#!/bin/bash
# switch-wm — choose which window manager lightdm boots you into.
# Flips the autologin + default session between i3 and dwm in both lightdm
# config files (main lightdm.conf overrides the conf.d drop-in, so keep both in
# sync). Reboot or log out to apply.
#   switch-wm        show the current boot session
#   switch-wm dwm    boot into dwm next time
#   switch-wm i3     boot into i3 next time
# Recovery: if a session misbehaves at boot, go to a TTY (Ctrl+Alt+F3),
# log in, run `switch-wm i3`, then `reboot`.
set -euo pipefail

readonly CONFS=(
    /etc/lightdm/lightdm.conf
    /etc/lightdm/lightdm.conf.d/50-autologin.conf
)

show_current() {
    grep -hE '^autologin-session=' /etc/lightdm/lightdm.conf 2>/dev/null \
        | tail -1 | cut -d= -f2
}

target="${1:-}"
case "$target" in
    "")     echo "boot session: $(show_current)"; exit 0 ;;
    i3|dwm) ;;
    *)      echo "Usage: $(basename "$0") {i3|dwm}   (no arg = show current)" >&2; exit 1 ;;
esac

if [[ ! -f "/usr/share/xsessions/${target}.desktop" ]]; then
    echo "Error: /usr/share/xsessions/${target}.desktop not found — is '${target}' installed?" >&2
    exit 1
fi

for f in "${CONFS[@]}"; do
    [[ -f "$f" ]] || continue
    sudo sed -i -E \
        "s/^(autologin-session=).*/\1${target}/; s/^(user-session=).*/\1${target}/" "$f"
done

echo "Boot session set to '${target}'. Reboot (or log out) to apply."