#!/usr/bin/env bash
#
# A simple bash script to replicate essential "timedatectl" functionality:
# - Show current time and time zone
# - List available time zones
# - Set time or time zone
# - Enable/disable/verify NTP
# - Configure RTC as localtime or UTC

# ------------------------------------------------------------------------------
# Utility functions
# ------------------------------------------------------------------------------

print_usage() {
	cat <<EOF
Usage: $(basename "$0") COMMAND [ARGS...]

Commands:
  status                Show current time/date, timezone, RTC mode, NTP status
  set-time [TIME]       Set system clock to TIME (e.g. "2025-03-21 18:00:00")
  set-timezone [ZONE]   Set system timezone to ZONE (Region/City)
  list-timezones        List all known timezones in /usr/share/zoneinfo
  set-local-rtc [0|1]   Set whether RTC is in local time (1) or UTC (0)
  set-ntp [true|false]  Enable or disable systemd-timesyncd (if available)

Examples:
  $(basename "$0") status
  $(basename "$0") set-time "2025-03-21 18:00:00"
  $(basename "$0") set-timezone America/New_York
  $(basename "$0") set-local-rtc 1
  $(basename "$0") set-ntp true

Note: Most operations require root privileges. Use sudo if necessary.
EOF
}

# Safely exit on errors
abort() {
	echo "Error: $*" >&2
	exit 1
}

# ------------------------------------------------------------------------------
# Functions for each major operation
# ------------------------------------------------------------------------------

show_status() {
	echo "=== System Time/Date ==="
	date

	echo
	echo "=== Time Zone ==="
	# Attempt to parse the symlink at /etc/localtime
	# On many systems, /etc/localtime is a symlink to /usr/share/zoneinfo/Region/City
	if [ -L /etc/localtime ]; then
		local tz_target
		tz_target=$(readlink -f /etc/localtime)
		# Remove the /usr/share/zoneinfo/ part to display just Region/City
		local tz_name
		tz_name="${tz_target#/usr/share/zoneinfo/}"
		echo "Time zone: $tz_name"
	else
		# Some distros have /etc/localtime as a copy of the zone file
		# Try to read /etc/timezone as a fallback (Debian-based)
		if [ -f /etc/timezone ]; then
			echo "Time zone: $(cat /etc/timezone)"
		else
			echo "Time zone: Unknown (not a symlink, and /etc/timezone missing)"
		fi
	fi

	echo
	echo "=== RTC in local TZ? ==="
	# If /etc/adjtime exists and the last line is "LOCAL", that typically indicates localtime
	# If it’s "UTC" or absent, the RTC is typically in UTC.
	if [ -f /etc/adjtime ]; then
		local rtc_mode
		rtc_mode=$(tail -n 1 /etc/adjtime)
		if [ "$rtc_mode" = "LOCAL" ]; then
			echo "RTC is in local time."
		else
			echo "RTC is in UTC."
		fi
	else
		echo "Cannot determine RTC mode (no /etc/adjtime)."
	fi

	echo
	echo "=== NTP Service Status ==="
	# Attempt to detect if systemd-timesyncd is enabled/active
	if command -v systemctl &>/dev/null; then
		if systemctl is-enabled systemd-timesyncd &>/dev/null; then
			echo "systemd-timesyncd service is enabled."
		else
			echo "systemd-timesyncd service is disabled."
		fi

		if systemctl is-active systemd-timesyncd &>/dev/null; then
			echo "systemd-timesyncd service is active (running)."
		else
			echo "systemd-timesyncd service is not running."
		fi
	else
		echo "systemctl is not available. Cannot determine NTP status this way."
	fi

	echo
}

set_time() {
	local new_time="$1"

	if [ -z "$new_time" ]; then
		abort "Please specify a time, e.g. '2025-03-21 18:00:00'"
	fi

	echo "Setting system time to: $new_time"
	# Using 'date' to set system time.
	# Format can be e.g. "YYYY-MM-DD HH:MM:SS"
	# Usually you need root privileges for this:
	if ! date -s "$new_time"; then
		abort "Failed to set system time. Check your permissions?"
	fi

