#!/usr/bin/env bash
#
# JbTecWiz Support Centre -- generated fix script
#
# Fault : Netplan changes do nothing, or take the network down
# Fix   : Apply safely, and recover when it goes wrong
# Source: https://jbtecwiz.com/support/lnx-net-netplan
#
# Run as     : Console access
# Expect     : 20 minutes
# Risk       : medium
# Reversible : yes
#
# WHEN THIS IS THE RIGHT FIX
#   The change took the network down -- or before making one on a remote
#   machine.
#
# HOW TO UNDO IT
#   The backup copy restores the previous state exactly.
#
# Walks the fix one step at a time and asks before each. Steps with no
# command are yours to do -- it prints those and waits. DRYRUN=1 prints
# without executing; UNATTENDED=1 does not ask.
#
# --------------------------------------------------------------------
# NO WARRANTY - USE AT YOUR OWN RISK
#
# This script is provided by JbTecWiz as-is and with no warranty of any
# kind, express or implied. You run it entirely at your own risk.
#
# JbTecWiz accepts no liability for any loss or damage arising from its
# use, including but not limited to data loss, downtime, or configuration
# changes that turn out to be wrong for your system.
#
# You are responsible for reading this script before running it, for
# satisfying yourself that it suits the machine in front of you, and for
# having a working backup first. Some steps cannot be undone.
# --------------------------------------------------------------------

set -uo pipefail
DRYRUN="${DRYRUN:-0}"
UNATTENDED="${UNATTENDED:-0}"
failed=0

rule() { printf "\n%s\n" "$(printf '-%.0s' $(seq 1 70))"; if [ $# -gt 0 ]; then echo "$1"; fi; }
prose() { echo "$1" | fold -s -w 74 | sed "s/^/  /"; }

# Returns 0 when the caller should run the command, 1 when it should not.
# A manual step always returns 1 -- there is nothing for the caller to run.
step() {  # step <n> <do> <why> <manual|cmd> [command lines...]
  local n="$1" dotext="$2" why="$3" mode="$4"; shift 4
  rule "  Step $n of 5"
  prose "$dotext"
  if [ -n "$why" ]; then echo; prose "$why"; fi
  if [ "$mode" = "manual" ]; then
    echo; echo "  -> Do this yourself, then press Enter to carry on."
    if [ "$UNATTENDED" = "0" ] && [ "$DRYRUN" = "0" ]; then read -r _; fi
    return 1
  fi
  echo; printf "    %s\n" "$@"; echo
  if [ "$DRYRUN" = "1" ]; then echo "  (dry run -- not executed)"; return 1; fi
  if [ "$UNATTENDED" = "0" ]; then
    read -r -p "  Run this step? [Y]es / [S]kip / [Q]uit " a
    case "$a" in
      [Qq]*) echo "  Stopped at your request."; exit 0 ;;
      [Ss]*) echo "  Skipped."; return 1 ;;
    esac
  fi
  return 0
}

rule
echo "  Netplan changes do nothing, or take the network down"
echo "  Apply safely, and recover when it goes wrong"
echo
echo "  Risk: medium   Reversible   20 minutes"
echo
prose 'No warranty. Use at your own risk - JbTecWiz accepts no liability. Read it before you run it, and have a backup.'
rule
echo
if [ "$UNATTENDED" = "0" ] && [ "$DRYRUN" = "0" ]; then
  read -r -p "  Ready? [y/N] " go
  case "$go" in [Yy]*) ;; *) echo "  Nothing was changed."; exit 0;; esac
fi

if step 1 'Use netplan try rather than netplan apply on any remote machine. It reverts automatically after 120 seconds unless confirmed.' 'This is the difference between a mistake that costs two minutes and one that costs a trip to the site. It exists for exactly this and almost nobody uses it.' cmd 'sudo netplan try --timeout 120'; then
  sudo netplan try --timeout 120
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 1 failed. The rest of the fix may depend on it." >&2
  fi
fi

step 2 'If you are already locked out, get to the console -- the hypervisor console, IPMI, or physical.' '' manual || true

if step 3 'Restore the backup and apply.' '' cmd 'sudo cp -a /root/netplan-backup/* /etc/netplan/' 'sudo netplan apply'; then
  sudo cp -a /root/netplan-backup/* /etc/netplan/
  sudo netplan apply
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 3 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 4 'With no backup, bring the interface up by hand to restore access while you fix the file.' '' cmd 'sudo ip addr add 192.168.1.50/24 dev ens18' 'sudo ip link set ens18 up' 'sudo ip route add default via 192.168.1.1'; then
  sudo ip addr add 192.168.1.50/24 dev ens18
  sudo ip link set ens18 up
  sudo ip route add default via 192.168.1.1
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 4 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 5 'Check the YAML for the usual errors: tabs instead of spaces, a missing colon, or an interface name that does not exist.' '' cmd 'sudo netplan generate 2>&1' 'ip -brief link show'; then
  sudo netplan generate 2>&1
  ip -brief link show
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 5 failed. The rest of the fix may depend on it." >&2
  fi
fi

rule "  Confirm it worked"
prose 'The machine is reachable and the configuration survives a reboot.'
if [ "$DRYRUN" = "0" ]; then
  sudo netplan apply && ip -brief addr
fi

rule
if [ "$failed" -gt 0 ]; then
  echo "  Finished with $failed failed step(s)."
  echo "  Read the full write-up at https://jbtecwiz.com/support/lnx-net-netplan"
else
  echo "  Finished."
fi
echo
prose 'To undo: The backup copy restores the previous state exactly.'
rule