# What CachyOS adds on top of plain Arch: its kernel and the cachyos-settings
# package (sysctl, udev rules, systemd defaults), ported file by file. The CachyOS
# file each part comes from is named next to it, so they can be compared when
# CachyOS changes something.
#
# Not ported, because it does nothing on this machine: the laptop audio power
# saving and touchpad rules, the old-Radeon (SI/CIK) amdgpu options, and
# debuginfod. Snapper root snapshots are replaced by NixOS generations: every
# rebuild is a boot menu entry you can go back to.
{
  inputs,
  lib,
  pkgs,
  ...
}:
let
  # cachyos-settings: /usr/bin/game-performance. Runs a game with the
  # "performance" power profile held, and the screensaver inhibited. Use it as
  # a Steam launch option: game-performance %command%
  game-performance = pkgs.writeShellApplication {
    name = "game-performance";
    runtimeInputs = [ pkgs.power-profiles-daemon pkgs.systemd ];
    text = ''
      if ! powerprofilesctl list | grep -q 'performance:'; then
        exec "$@"
      fi
      if [ -n "''${GAME_PERFORMANCE_SCREENSAVER_ON:-}" ]; then
        exec powerprofilesctl launch -p performance \
          -r "Launched with CachyOS game-performance utility" -- "$@"
      else
        exec systemd-inhibit --why "CachyOS game-performance is running" powerprofilesctl launch \
          -p performance -r "Launched with CachyOS game-performance utility" -- "$@"
      fi
    '';
  };

  # cachyos-settings: /usr/bin/dlss-swapper. Steam launch option:
  # dlss-swapper %command%
  dlss-swapper = pkgs.writeShellScriptBin "dlss-swapper" ''
    export PROTON_ENABLE_NGX_UPDATER=1
    export DXVK_NVAPI_DRS_NGX_DLSS_RR_OVERRIDE=on
    export DXVK_NVAPI_DRS_NGX_DLSS_SR_OVERRIDE=on
    export DXVK_NVAPI_DRS_NGX_DLSS_FG_OVERRIDE=on
    export DXVK_NVAPI_DRS_NGX_DLSS_RR_OVERRIDE_RENDER_PRESET_SELECTION=render_preset_latest
    export DXVK_NVAPI_DRS_NGX_DLSS_SR_OVERRIDE_RENDER_PRESET_SELECTION=render_preset_latest
    exec "$@"
  '';
in
{
  # --- Kernel ----------------------------------------------------------------

  # The overlay pins the kernel to the nixpkgs it was built with, so the build
  # doesn't change with this system's nixpkgs.
  nixpkgs.overlays = [ inputs.nix-cachyos-kernel.overlays.pinned ];

  # git.granstrm.com builds the kernel, its modules and the NVIDIA driver every
  # night the kernel changes (flake.nix's `ci`), and serves them from its
  # binary cache.
  nix.settings = {
    substituters = [ "https://cache.git.granstrm.com" ];
    trusted-public-keys = [ "cache.git.granstrm.com-1:Y6BjEJMQZ02kt2oOJ/99RU+NTDZDsBY8tqIiypq1ong=" ];
  };

  # Same build as linux-cachyos on CachyOS's znver4 repo: EEVDF scheduler,
  # 1000 Hz, full preemption, Clang ThinLTO, tuned for Zen 4 (also right for
  # this Zen 5 CPU, as on CachyOS).
  boot.kernelPackages = pkgs.cachyosKernels.linuxPackages-cachyos-latest-lto-zen4;

  boot.kernelParams = [
    "nowatchdog"
    # cachyos-settings: udev/rules.d/30-zram.rules turns zswap off once zram is
    # up; it is always up here, so it is simply off from boot.
    "zswap.enabled=0"
  ];

  # modprobe.d/blacklist.conf
  boot.blacklistedKernelModules = [
    "iTCO_wdt"
    "sp5100_tco"
  ];

  # modules-load.d/ntsync.conf: Wine/Proton's NT synchronization primitives.
  boot.kernelModules = [ "ntsync" ];

  boot.extraModprobeConfig = ''
    # modprobe.d/nvidia.conf
    options nvidia NVreg_InitializeSystemMemoryAllocations=0
    # cachyos-iw-set-regdomain: the Wi-Fi regulatory domain, from the time zone.
    options cfg80211 ieee80211_regdom="NO"
  '';

  # --- sysctl.d/70-cachyos-settings.conf --------------------------------------

  boot.kernel.sysctl = {
    # 150 rather than the file's 100: 30-zram.rules raises it to 150 as soon as
    # zram is active, which on CachyOS is always.
    "vm.swappiness" = 150;
    "vm.vfs_cache_pressure" = 50;
    "vm.dirty_bytes" = 268435456;
    "vm.page-cluster" = 0;
    "vm.dirty_background_bytes" = 67108864;
    "vm.dirty_writeback_centisecs" = 1500;
    "kernel.nmi_watchdog" = 0;
    "kernel.unprivileged_userns_clone" = 1;
    "kernel.printk" = "3 3 3 3";
    "kernel.kptr_restrict" = 2;
    "net.core.netdev_max_backlog" = 4096;
    "fs.file-max" = 2097152;
  };

  # --- udev rules ---------------------------------------------------------------

  services.udev.extraRules = ''
    # 60-ioschedulers.rules
    ACTION=="add|change", KERNEL=="sd[a-z]*", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="bfq"
    ACTION=="add|change", KERNEL=="sd[a-z]*|mmcblk[0-9]*", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="mq-deadline"
    ACTION=="add|change", KERNEL=="nvme[0-9]*", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="kyber"

