{ lib, pkgs, ... }:

let
  NixOSRelease = "23.11";
  WAN_IFACE  = "enp0s1";
  LAN0_IFACE = "enp0s2";
  LAN1_IFACE = "enp0s3";
  LAN2_IFACE = "enp0s4";
  LAN3_IFACE = "enp0s5";
  LAN4_IFACE = "enp0s6";
in

{
  imports = [
    ./hardware-configuration.nix # generated by 'nixos-generate-config'
    ./host-specific-configuration.nix # specific to this host
  ];

  # {{ networking section }}
  networking = {
    useDHCP = false;
    nameserver = [
      "1.1.1.1"
      "1.0.0.1"
      "8.8.8.8"
      "8.8.4.4"
    ];

    vlans = {
      wan = {
        id = 10;
        interface = "${WAN_IFACE}";
      };

      pratham_lan = {
        id = 20;
        interface = "${LAN0_IFACE}";
      };
      guest_lan = {
        id = 90;
        interface = "${LAN1_IFACE}";
      };
    };

    interfaces = {
      # do not request DHCP on physical interfaces
      ${WAN_IFACE}.useDHCP  = false;
      ${LAN0_IFACE}.useDHCP = false;
      ${LAN1_IFACE}.useDHCP = false;
      ${LAN2_IFACE}.useDHCP = false;
      ${LAN3_IFACE}.useDHCP = false;
      ${LAN4_IFACE}.useDHCP = false;

      # handle VLANs now
      wan.useDHCP = false;
      lan = {
        ipv4.addresses = [{
          address = "10.0.0.1";
          prefixLength = 24;
        }];
      };
      iot = {
        ipv4.addresses = [{
          address = "10.255.255.1";
          prefixLength = 24;
        }];
      };
    };
  };

  boot.kernel.sysctl = {
    ## Z-RAM-Swap
    # Kernel docs: https://docs.kernel.org/admin-guide/sysctl/vm.html
    # Pop!_OS "docs": https://github.com/pop-os/default-settings/pull/163/files
    # Using zramswap, penalty shouldn't be that high, since if you are under
    # high memory pressure, you likeky are under high CPU load too
    # at which point, you are performing computations and latency goes moot.
    "vm.swappiness" = 180;
    # Since zramSwap.algorithm is set to 'zstd', it is recommeded to set the
    # 'vm.page-cluster' paramater to '0'.
    "vm.page-cluster" = 0;
    # Ensure that at-least 512MBytes of total memory is free to avoid system freeze.
    # Not sure about the 512MBytes value since Pop!_OS sets it to 0.01% of total memory,
    # which is roughly equal to 3.7MBytes on a 3700MBytes RPi4. The value of 512MBytes
    # also does not leave lee-way for a 512M RPi Zero.
    # A value too LOW  will result in system freeze.
    # A value too HIGH will result in OOM faster.
    "vm.min_free_kbytes"= 512000;
    # Disable 'vm.wwatermark_scale_factoratermark_boost_factor'.
    # https://groups.google.com/g/linux.debian.user/c/YcDYu-jM-to
    "vm.watermark_boost_factor" = 0;
    # Start swapping when 70% of memory is full (30% of memory is left).
    # 3000 is the MAX
    "vm.watermark_scale_factor" = 3000;
    # Increase the number of maximum mmaps a process may have (ZFS).
    # 2147483642 = 1.99-ish GiB
    "vm.max_map_count" = 2147483642;

    # The Magic SysRq key is a key combo that allows users connected to the
    # system console of a Linux kernel to perform some low-level commands.
    # Disable it, since we don't need it, and is a potential security concern.
    "kernel.sysrq" = 0;

    ## TCP hardening
    # Prevent bogus ICMP errors from filling up logs.
    "net.ipv4.icmp_ignore_bogus_error_responses" = 1;
    # Reverse path filtering causes the kernel to do source validation of
    # packets received from all interfaces. This can mitigate IP spoofing.
    "net.ipv4.conf.default.rp_filter" = 1;
    "net.ipv4.conf.all.rp_filter" = 1;
    # 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 again TIME-WAIT assassination
    "net.ipv4.tcp_rfc1337" = 1;

    ## TCP optimization
    # TCP Fast Open is a TCP extension that reduces network latency by packing
    # data in the sender’s initial TCP SYN. Setting 3 = enable TCP Fast Open for
    # both incoming and outgoing connections:
    "net.ipv4.tcp_fastopen" = 3;
    # Bufferbloat mitigations + slight improvement in throughput & latency
    "net.ipv4.tcp_congestion_control" = "bbr";
    "net.core.default_qdisc" = "cake";

