#!/bin/bash

set -euo pipefail

# Configuration -----------------------------------------------------------------
TARGET_SESSION_NAME="Xfce Session"
TARGET_PACKAGES=(
	xfwm4            # Compositing window manager with XFCE integration
	xfce4-session    # Provides the Xfce session entry for display managers
	xfce4-panel      # Panel with system tray support
	xfce4-settings   # Settings daemon (enables compositing toggle, theming, etc.)
	xfce4-terminal   # Handy default terminal for the new environment
)

# Utility functions --------------------------------------------------------------
info() { echo "[INFO] $*"; }
warn() { echo "[WARN] $*" >&2; }
error() { echo "[ERROR] $*" >&2; exit 1; }

require_command() {
	local cmd="$1" pkg_hint="${2:-}"
	if ! command -v "$cmd" >/dev/null 2>&1; then
		if [[ -n "$pkg_hint" ]]; then
			warn "Install '$pkg_hint' to obtain the '$cmd' command."
		fi
		error "Required command '$cmd' not found."
	fi
}

ensure_pacman() {
	require_command pacman "pacman"
	if ! grep -qi "arch" /etc/os-release 2>/dev/null; then
		warn "This script was designed for Arch Linux; continuing anyway."
	fi
}

install_packages() {
	local missing=()
	for pkg in "${TARGET_PACKAGES[@]}"; do
		if ! pacman -Qi "$pkg" >/dev/null 2>&1; then
			missing+=("$pkg")
		fi
	done

	if [[ ${#missing[@]} -eq 0 ]]; then
		info "All target packages are already installed."
		return
	fi

	if ! command -v sudo >/dev/null 2>&1; then
		error "sudo is required to install packages. Install sudo or run this script as root."
	fi

	info "Installing missing packages: ${missing[*]}"
	sudo pacman -S --needed --noconfirm "${missing[@]}"
}

print_post_install_tips() {
	cat <<EOF

------------------------------------------------------------------------
XFCE session installed.

• i3 remains your default window manager. We did not modify ~/.xinitrc,
  display manager defaults, or systemd targets.
• At your next graphical login, pick "${TARGET_SESSION_NAME}" (or "Xfce"),
  then log in to enjoy compositing via xfwm4.
• Once you are done testing Unity, simply log out and choose i3 again.

We'll log you out now so you can switch sessions safely.
------------------------------------------------------------------------
EOF
}

logout_user() {
	local session_id="${XDG_SESSION_ID:-}"

	if [[ -n "$session_id" ]] && loginctl show-session "$session_id" >/dev/null 2>&1; then
		info "Terminating current session (ID: $session_id) via loginctl."
		loginctl terminate-session "$session_id"
		return
	fi

	if loginctl list-sessions 2>/dev/null | awk '{print $1" "$3}' | grep -q " $USER$"; then
		info "Terminating all sessions for user '$USER' via loginctl."
		loginctl terminate-user "$USER"
		return
	fi

	warn "loginctl could not terminate the session; attempting fallback logout."
	pkill -KILL -u "$USER" || error "Failed to terminate user sessions. Please log out manually."
}

main() {
	ensure_pacman
	install_packages
	print_post_install_tips

	# Give the user a moment to read the instructions before logging out.
	logout_user
}

main "$@"