	# Also sync to hardware clock:
	if command -v hwclock &>/dev/null; then
		hwclock --systohc || echo "Warning: couldn't sync with HW clock."
	fi
}

list_timezones() {
	local zoneinfo_dir="/usr/share/zoneinfo"
	if [ ! -d "$zoneinfo_dir" ]; then
		abort "Cannot find $zoneinfo_dir directory."
	fi

	echo "List of available time zones (under $zoneinfo_dir):"
	# We filter out possible files that are not real zone data.
	# On some systems, zone data might be in subdirectories (Region/City).
	find "$zoneinfo_dir" -type f | sed "s|^$zoneinfo_dir/||"
}

set_timezone() {
	local tz="$1"

	if [ -z "$tz" ]; then
		abort "Please specify a time zone, e.g. 'America/New_York'"
	fi

	local zoneinfo_file="/usr/share/zoneinfo/$tz"
	if [ ! -f "$zoneinfo_file" ]; then
		abort "Time zone '$tz' not found under /usr/share/zoneinfo"
	fi

	echo "Linking /etc/localtime to $zoneinfo_file"
	ln -sf "$zoneinfo_file" /etc/localtime || abort "Failed to link /etc/localtime"

	# Some distros use /etc/timezone to store the name of the current timezone
	if [ -w /etc/timezone ]; then
		echo "$tz" >/etc/timezone
	fi

	echo "Time zone changed to $tz."
}

set_local_rtc() {
	local is_local="$1"

	if [ -z "$is_local" ]; then
		abort "Please specify 0 or 1. Example: set-local-rtc 1"
	fi

	# We update /etc/adjtime accordingly:
	# - If local time: last line should be LOCAL
	# - If UTC: last line should be UTC
	# We also update the hardware clock accordingly.
	if [ "$is_local" = "1" ]; then
		echo "Configuring RTC to use local time."
		# "hwclock --localtime" is fairly ambiguous (it sets hardware clock from system time).
		# We use the below approach:
		hwclock --systohc --localtime || echo "Warning: couldn't set HW clock localtime."
		# Overwrite /etc/adjtime fully:
		cat <<EOF >/etc/adjtime
0.0 0 0.0
0
LOCAL
EOF
	else
		echo "Configuring RTC to use UTC."
		hwclock --systohc --utc || echo "Warning: couldn't set HW clock to UTC."
		cat <<EOF >/etc/adjtime
0.0 0 0.0
0
UTC
EOF
	fi
}

set_ntp() {
	local enable_ntp="$1"
	if ! command -v systemctl &>/dev/null; then
		echo "systemctl not available. Cannot manage systemd-timesyncd. Exiting."
		return 1
	fi

	# systemd-timesyncd is the typical built-in NTP client for systemd-based systems
	case "$enable_ntp" in
	true | True | 1 | on)
		echo "Enabling and starting systemd-timesyncd..."
		systemctl enable systemd-timesyncd || echo "Failed to enable timesyncd."
		systemctl start systemd-timesyncd || echo "Failed to start timesyncd."
		;;
	false | False | 0 | off)
		echo "Disabling and stopping systemd-timesyncd..."
		systemctl disable systemd-timesyncd || echo "Failed to disable timesyncd."
		systemctl stop systemd-timesyncd || echo "Failed to stop timesyncd."
		;;
	*)
		abort "Unknown argument '$enable_ntp'. Use 'true' or 'false'."
		;;
	esac
}

# ------------------------------------------------------------------------------
# Main
# ------------------------------------------------------------------------------

main() {
	local cmd="$1"
	shift || true

	case "$cmd" in
	status)
		show_status
		;;
	set-time)
		set_time "$@"
		;;
	set-timezone)
		set_timezone "$@"
		;;
	list-timezones)
		list_timezones
		;;
	set-local-rtc)
		set_local_rtc "$@"
		;;
	set-ntp)
		set_ntp "$@"
		;;
	"" | help | --help | -h)
		print_usage
		;;
	*)
		echo "Unknown command: $cmd"
		print_usage
		exit 1
		;;
	esac
}

if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
	if [ $# -lt 1 ]; then
		print_usage
		exit 0
	fi
	main "$@"
fi