    # add-ons for ze router
    "net.ipv4.conf.all.forwarding" = 1; # enable IPv4 forwarding
    "net.ipv6.conf.all.forwarding" = 1; # neable IPv6 forwarding

    # do not automatically configure any IPv6 addresses
    "net.ipv6.conf.all.accept_ra" = 0;
    "net.ipv6.conf.all.autoconf" = 0;
    "net.ipv6.conf.all.use_tempaddr" = 0;

    # allow IPv6 auto-configuration and temporary address use only on WAN
    "net.ipv6.conf.${WAN_IFACE}.accept_ra" = 2;
    "net.ipv6.conf.${WAN_IFACE}.autoconf" = 1;
  };

  # {{ packages section }}
  nixpkgs.config.allowUnfree = false; # allow non-FOSS pkgs
  environment.systemPackages = with pkgs; [
    acpi
    btop
    htop
    iperf # this is iperf3
    iproute2
    iputils
    lm_sensors
    nix-output-monitor
    nvd # diff between NixOS generations
    pciutils # provides lspci and setpci
    python3Minimal
    qemu_kvm
    ripgrep
    rsync
    tmux
    tree
    util-linux # provides blkid, losetup, lsblk, rfkill, fallocate, dmesg, etc
  ];

  programs = {
    dconf.enable = true;
    git.enable = true;
    iotop.enable = true;
    mtr.enable = true;
    neovim.enable = true;
  };

  # {{ user configuration }}
  users = {
    mutableUsers = false; # do not allow any more users on the system than what is defined here
    allowNoPasswordLogin = false;
    defaultUserShell = pkgs.bash;
    enforceIdUniqueness = true;
    users.root.hashedPassword = "$6$cxSzljtGpFNLRhx1$0HvOs4faEzUw9FYUF8ifOwBPwHsGVL7HenQMCOBNwqknBFHSlA6NIDO7U36HeQ/C9FN/B.dP.WBg3MzqQcubr0";

    users.pratham = {
      isNormalUser = true;
      description = "Pratham Patel";
      createHome = true;
      home = "/home/pratham";
      group = "pratham";
      uid = 1000;
      subUidRanges = [ { startUid = 10000; count = 65536; } ];
      subGidRanges = [ { startGid = 10000; count = 65536; } ];
      linger = true;
      hashedPassword = "$6$QLxAJcAeYARWFnnh$MaicewslNWkf/D8o6lDAWA1ECLMZLL3KWgIqPKuu/Qgt3iDBCEbEFjt3CUI4ENifvXW/blpze8IYeWhDjaKgS1";
      extraGroups = [
        "adm"
        "dialout"
        "kvm"
        "libvirt"
        "libvirtd"
        "log"
        "networkmanager"
        "rfkill"
        "sshusers"
        "sys"
        "systemd-journal"
        "wheel"
        "zfs-read"
      ];
    };
    groups.pratham = {
      name = "pratham";
      gid = 1000;
    };
  };

  # {{ sudo configuration }}
  security.sudo = {
    enable = true;
    wheelNeedsPassword = true;
  };

  # {{ system services' "parameters" go here }}
  services = {
    fwupd.enable = true;
    journald.storage = "persistent";
    logrotate.enable = true;
    timesyncd.enable = true; # NTP

    # sshd_config
    openssh = {
      enable = true;
      extraConfig = "PermitEmptyPasswords no";
      ports = [ 22 ];
      openFirewall = true;
      settings = {
        Protocol = 2;
        MaxAuthTries = 2;
        PermitEmptyPasswords = false;
        PasswordAuthentication = false;
        PermitRootLogin = "prohibit-password";
        X11Forwarding = false;
      };
    };
  };

  systemd.timers = {
    "update-nixos-config" = {
      wantedBy = [ "timers.target" ];
      timerConfig = {
        OnCalendar = "*-*-* 23:30:00";
        Unit = "update-nixos-config.service";
      };
    };
  };
  systemd.services = {
    "update-nixos-config" = {
      serviceConfig = {
        Type = "oneshot";
        User = "root";
        ExecStart = "${pkgs.coreutils}/bin/cp -fR /home/pratham/my-git-repos/pratham/prathams-nixos/nixos-configuration/. /etc/nixos";
      };
    };
  };

