#! /usr/bin/env bash

# Use Digital Ocean Droplet image:
#
#     Fedora 24 x64
#     Ubuntu 16.04 x64
#     Debian 8.5 x64
#
# YMMV with any other hoster + image combination.

# nixos-infect is so named because of the high likelihood of rendering a system
# inoperable. Use with caution and preferably only on newly-provisioned
# systems.
#
# WARNING NB This script wipes out the targeted host's root filesystem when it
# runs to completion. Any errors halt execution. set -x is used to help debug,
# as often a failed run leaves the system in an inconsistent state, requiring a
# rebuild (in DigitalOcean panel: Droplet Settings -> "Destroy" -> "Rebuild
# from original").
#
# TO USE:
#  - Add any custom config you want (see notes below)
#  - Deploy the droplet indicated at the top of the file, enable ipv6, add your ssh key
#  - cat customConfig.optional nixos-infect | ssh root@targethost
#
# Alternatively, use the user data mechamism by supplying the following lines (without >)
# in the Digital Ocean Web UI (or HTTP API):
#
# > #cloud-config
# >
# > runcmd:
# >   - curl https://raw.githubusercontent.com/elitak/nixos-infect/master/nixos-infect | bash 2>&1 | tee /tmp/infect.log
#
# Potential tweaks:
#  /etc/nixos/{,hardware-}configuration.nix : rudimentary mostly static config
#  /etc/nixos/networking.nix, networking settings determined at runtime
#    tweak if no ipv6, different number of adapters, etc.
#
# Motivation for this script: nixos-assimilate should supplant this script
# entirely, if it's ever completed. nixos-in-place was quite broken when I
# tried it, and also took a pretty janky approach that was substantially more
# complex than this (although it supported more platforms): it didn't install
# to root (/nixos instead), left dregs of the old filesystem (almost always
# unnecessary since starting from a fresh deployment), and most importantly,
# simply didn't work for me! (old system was being because grub wasnt properly
# reinstalled)

set -ex

export disk=$( (>/dev/null ls -l /dev/vda && echo vda) \
   || (>/dev/null ls -l /dev/sda && echo sda) ) 

makeConf() {
  # NB <<"EOF" quotes / $ ` in heredocs, <<EOF does not
  mkdir -p /etc/nixos
  local IFS=$'\n'; keys=($(grep -vE '^[[:space:]]*(#|$)' /root/.ssh/authorized_keys))
  cat > /etc/nixos/configuration.nix << EOF
{ ... }: {
  imports = [
    ./hardware-configuration.nix
    ./networking.nix # generated at runtime by nixos-infect
  ];

  boot.cleanTmpDir = true;
  networking.hostName = "$(hostname)";
  networking.firewall.allowPing = true;
  services.openssh.enable = true;
  users.users.root.openssh.authorizedKeys.keys = [$(for key in ${keys[@]}; do echo -n "
    \"$key\""; done)
  ];
}
EOF
  # (nixos-generate-config will add qemu-user and bind-mounts, so avoid)
  cat > /etc/nixos/hardware-configuration.nix << EOF
{ ... }:
{
  imports = [ <nixpkgs/nixos/modules/profiles/qemu-guest.nix> ];
  boot.loader.grub.device = "/dev/$disk";
  fileSystems."/" = { device = "/dev/${disk}1"; fsType = "ext4"; };
}
EOF

  local IFS=$'\n'
  eth0_ip4s=($(ip address show dev eth0 | grep 'inet '          | sed -r 's|.*inet ([0-9.]+)/([0-9]+).*|{ address="\1"; prefixLength=\2; }|'))
  eth0_ip6s=($(ip address show dev eth0 | grep 'inet6 .*global' | sed -r 's|.*inet6 ([0-9a-f:]+)/([0-9]+).*|{ address="\1"; prefixLength=\2; }|'))
  eth1_ip4s=($(ip address show dev eth1 | grep 'inet '          | sed -r 's|.*inet ([0-9.]+)/([0-9]+).*|{ address="\1"; prefixLength=\2; }|'))
  eth1_ip6s=($(ip address show dev eth1 | grep 'inet6 .*global' | sed -r 's|.*inet6 ([0-9a-f:]+)/([0-9]+).*|{ address="\1"; prefixLength=\2; }|'))
  gateway=($(ip route show dev eth0 | grep default | sed -r 's|default via ([0-9.]+).*|\1|'))
  gateway6=($(ip -6 route show dev eth0 | grep default | sed -r 's|default via ([0-9a-f:]+).*|\1|'))
  ether0=($(ip address show dev eth0 | grep link/ether | sed -r 's|.*link/ether ([0-9a-f:]+) .*|\1|'))
  ether1=($(ip address show dev eth1 | grep link/ether | sed -r 's|.*link/ether ([0-9a-f:]+) .*|\1|'))
  nameservers=($(grep ^nameserver /etc/resolv.conf | cut -f2 -d' '))

