godot_simple_state_machine/state_machine.gd

extends Node

@onready var parent_node = get_parent()
var _transitions = []
var _transitions_by_source = {}
var _states = ['default']
var _current_state = 0
var _last_state = -1
var _current_state_duration = 0
var _triggers = {}
var _current_triggers = []

var _same_state_transitions_enabled = true
var _debug_enabled = false

func _ready():
	add_to_group("state_machine")

func _physics_process(delta):
	_current_state_duration += delta
	var state_changed = false
	var state_name = get_current_state()
	if _transitions_by_source.has(state_name):
		for transition_index in _transitions_by_source[state_name]:
			var transition = _transitions[transition_index]
			var trans_allowed = _same_state_transitions_enabled == true or state_name != transition['dest']
			if transition['trigger_name'] == '' or _current_triggers.has(transition['trigger_name']):
				if _are_conditions_valid(transition['conditions']) and trans_allowed:
					_change_state(transition['dest'])
					state_changed = true
					break

	if not state_changed:
		var update_name = _get_on_state_update_method_name(state_name)
		if parent_node.has_method(update_name):
			Callable(parent_node, update_name).call(delta)

	_current_triggers = []

func _are_conditions_valid(conditions):
	var condition_valid = true
	for condition in conditions:
		var not_condition_wanted = condition.begins_with('!')
		var condition_funcname = condition.substr(1, condition.length() - 1) if not_condition_wanted else condition
		var condition_func = Callable(parent_node, condition_funcname)
		var condition_met = condition_func.call()
		if not_condition_wanted:
			condition_met = not condition_met
		if not condition_met:
			condition_valid = false
			break
	return condition_valid

func set_same_state_transitions_enabled(val):
	_same_state_transitions_enabled = val

func set_debug_enabled(val):
	_debug_enabled = val

func get_current_state():
	return _states[_current_state]

func get_last_state():
	if _last_state == -1:
		return null
	return _states[_last_state]

func get_current_state_duration():
	return _current_state_duration

func add_state(name):
	if _states.count(name) == 0:
		_states.append(name)

func add_states(states):
	for state in states:
		if _states.count(state) == 0:
			_states.append(state)

func set_init_state(name):
	_change_state(name)

func _get_on_state_enter_method_name(state):
	return "on_" + state + "_state_enter"

func _get_on_state_update_method_name(state):
	return "on_" + state + "_state_update"

func _get_on_state_exit_method_name(state):
	return "on_" + state + "_state_exit"

func _change_state(name):
	var index = _states.find(name)
	if index != -1:
		var old_state = get_current_state()
		var exit_name = _get_on_state_exit_method_name(old_state)
		# TODO: do not always call triggers (costly?)
		trigger_all(exit_name)
		if parent_node.has_method(exit_name):
			Callable(parent_node, exit_name).call()

		_last_state = _current_state
		_current_state = index
		_current_state_duration = 0
		if _debug_enabled:
			print(get_parent().name, "'s new state: ", name)

		var enter_name = _get_on_state_enter_method_name(name)
		trigger_all(enter_name)
		if parent_node.has_method(enter_name):
			Callable(parent_node, enter_name).call()

# source: can be a string or an array of string
# values:
# - STATE: any known state
# - *: all the states (including dest)
# - ^STATE: all the states except STATE
# - -STATE: remove_at STATE from the previous states found in source
#   e.g. ['*', '-state1', '-state2', 'state1']
#   => will populate everything but state1 and state2 and then add state1
#   e.g. ['^state1']
#   => will populate everything but state1
func add_transition(source, dest, conditions, trigger_name=''):
	if not source:
		return

	var states = []
	if typeof(source) == TYPE_ARRAY:
		for state in source:
			states.append(state)
	else:
		states.append(source)

	var wanted_states = []
	for state in states:
		if state == "*":
			for state2 in _states:
				wanted_states.append(state2)
		elif state.begins_with("^"):
			var unwanted_state = state.lstrip("^")
			for state2 in _states:
				if state2 != unwanted_state:
					wanted_states.append(state2)
		elif state.begins_with("-"):
			var unwanted_state = state.lstrip("-")
			wanted_states.erase(unwanted_state)
		else:
			wanted_states.append(state)

	if wanted_states.size() > 1:
		for state in wanted_states:
			add_transition(state, dest, conditions, trigger_name)
		return

	source = wanted_states[0]

	var transition = {'source': source, 'dest': dest, 'conditions': conditions, 'trigger_name': trigger_name}
	_transitions.append(transition)
	var transition_index = _transitions.size() - 1

	if !_transitions_by_source.has(source):
		_transitions_by_source[source] = []
	_transitions_by_source[source].append(transition_index)

	if trigger_name:
		if !_triggers.has(trigger_name):
			_triggers[trigger_name] = []
		_triggers[trigger_name].append(transition_index)
	# dest: state
	# conditions: list of functions
	# trigger_signal: signal that can trigger the transition
	# transitions["idle"] = {
	#     "dest": "hurt",
	#     "conditions": [],
	#     "trigger_signal": "receive_attack"
	# }

func trigger(trigger_name):
	if not _current_triggers.has(trigger_name):
		_current_triggers.append(trigger_name)

func trigger_all(trigger_name):
	get_tree().call_group("state_machine", "trigger", String(get_parent().name) + "_" + trigger_name)