nixos/hardware/filesystem.nix

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

let
rootDisk = "/dev/disk/by-partlabel/disk-${hostname}-root";
bootDisk = "/dev/disk/by-partlabel/disk-${hostname}-ESP";
in

{
    boot.initrd.postDeviceCommands = lib.mkAfter ''
        mkdir /btrfs_tmp
        mount ${rootDisk} /btrfs_tmp
        if [[ -e /btrfs_tmp/root ]]; then
            mkdir -p /btrfs_tmp/old_roots
            timestamp=$(date +%Y-%m-%d_%H-%M-%S)
            mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$timestamp"
        fi

        delete_subvolume_recursively() {
            IFS=$'\n'
            for i in $(btrfs subvolume list -o "$1" | cut -f 9 -d ' '); do
                delete_subvolume_recursively "/btrfs_tmp/$i"
            done
            btrfs subvolume delete "$1"
        }

        for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +7); do
            delete_subvolume_recursively "$i"
        done

        btrfs subvolume create /btrfs_tmp/root
        umount /btrfs_tmp
    '';

    fileSystems."/" = {
        device = rootDisk;
        fsType = "btrfs";
        options = [ "subvol=root" ];
    };

    fileSystems."/persist" = {
        device = rootDisk;
        neededForBoot = true;
        fsType = "btrfs";
        options = [ "subvol=persist" ];
    };

    fileSystems."/nix" = {
        device = rootDisk;
        neededForBoot = true;
        fsType = "btrfs";
        options = [ "subvol=nix" ];
    };

    fileSystems."/boot" = {
        device = bootDisk;
        fsType = "vfat";
        options = [ "fmask=0022" "dmask=0022" "umask=0077" ];
    };

    swapDevices = [ {
        device = "/.swapvol/swapfile";
    } ];
}