#!/bin/bash
#
# Purpose : Check the machine before install.sh sets it up, and offer to fix
#           what can be fixed: too little disk space, / not on btrfs, a login
#           screen other than GNOME's GDM, PulseAudio instead of PipeWire.
#           Exits 1 to stop the install. refresh runs install.sh again, so it
#           says nothing on a machine where all is well.

COREDESKTOP="$HOME/.local/share/coredesktop"
source "$COREDESKTOP/utils.sh"

SERVICES_OFF="$HOME/.config/coredesktop/services-off"

# install.sh is usually piped into bash, so ask on the terminal
TTY="${COREDESKTOP_TTY:-/dev/tty}"

# ask <question> <default y|n> <answer without a terminal y|n>
ask() {
  local answer
  if ! { : < "$TTY"; } 2> /dev/null; then
    [ "$3" = y ]
    return
  fi
  if [ "$2" = y ]; then
    read -rp "$1 [Y/n] " answer < "$TTY"
    [[ "$answer" != [nN]* ]]
  else
    read -rp "$1 [y/N] " answer < "$TTY"
    [[ "$answer" == [yY]* ]]
  fi
}

# Set up before: install.sh records migrations as its last step
already_installed() {
  [ -d "$HOME/.local/state/coredesktop/migrations" ]
}

check_disk() {
  local need=60 free
  already_installed && need=10
  free="$(df -k --output=avail / | tail -n 1 | tr -d ' ')"
  [[ "$free" =~ ^[0-9]+$ ]] || return 0
  free=$(( free / 1024 / 1024 ))
  (( free < need )) || return 0
  echo "Only $free GB is free on /, and this needs about $need GB."
  ask "Continue anyway?" n n
}

# Can't be fixed without reinstalling Arch, so only asked about the first time
check_btrfs() {
  local fstype
  already_installed && return 0
  fstype="$(findmnt -no FSTYPE /)"
  [ "$fstype" = btrfs ] && return 0
  echo "/ is on $fstype, not btrfs, so update can't take a snapshot first, and a bad"
  echo "update can't be rolled back (see Snapshots in the README). Only reinstalling Arch"
  echo "with btrfs, archinstall's default, changes that."
  ask "Continue without snapshots?" y y
}

# CoreDesktop turns on GDM, which fails while another login screen is on
check_display_manager() {
  local dm
  dm="$(readlink /etc/systemd/system/display-manager.service 2> /dev/null)"
  dm="$(basename "${dm:-none}")"
  [ "$dm" = none ] || [ "$dm" = gdm.service ] && return 0
  grep -qsx "system gdm.service" "$SERVICES_OFF" && return 0

  echo "This machine's login screen is ${dm%.service}, not GNOME's (GDM)."
  if ask "Switch to GNOME's login screen? It takes over when you restart." y n; then
    # enable_services turns GDM on later in the install
    sudo systemctl disable "$dm" || return 1
  else
    mkdir -p "$(dirname "$SERVICES_OFF")"
    echo "system gdm.service" >> "$SERVICES_OFF"
    echo "Keeping ${dm%.service}. Choose GNOME from its session menu when you log in."
    echo "To switch later: sudo systemctl disable $dm && sudo systemctl enable gdm"
    echo "then delete the line \"system gdm.service\" from $SERVICES_OFF"
  fi
}

# PipeWire replaces PulseAudio; GNOME's screen sharing needs it, and calls in
# Jitsi and Element work best with it
check_sound() {
  local plugins=()
  is_installed pulseaudio || return 0

  echo "This machine plays sound through PulseAudio. PipeWire replaces it: GNOME's"
  echo "screen sharing needs it, and calls in Jitsi and Element work best with it."
  if ! ask "Switch to PipeWire?" y n; then
    echo "Keeping PulseAudio."
    return 0
  fi
  # Its modules (bluetooth, ...) need it, so they go first; PipeWire does
  # what they did
  mapfile -t plugins < <(pacman -Qq | grep '^pulseaudio-')
  if (( ${#plugins[@]} > 0 )); then
    sudo pacman -R --noconfirm "${plugins[@]}" || return 1
  fi
  # --ask=4 answers yes to removing pulseaudio, which pipewire-pulse replaces
  sudo pacman -S --needed --noconfirm --ask=4 pipewire pipewire-pulse pipewire-alsa wireplumber || return 1
  echo "Switched to PipeWire. It takes over when you log out and in again."
}

check_disk || exit 1
check_btrfs || exit 1
check_display_manager || exit 1
check_sound || exit 1
exit 0