#!/bin/sh
set -eu


usage() {
	cat <<-'EOF'
		Usage:
		  vm [-G] [-n] [-S] [-v] ACTION [OS [-- QEMU_OPTIONS...]]
		  vm -h
	EOF
}

help() {
	cat <<-'EOF'


		Options:
		  -G              use graphics
		  -n              dry-run: don't execute any code, assumes -v
		  -S              don't write to VM image (snapshot on)
		  -v              verbose mode
		  -h, --help      show this message

		  ACTION          one of:
		                  - up
		                  - down
		                  - status
		  OS              the name of the OS to be acted upon
		  QEMU_OPTIONS    command line options to be given verbatim to QEMU


		Manage the state of known virtual machines.

		The VM QCOW2 images are stored under
		$XDG_STATE_HOME/vm/qemu/, as "$OS.qcow2" files.  The PIDs
		of the running images are stored in individual files under
		$XDG_RUNTIME_DIR/vm/pids/, as "$OS.pid" files.

		It also generates an SSH configuration file under
                $XDG_DATA_HOME/vm/ssh.conf to be `Included` by the main
                ~/.ssh/config file, which contains one alias entry for each VM,
                so that one can do a combination of `vm up alpine && ssh alpine`.


		Examples:

		  Start the VM for Alpine:

		    $ vm up alpine


		  Stop the VM for Slackware, which was already down

		    $ vm down slackware
		    The VM for "slackware" is not running, already.


		  List the available VMs, and their current state:

		    $ vm status
		    alpine up
		    slackware down
		    freebsd:up
	EOF
}


for flag in "$@"; do
	case "$flag" in
		--)
			break
			;;
		--help)
			usage
			help
			exit
			;;
		*)
			;;
	esac
done

DRY_RUN=false
GRAPHICS=false
SNAPSHOT=false
VERBOSE=false
while getopts 'GnSvh' flag; do
	case "$flag" in
		G)
			GRAPHICS=true
			;;
		n)
			DRY_RUN=true
			VERBOSE=true
			;;
		S)
			SNAPSHOT=true
			;;
		v)
			VERBOSE=true
			;;
		h)
			usage
			help
			exit
			;;
		*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))



QCOW_DIR="${XDG_STATE_HOME:-$HOME/.local/state}"/vm/qemu
RUNDIR="${XDG_RUNTIME_DIR:-${TMPDIR:-/tmp}}/vm"
LOGS="$RUNDIR"/logs
mkdir -p "$RUNDIR" "$QCOW_DIR" "$XDG_DATA_HOME"/vm

guess_name() {
	PREFIX="$1"
	IMAGES="$(find "$QCOW_DIR" -type f -name "${PREFIX}*")"
	COUNT="$(echo "$IMAGES" | wc -l)"
	if [ "$COUNT" != 1 ]; then
		printf 'Cannot guess name with the given prefix: "%s".\n' "$PREFIX" >&2
		printf '\nThe possibilities are:\n' >&2
		printf '%s\n' "$IMAGES" |
			xargs -I% basename % .qcow2 |
			sed 's/^/- /' >&2
		exit 2
	fi
	printf '%s\n' "$(basename "$IMAGES" .qcow2)"
}

write_ssh_config() {
	for port in "$RUNDIR"/*.port; do
		if [ ! -e "$port" ]; then
			break
		fi
		NAME="$(basename "$port" .port)"
		PORT="$(cat "$port")"
		cat <<-EOF
			Host $NAME
			  HostName localhost
			  Port $PORT

		EOF
	done > "$XDG_DATA_HOME"/vm/ssh.conf
}

write_ssh_config


ACTION="${1:-}"
OS="${2:-}"

eval "$(assert-arg "$ACTION" 'ACTION')"
shift


FLAGS=''
if [ "$GRAPHICS" = false ]; then
	FLAGS="$FLAGS -nographic"
else
	FLAGS="$FLAGS -display sdl"
fi
if [ "$SNAPSHOT" = true ]; then
	FLAGS="$FLAGS -snapshot"
fi


case "$ACTION" in
	status)
		for img in "$QCOW_DIR"/*.qcow2; do
			if [ ! -e "$img" ]; then
				break
			fi
			NAME="$(basename "$img" .qcow2)"
			if [ -e "$RUNDIR/$NAME.pid" ]; then
				STATUS=up
			else
				STATUS=down
			fi
			printf '%s\t%s\n' "$NAME" "$STATUS"
		done
		;;
	up)
		eval "$(assert-arg "$OS" 'OS')"
		shift
		if [ "${1:-}" = '--' ]; then
			shift
		fi

		OS="$(guess_name "$OS")"
		PID_F="$RUNDIR/$OS.pid"
		PORT_F="$RUNDIR/$OS.port"

		if [ -e "$PID_F" ]; then
			printf 'The VM for "%s" is already running with PID %s.\n' \
				"$OS" "$(cat "$PID_F")" >&2
			exit 1
		fi

		PORT="$(free-port)"
		QCOW="$QCOW_DIR"/"$OS".qcow2

		# shellcheck disable=2086
		set -- qemu-system-x86_64 \
			-m 1G                                           \
			-nic user,model=virtio,hostfwd=tcp::"$PORT"-:22 \
			-drive file="$QCOW",media=disk,if=virtio        \
			-enable-kvm                                     \
			$FLAGS "$@"

		if [ "$DRY_RUN" = true ]; then
			echo "$@"
			exit
		fi

		if [ "$VERBOSE" = true ]; then
			set -x
		fi

		"$@" 1>>"$LOGS" 2>&1 &
		PID=$!
		set +x
		printf '%s' "$PID"  > "$PID_F"
		printf '%s' "$PORT" > "$PORT_F"

		write_ssh_config
		;;
	down)
		eval "$(assert-arg "$OS" 'OS')"
		shift
		if [ "${1:-}" = '--' ]; then
			shift
		fi

		OS="$(guess_name "$OS")"
		PID_F="$RUNDIR/$OS.pid"
		PORT_F="$RUNDIR/$OS.port"

		if [ ! -e "$PID_F" ]; then
			printf 'The VM for "%s" is not running, already.\n' "$OS" >&2
			exit 1
		fi

		PID="$(cat "$PID_F")"

		if [ "$DRY_RUN" = true ]; then
			echo rm -f "$PID_F" "$PORT_F"
			echo kill "$PID"
		else
			rm -f "$PID_F" "$PORT_F"
			kill "$PID"
		fi

		write_ssh_config
		;;
	*)
		printf 'Unrecognized action: "%s".\n\n' "$ACTION" >&2
		usage >&2
		exit 2
esac