  cat > /etc/nixos/networking.nix << EOF
{ ... }: {
  # This file was populated at runtime with the networking
  # details gathered from the active system.
  networking = {
    nameservers = [$(for a in ${nameservers[@]}; do echo -n "
      \"$a\""; done)
    ];
    defaultGateway = "${gateway}";
    defaultGateway6 = "${gateway6}";
    interfaces = {
      eth0 = {
        ip4 = [$(for a in ${eth0_ip4s[@]}; do echo -n "
          $a"; done)
        ];
        ip6 = [$(for a in ${eth1_ip6s[@]}; do echo -n "
          $a"; done)
        ];
      };
      eth1 = {
        ip4 = [$(for a in ${eth1_ip4s[@]}; do echo -n "
          $a"; done)
        ];
        ip6 = [$(for a in ${eth1_ip6s[@]}; do echo -n "
          $a"; done)
        ];
      };
    };
  };
  services.udev.extraRules = ''
    KERNEL=="eth*", ATTR{address}=="${ether0}", NAME="eth0"
    KERNEL=="eth*", ATTR{address}=="${ether1}", NAME="eth1"
  '';
}
EOF
  #! /usr/bin/env bash
  # NB put your semi-sensitive (not posted to github) configuration in a separate
  # file and include it via this customConfig() function. e.g.:
  #  customConfig() {
  #    cat > /etc/nixos/custom.nix << EOF
  #    { config, lib, pkgs, ... }: {
  #    }
  #    EOF
  #  }
  #
  # then you can add the files in configuration.nix's imports above and run something like:
  #   cat customConfig nixos-infect | root@targethost bash
  if [[ `type -t customConfig` == "function" ]]; then customConfig; fi
}

makeSwap() {
  swapFile=`mktemp`
  dd if=/dev/zero of=$swapFile bs=1M count=$((1*1024))
  chmod 0600 $swapFile
  mkswap $swapFile
  swapon $swapFile
}

makeConf
makeSwap # smallest (512MB) droplet needs extra memory!

which dnf && dnf install -y perl-Digest-SHA # Fedora 24
which bzcat || (which yum && yum install -y bzip2) # CentOS

# DigitalOcean doesn't seem to set USER while running user data
export USER="root"
export HOME="/root"

groupadd -r nixbld -g 30000 || true
seq 1 10 | xargs -I{} useradd -c "Nix build user {}" -d /var/empty -g nixbld -G nixbld -M -N -r -s `which nologin` nixbld{} || true

curl https://nixos.org/nix/install | sh

source ~/.nix-profile/etc/profile.d/nix.sh

[ -z "$NIX_CHANNEL"] && NIX_CHANNEL="nixos-16.09"
nix-channel --remove nixpkgs
nix-channel --add "https://nixos.org/channels/$NIX_CHANNEL" nixos
nix-channel --update

export NIXOS_CONFIG=/etc/nixos/configuration.nix

nix-env --set \
  -I nixpkgs=$HOME/.nix-defexpr/channels/nixos \
  -f '<nixpkgs/nixos>' \
  -p /nix/var/nix/profiles/system \
  -A system

# Remove nix installed with curl | bash
rm -fv /nix/var/nix/profiles/default*
/nix/var/nix/profiles/system/sw/bin/nix-collect-garbage

# Follow the symlinks
[ -L /etc/resolv.conf ] && mv -v /etc/resolv.conf /etc/resolv.conf.lnk && cat /etc/resolv.conf.lnk > /etc/resolv.conf

# Staging for the Nix coup d'état
touch /etc/NIXOS
cat > /etc/NIXOS_LUSTRATE << EOF
etc/nixos
etc/resolv.conf
root/.nix-defexpr/channels
EOF

rm -rf /boot.bak && mv -v /boot /boot.bak &&
  /nix/var/nix/profiles/system/bin/switch-to-configuration boot

reboot