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

with lib;

let
  cfg = config.services.naxos.appEngine;
in {
  options.services.naxos.appEngine = {
    enable = mkEnableOption "NaxOS Multi-Tier App Engine";

    defaultRuntime = mkOption {
      type = types.enum [ "systemd" "docker" "k3s" ];
      default = "docker";
      description = "Default execution runtime for user workloads.";
    };

    docker = {
      enable = mkOption {
        type = types.bool;
        default = true;
        description = "Enable Docker engine for containerized applications.";
      };
      storageDriver = mkOption {
        type = types.enum [ "zfs" "overlay2" "btrfs" ];
        default = "zfs";
        description = "Container storage driver. 'zfs' uses native copy-on-write datasets.";
      };
      dataRoot = mkOption {
        type = types.str;
        default = "/var/lib/docker";
        description = "Storage root for container images and layers.";
      };
    };

    k3s = {
      enable = mkOption {
        type = types.bool;
        default = false;
        description = "Enable lightweight K3s single-node cluster for cloud-native orchestration.";
      };
      role = mkOption {
        type = types.enum [ "server" "agent" ];
        default = "server";
        description = "K3s node role.";
      };
      tokenFile = mkOption {
        type = types.nullOr types.str;
        default = null;
        description = "Path to token file for K3s node join / cluster security.";
      };
    };

    gpuAcceleration = {
      enable = mkOption {
        type = types.bool;
        default = true;
        description = "Enable hardware transcoding and machine learning acceleration.";
      };
      vendor = mkOption {
        type = types.enum [ "intel" "nvidia" "amd" "none" ];
        default = "intel";
        description = "Primary GPU hardware vendor.";
      };
    };
  };

  config = mkIf cfg.enable {
    # 1. Docker Runtime Configuration
    virtualisation.docker = mkIf cfg.docker.enable {
      enable = true;
      storageDriver = cfg.docker.storageDriver;
      daemon.settings = {
        data-root = cfg.docker.dataRoot;
        log-driver = "journald";
      };
    };

    # OCI container backend compatibility
    virtualisation.oci-containers.backend = mkIf cfg.docker.enable "docker";

    # 2. K3s Runtime Configuration
    services.k3s = mkIf cfg.k3s.enable {
      enable = true;
      role = cfg.k3s.role;
      tokenFile = cfg.k3s.tokenFile;
      extraFlags = toString [
        "--disable=traefik" # We manage ingress/reverse-proxy through NaxOS
        "--snapshotter=native"
      ];
    };

    # 3. Hardware Graphics Acceleration
    hardware.graphics = mkIf cfg.gpuAcceleration.enable {
      enable = true;
      extraPackages = mkIf (cfg.gpuAcceleration.vendor == "intel") (with pkgs; [
        intel-media-driver   # Broadwell or newer
        intel-compute-runtime # OpenCL support
        vpl-gpu-rt           # QSV support (11th Gen+)
      ]);
    };

    # 4. System packages for workload operations
    environment.systemPackages = with pkgs; [
      docker-compose
      lazydocker
      kubectl
      dive
    ];
  };
}