#!/bin/sh

set -e

# paths to state file and definition dir
PState=/var/fsm/$2
PDef=/etc/fsm/$2

watch () {
    SO=$(cat $PState)
    SN=$(callOne $PDef/watch $SO "xxx" \
	"./$SO
         ./default
         /bin/false") || fail "watch script failed or missing"
    [ -n "$SN" ] || fail "watch script $S0 returned empty state name"
    change $SN
}

change () {
    SO=$(cat $PState)
    SN=$1
    if [ "$SO" != "$SN" ]; then
	if [ -x $PDef/trans/$SO-$SN.trans ]; then
	    # one script to handle whole transition
	    callOne $PDef/trans $SO $SN \
		"./$SO-$SN.trans" \
		|| fail "state transition script failed"
	else
	    # seperate scripts for leaving and entering states
	    callOne $PDef/trans $SO $SN \
		"./$SO.leave
                 ./default.leave
                 /bin/true" \
		|| fail "state leave script failed"
	    callOne $PDef/trans $SO $SN \
		"./$SN.enter
                 ./default.enter
                 /bin/true" \
		|| fail "state enter script failed"

	fi
	echo $SN > $PState
    fi
}

callOne () { # args: cwd arg1 arg2 cmdlist
    echo "$4" | sed 's/ *//' | (
	set -e
	cd $1
	while read cmd; do
	    if [ -x "$cmd" ]; then
		$cmd $2 $3
		exit $?
	    fi
	done )
}

fail() {
    echo "$1" 1>&2
    exit 1
}

printArgs () {
    fail "Usage:
$0 get    fsm
$0 watch  fsm
$0 change fsm state"
}

[ $# -lt 2 ] && printArgs

# check for minimal FSM definition
if [   -f $PDef/initial_state \
    -a -d $PDef/watch \
    -a -d $PDef/trans ]; then
    if [ ! -f $PState ]; then
	mkdir -p $(dirname $PState)
	S=$(cat $PDef/initial_state)
	[ -n "$S" ] || fail "initial state must not be empty"
	echo $S >$PState
    fi
else
    fail "FSM $1 does not exist"
fi

# lock state file (neccessary also for watch, as it calls scripts that
# assume a certain state as active during their whole execution time)
exec 666<$PState
flock -x 666

case "$1" in
    get)
	cat $PState
	;;
    watch)
	watch
	;;
    change)
	[ -n "$3" ] || printArgs
	change $3
	;;
    *)
	printArgs
esac