# vim: ts=2
{
  config,
  lib,
  ...
}:
with lib; let
  cfg = config.system.fileSystemLayouts;
  defaultMountOptions = [
    "compress-force=zstd:15" # This saves disk space, at a performance cost
    "noatime" # should have some performance upsides, and I don't use it anyways
    "lazytime" # make time changes in memory
  ];
in {
  options.system.fileSystemLayouts = {
    enable = mkEnableOption (mdDoc "fileSystemLayout");
    mainDisk = mkOption {
      type = lib.types.path;
      example = literalExpression "/dev/disk/by-uuid/0442cb6d-f13a-4635-b487-fa76189774c5";
      description = lib.mdDoc "Path to the main disk";
    };
    efiDisk = mkOption {
      type = lib.types.path;
      example = literalExpression "/dev/disk/by-uuid/5143-6136";
      description = lib.mdDoc "Path to the main disk";
    };
    ssd = mkOption {
      type = lib.types.bool;
      example = literalExpression "true";
      default = false;
      description = lib.mdDoc "Enable ssd specific improvements?";
    };
    swap = {
      uuid = mkOption {
        type = lib.types.str;
        example = literalExpression "d1d20ae7-3d8a-44da-86da-677dbbb10c89";
        description = lib.mdDoc "The uuid of the swapfile";
      };
      resumeOffset = mkOption {
        type = lib.types.str;
        example = literalExpression "134324224";
        description = lib.mdDoc "The resume offset of the swapfile";
      };
    };
  };

  config = mkIf cfg.enable {
    systemd = mkIf cfg.ssd {
      timers.fstrim = {
        wantedBy = ["timers.target"];
        wants = ["fstrim.service"];
        unitConfig = {
          Description = "Discard unused blocks once a week";
          Documentation = "man:fstrim";
          ConditionVirtualization = "!container";
          ConditionPathExists = "!/etc/initrd-release";
        };
        timerConfig = {
          OnCalendar = "weekly";
          AccuracySec = "1h";
          Persistent = "true";
          RandomizedDelaySec = "6000";
        };
      };
      services.fstrim = {
        unitConfig = {
          Description = "Discard unused blocks on filesystems from /etc/fstab";
          Documentation = "man:fstrim(8)";
          ConditionVirtualization = "!container";
        };
        serviceConfig = {
          Type = "oneshot";
          ExecStart = "/usr/bin/fstrim --listed-in /etc/fstab:/proc/self/mountinfo --verbose --quiet-unsupported";
          PrivateDevices = "no";
          PrivateNetwork = "yes";
          PrivateUsers = "no";
          ProtectKernelTunables = "yes";
          ProtectKernelModules = "yes";
          ProtectControlGroups = "yes";
          MemoryDenyWriteExecute = "yes";
          SystemCallFilter = "@default @file-system @basic-io @system-service";
        };
      };
    };

    fileSystems = {
      "/" = {
        device = "none";
        fsType = "tmpfs";
        options = ["defaults" "size=4G" "mode=755"];
      };
      "/nix" = {
        device = cfg.mainDisk;
        fsType = "btrfs";
        options = ["subvol=nix-store"] ++ defaultMountOptions;
      };
      "/srv" = {
        device = cfg.mainDisk;
        fsType = "btrfs";
        neededForBoot = true;
        options = ["subvol=persistent-storage"] ++ defaultMountOptions;
      };
      "/swap" = {
        device = cfg.mainDisk;
        fsType = "btrfs";
        neededForBoot = true;
        options = ["subvol=swap"] ++ defaultMountOptions;
      };
      "/boot" = {
        device = cfg.efiDisk;
        fsType = "vfat";
      };
    };
    swapDevices = [
      {
        device = "/swap/swapfile";
        discardPolicy = "both"; # TODO this is the default in swapon, so it should be fine?
        priority = 1; # should not be used, aside of hibernate
      }
    ];
    zramSwap = {
      enable = true;
      priority = 10; # needs to be higher than harware-swap
    };
    boot.kernelParams = [
      "resume=UUID=${cfg.swap.uuid}"
      "resume_offset=${cfg.swap.resumeOffset}"
    ];
  };
}