };

  options.services.homelab-deploy.builder = {
    enable = lib.mkEnableOption "homelab-deploy builder service";

    package = lib.mkOption {
      type = lib.types.package;
      default = self.packages.${pkgs.system}.homelab-deploy;
      description = "The homelab-deploy package to use";
    };

    natsUrl = lib.mkOption {
      type = lib.types.str;
      description = "NATS server URL";
      example = "nats://nats.example.com:4222";
    };

    nkeyFile = lib.mkOption {
      type = lib.types.path;
      description = "Path to NKey seed file for NATS authentication";
      example = "/run/secrets/homelab-deploy-builder-nkey";
    };

    configFile = lib.mkOption {
      type = lib.types.nullOr lib.types.path;
      default = null;
      description = ''
        Path to builder configuration file (YAML).
        If not specified, a config file will be generated from the `settings` option.
      '';
      example = "/etc/homelab-deploy/builder.yaml";
    };

    settings = {
      repos = lib.mkOption {
        type = lib.types.attrsOf (lib.types.submodule {
          options = {
            url = lib.mkOption {
              type = lib.types.str;
              description = "Git flake URL for the repository";
              example = "git+https://git.example.com/org/nixos-configs.git";
            };
            defaultBranch = lib.mkOption {
              type = lib.types.str;
              default = "master";
              description = "Default branch to build when not specified in request";
              example = "main";
            };
          };
        });
        default = {};
        description = ''
          Repository configuration for the builder.
          Each key is the repository name used in build requests.
        '';
        example = lib.literalExpression ''
          {
            nixos-servers = {
              url = "git+https://git.example.com/org/nixos-servers.git";
              defaultBranch = "master";
            };
            homelab = {
              url = "git+ssh://git@github.com/user/homelab.git";
              defaultBranch = "main";
            };
          }
        '';
      };
    };

    timeout = lib.mkOption {
      type = lib.types.int;
      default = 1800;
      description = "Build timeout in seconds per host";
    };

    environment = lib.mkOption {
      type = lib.types.attrsOf lib.types.str;
      default = { };
      description = "Additional environment variables for the service";
      example = { GIT_SSH_COMMAND = "ssh -i /run/secrets/deploy-key"; };
    };

    metrics = {
      enable = lib.mkEnableOption "Prometheus metrics endpoint";

      address = lib.mkOption {
        type = lib.types.str;
        default = ":9973";
        description = "Address for Prometheus metrics HTTP server";
        example = "127.0.0.1:9973";
      };

      openFirewall = lib.mkOption {
        type = lib.types.bool;
        default = false;
        description = "Open firewall for metrics port";
      };
    };
  };

  config = lib.mkMerge [
    (lib.mkIf builderCfg.enable {
      assertions = [
        {
          assertion = builderCfg.configFile != null || builderCfg.settings.repos != {};
          message = "services.homelab-deploy.builder: either configFile or settings.repos must be specified";
        }
      ];
    })

    (lib.mkIf listenerCfg.enable {
      systemd.services.homelab-deploy-listener = {
        description = "homelab-deploy listener";
        wantedBy = [ "multi-user.target" ];
        after = [ "network-online.target" ];
        wants = [ "network-online.target" ];

        # Prevent self-interruption during nixos-rebuild switch
        # The service will continue running the old version until manually restarted
        stopIfChanged = false;
        restartIfChanged = false;

        environment = listenerCfg.environment // {
          # Nix needs a writable cache for git flake fetching
          XDG_CACHE_HOME = "/var/cache/homelab-deploy";
        };

        path = [ pkgs.git config.system.build.nixos-rebuild ];

        serviceConfig = {
          CacheDirectory = "homelab-deploy";
          Type = "simple";
          ExecStart = "${listenerCfg.package}/bin/homelab-deploy listener ${listenerArgs}";
          Restart = "always";
          RestartSec = 10;

          # Minimal hardening - nixos-rebuild requires broad system access:
          # - Write access to /nix/store for building
          # - Kernel namespace support for nix sandbox builds
          # - Ability to activate system configurations
          # - Network access for fetching from git/cache
          # Following the approach of nixos auto-upgrade which has no hardening
        };
      };

      networking.firewall.allowedTCPPorts = lib.mkIf (listenerCfg.metrics.enable && listenerCfg.metrics.openFirewall) [
        listenerMetricsPort
      ];
    })

    (lib.mkIf builderCfg.enable {
      systemd.services.homelab-deploy-builder = {
        description = "homelab-deploy builder";
        wantedBy = [ "multi-user.target" ];
        after = [ "network-online.target" ];
        wants = [ "network-online.target" ];

        environment = builderCfg.environment // {
          # Nix needs a writable cache for git flake fetching
          XDG_CACHE_HOME = "/var/cache/homelab-deploy-builder";
        };

        path = [ pkgs.git pkgs.nix ];

        serviceConfig = {
          CacheDirectory = "homelab-deploy-builder";
          Type = "simple";
          ExecStart = "${builderCfg.package}/bin/homelab-deploy builder ${builderArgs}";
          Restart = "always";
          RestartSec = 10;

          # Minimal hardening - nix build requires broad system access:
          # - Write access to /nix/store for building
          # - Kernel namespace support for nix sandbox builds
          # - Network access for fetching from git/cache
        };
      };

      networking.firewall.allowedTCPPorts = lib.mkIf (builderCfg.metrics.enable && builderCfg.metrics.openFirewall) [
        builderMetricsPort
      ];
    })
  ];
}