  # {{ configuration options related to Nix and  NixOS }}
  nix = {
    gc = {
      automatic = true;
      dates = "Sun *-*-* 00:00:00";
      options = "--delete-older-than 14d";
    };
    settings = {
      trusted-users = [ "root" "pratham" ];
      auto-optimise-store = true;
      experimental-features = [ "nix-command" "flakes" ];
    };
  };

  system = {
    stateVersion = "${NixOSRelease}";

    autoUpgrade = {
      enable = true;
      dates = "daily"; # *-*-* 00:00:00
      allowReboot = false;
      operation = "boot";
      persistent = true;
    };
  };

  # {{ misc }}
  time = {
    timeZone = "Asia/Kolkata";
    hardwareClockInLocalTime = true;
  };

  security = {
    polkit.enable = true;
    virtualisation = {
      flushL1DataCache = true;
      allowSimultaneousMultithreading = true;
    };
  };

  console = {
    enable = true;
    earlySetup = true;
  };

  # {{ environment... stuff }}
  i18n = {
    defaultLocale = "en_IN";
    extraLocaleSettings = {
      LC_ADDRESS = "en_IN";
      LC_IDENTIFICATION = "en_IN";
      LC_MEASUREMENT = "en_IN";
      LC_MONETARY = "en_IN";
      LC_NAME = "en_IN";
      LC_NUMERIC = "en_IN";
      LC_PAPER = "en_IN";
      LC_TELEPHONE = "en_IN";
      LC_TIME = "en_IN";
    };
  };

  environment = {
    homeBinInPath = true;
    localBinInPath = true;
    variables = {
      # for 'sudo -e'
      EDITOR = "nvim";
      VISUAL = "nvim";
      # systemd
      SYSTEMD_PAGER = "";
      SYSTEMD_EDITOR = "nvim";
      TERM = "xterm-256color";
      # set locale manually because even though NixOS handles the 'en_IN' locale
      # it doesn't append the string '.UTF-8' to LC_*
      # but, UTF-8 **is supported**, so just go ahead and set it manually
      LANG = lib.mkDefault "en_IN.UTF-8";
      LC_ADDRESS = lib.mkDefault "en_IN.UTF-8";
      LC_COLLATE = "en_IN.UTF-8";
      LC_CTYPE = "en_IN.UTF-8";
      LC_IDENTIFICATION = lib.mkDefault "en_IN.UTF-8";
      LC_MEASUREMENT = lib.mkDefault "en_IN.UTF-8";
      LC_MESSAGES = "en_IN.UTF-8";
      LC_MONETARY = lib.mkDefault "en_IN.UTF-8";
      LC_NAME = lib.mkDefault "en_IN.UTF-8";
      LC_NUMERIC = lib.mkDefault "en_IN.UTF-8";
      LC_PAPER = lib.mkDefault "en_IN.UTF-8";
      LC_TELEPHONE = lib.mkDefault "en_IN.UTF-8";
      LC_TIME = lib.mkDefault "en_IN.UTF-8";
      LC_ALL = "";
      # idk why, but some XDG vars aren't set, the missing ones are now set according to the
      # spec: (https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html)
      XDG_DATA_HOME = "$HOME/.local/share";
      XDG_CONFIG_HOME = "$HOME/.config";
      XDG_STATE_HOME = "$HOME/.local/state";
      XDG_CACHE_HOME = "$HOME/.cache";
    };
  };

  # yes, I want docs
  documentation = {
    enable = true;
    dev.enable = true;
    doc.enable = true;
    info.enable = true;
    man = {
      enable = true;
      generateCaches = true;
    };
  };

  # {{ virtualisation and container settings }}
  virtualisation = {
    libvirtd = {
      enable = true;
      onShutdown = "shutdown";
      allowedBridges = [ "virbr0" ]; # TODO
      qemu = {
        runAsRoot = false; # not sure about this
        verbatimConfig = ''
        user = "pratham"
        group = "pratham"
        '';
      };
    };
  };

  boot = {
    kernelParams = [
      "audit=0"
      "ignore_loglevel"

      "boot.shell_on_fail"

      "fsck.mode=auto"

      "plymouth.enable=0"
      "rd.plymouth=0"

      "no_console_suspend"
    ];
    supportedFilesystems = [
      "ext4"
      "f2fs"
      "vfat"
      "xfs"
    ];

    loader = {
      timeout = 5;
      systemd-boot = {
        enable = true;
      };
    };
  };

  hardware.enableRedistributableFirmware = true;
}