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

with lib;
let
  cfg = config.modules.security;
in {
  options.modules.security = {
    useDoas = mkEnableOption "use doas instead of sudo";
  };

  config = mkIf cfg.enable {
	boot = {
		tmp.useTmpfs = lib.mkDefault true;
		tmp.cleanOnBoot = lib.mkDefault (!config.boot.tmp.useTmpfs);
		
    	kernel.sysctl = {
    	  # magic sysrq key, allows low-level commands through keyboard input
      	  "kernel.sysrq" = 0;

          ## TCP hardening
          # prevent bogus ICMP errors from filling up logs
          "net.ipv4.icmp_ignore_bogus_error_responses" = 1;
          # do not accept IP source packets (we are not a router)
          "net.ipv4.conf.all.accept_source_route" = 0;
          "net.ipv6.conf.all.accept_source_route" = 0;
          # don't send ICMP redirects (again, we're not a router)
          "net.ipv4.conf.all.send_redirects" = 0;
          "net.ipv4.conf.default.send_redirects" = 0;
          # refuse ICMP redirects (MITM mitigations)
          "net.ipv4.conf.all.accept_redirects" = 0;
          "net.ipv4.conf.default.accept_redirects" = 0;
          "net.ipv4.conf.all.secure_redirects" = 0;
          "net.ipv4.conf.default.secure_redirects" = 0;
          "net.ipv6.conf.all.accept_redirects" = 0;
          "net.ipv6.conf.default.accept_redirects" = 0;
          # protects against SYN flood attacks
          "net.ipv4.tcp_syncookies" = 1;
          # incomplete protection against TIME-WAIT assassination
          "net.ipv4.tcp_rfc1337" = 1;

          ## TCP optimization
          # TCP fastopen
          "net.ipv4.tcp_fastopen" = 3;
          # bufferbloat mitigations + improvement in throughput and latency
          "net.ipv4.tcp_conjestion_control" = "bbr";
          "net.core.default_qdisc" = "cake";
        };
        kernelModules = [ "tcp_bbr" ];
      };

      security = {
        # prevents replacing the kernel without a reboot
      	protectKernelImage = true;
        # allows unprivileged processes to speak to privileged processes (ex. nmtui, reboot)
      	rtkit.enable = true;
        polkit.enable = true;
      };
    } // (mkIf cfg.useDoas {
    	security.sudo.enable = false;
    	security.doas.enable = true;
    	environment.systemPackages = with pkgs; [ doas-sudo-shim ];
    });
}