Add statemachine module

vlib/statemachine/statemachine.v

@@ -0,0 +1,66 @@
+module statemachine
+
+pub type EventHandlerFn = fn (receiver voidptr)
+pub type ConditionFn = fn (receiver voidptr) bool
+
+struct State {
+mut:
+	entry_handler EventHandlerFn
+	run_handler   EventHandlerFn
+	exit_handler  EventHandlerFn
+}
+
+struct Transition {
+mut:
+	to string
+	condition ConditionFn
+}
+
+struct StateMachine {
+mut:
+	states      map[string]State
+	transitions map[string]Transition
+	current_state string
+}
+
+
+pub fn new() &StateMachine {
+	return &StateMachine{}
+}
+
+pub fn (mut s StateMachine) add_state(name string, entry EventHandlerFn, run EventHandlerFn, exit EventHandlerFn) {
+	s.states [name] = State{
+		entry_handler: entry
+		run_handler: run
+		exit_handler: exit
+	}
+	if s.states.len == 1 {
+		s.current_state = name
+	}
+}
+
+pub fn (mut s StateMachine) add_transition(from string, to string, condition ConditionFn) {
+	s.transitions[from] = Transition{
+		to: to
+		condition: condition
+	}
+}
+
+pub fn (mut s StateMachine) run(receiver voidptr){
+	for from_state, transition in s.transitions{
+		if from_state in s.states {
+			if transition.condition(receiver){
+				s.change_state(receiver, s.transitions[from_state].to)
+			}
+		}
+	}
+}
+
+pub fn (mut s StateMachine) change_state(receiver voidptr, newstate string){
+	mut current_state := s.current_state
+	s.states[current_state].exit_handler(receiver)
+	current_state = newstate
+	s.states[current_state].run_handler(receiver)
+	s.states[current_state].entry_handler(receiver)
+	s.current_state = current_state
+}

vlib/statemachine/statemachine_test.v

@@ -0,0 +1,34 @@
+import statemachine
+
+struct FakeReceiver {
+mut:
+	data []string
+}
+
+fn test_statemachine_works_when_typical() {
+	mut receiver := &FakeReceiver{}
+	mut s := statemachine.new()
+	s.add_state("A",on_test_entry, on_test_run, on_test_exit)
+	s.add_state("B",on_test_entry, on_test_run, on_test_exit)
+	s.add_transition("A", "B", condition_a_b)
+	s.run(receiver)
+
+	assert receiver.data[0] == "on_test_exit"
+	assert receiver.data[1] == "on_test_run"
+	assert receiver.data[2] == "on_test_entry"
+
+}
+
+fn on_test_entry(mut receiver &FakeReceiver) {
+	receiver.data << "on_test_entry"
+}
+fn on_test_run(mut receiver &FakeReceiver) {
+	receiver.data << "on_test_run"
+}
+fn on_test_exit(mut receiver &FakeReceiver) {
+	receiver.data << "on_test_exit"
+}
+
+fn condition_a_b(receiver &FakeReceiver) bool {
+	return true
+}