    # 40-hpet-permissions.rules, 99-cpu-dma-latency.rules
    KERNEL=="rtc0", GROUP="audio"
    KERNEL=="hpet", GROUP="audio"
    DEVPATH=="/devices/virtual/misc/cpu_dma_latency", OWNER="root", GROUP="audio", MODE="0660"

    # 50-sata.rules
    ACTION=="add", SUBSYSTEM=="scsi_host", KERNEL=="host*", ATTR{link_power_management_supported}=="1", ATTR{link_power_management_policy}=="*", ATTR{link_power_management_policy}="max_performance"

    # 71-nvidia.rules: runtime power management for the NVIDIA GPU.
    ACTION=="add|bind", SUBSYSTEM=="pci", DRIVERS=="nvidia", ATTR{vendor}=="0x10de", ATTR{class}=="0x03[0-9]*", TEST=="power/control", ATTR{power/control}="auto"
    ACTION=="remove|unbind", SUBSYSTEM=="pci", DRIVERS=="nvidia", ATTR{vendor}=="0x10de", ATTR{class}=="0x03[0-9]*", TEST=="power/control", ATTR{power/control}="on"
  '';

  # --- tmpfiles.d ---------------------------------------------------------------

  systemd.tmpfiles.rules = [
    # thp.conf, thp-shrinker.conf
    "w! /sys/kernel/mm/transparent_hugepage/defrag - - - - defer+madvise"
    "w! /sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none - - - - 409"
    # coredump.conf
    "e /var/lib/systemd/coredump - - - 3d"
  ];

  # --- systemd ------------------------------------------------------------------

  # system.conf.d/00-timeout.conf, 10-limits.conf
  systemd.settings.Manager = {
    DefaultTimeoutStartSec = "15s";
    DefaultTimeoutStopSec = "10s";
    DefaultLimitNOFILE = "2048:2097152";
  };
  # user.conf.d/00-timeout.conf, 10-limits.conf
  systemd.user.settings.Manager = {
    DefaultTimeoutStartSec = "15s";
    DefaultTimeoutStopSec = "10s";
    DefaultLimitNOFILE = "1024:1048576";
  };

  # journald.conf.d/00-journal-size.conf
  services.journald.settings.Journal.SystemMaxUse = "50M";

  # timesyncd.conf.d/10-timesyncd.conf
  services.timesyncd = {
    servers = [ "time.cloudflare.com" ];
    fallbackServers = [
      "time.google.com"
      "0.nixos.pool.ntp.org"
      "1.nixos.pool.ntp.org"
    ];
  };

  # system/user@.service.d/delegate.conf: lets user services (and ananicy)
  # manage their own CPU, I/O and memory controllers.
  systemd.services."user@".serviceConfig.Delegate = "cpu cpuset io memory pids";

  # system/rtkit-daemon.service.d/override.conf
  security.rtkit.enable = true;
  systemd.services.rtkit-daemon.serviceConfig.LogLevelMax = "info";

  # systemd-oomd per-slice defaults (system.slice.d, user-.slice.d,
  # session.slice.d).
  systemd.oomd.enable = true;
  systemd.slices = {
    "system".sliceConfig = {
      ManagedOOMSwap = "kill";
      ManagedOOMMemoryPressure = "kill";
      ManagedOOMMemoryPressureLimit = "80%";
    };
    "user-".sliceConfig = {
      ManagedOOMSwap = "kill";
      ManagedOOMMemoryPressure = "kill";
      ManagedOOMMemoryPressureLimit = "80%";
    };
  };
  systemd.user.slices.session.sliceConfig.ManagedOOMPreference = "omit";

  # system/pci-latency.service + /usr/bin/pci-latency
  systemd.services.pci-latency = {
    description = "Adjust latency timers for PCI peripherals";
    wantedBy = [ "multi-user.target" ];
    serviceConfig.Type = "oneshot";
    path = [ pkgs.pciutils ];
    script = ''
      setpci -v -s '*:*' latency_timer=20
      setpci -v -s '0:0' latency_timer=0
      setpci -v -d "*:*:04xx" latency_timer=80
    '';
  };

  # security/limits.d/20-audio.conf
  security.pam.loginLimits = [
    {
      domain = "@audio";
      item = "rtprio";
      type = "-";
      value = "99";
    }
    {
      domain = "@audio";
      item = "nice";
      type = "-";
      value = "-11";
    }
  ];

  hardware.wirelessRegulatoryDatabase = true;

  # --- CachyOS services ---------------------------------------------------------

  # ananicy-cpp with CachyOS's rules: renices games, compilers, browsers etc.
  services.ananicy = {
    enable = true;
    package = pkgs.ananicy-cpp;
    rulesProvider = pkgs.ananicy-rules-cachyos;
  };

  # bpftune: auto-tunes network and other kernel settings (enabled on CachyOS).
  services.bpftune.enable = true;

  # sched-ext schedulers, as CachyOS's scx-scheds. Off there too (scx_loader was
  # disabled); to try one:
  # services.scx = { enable = true; scheduler = "scx_lavd"; };

  # power-profiles-daemon, with the profile you had set on CachyOS.
  services.power-profiles-daemon.enable = true;
  # Started with the daemon itself (wanting it from multi-user.target makes an
  # ordering cycle). Skipped where there is no performance profile, e.g. in a VM.
  systemd.services.power-profile-performance = {
    description = "Select the performance power profile";
    after = [ "power-profiles-daemon.service" ];
    bindsTo = [ "power-profiles-daemon.service" ];
    wantedBy = [ "power-profiles-daemon.service" ];
    serviceConfig.Type = "oneshot";
    path = [ pkgs.power-profiles-daemon ];
    script = ''
      if powerprofilesctl list | grep -q 'performance:'; then
        powerprofilesctl set performance
      fi
    '';
  };

  environment.systemPackages = [
    game-performance
    dlss-swapper
  ];
}