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path: root/src/libjin-lua/scripts/ai/state_machine.lua
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jin.ai = jin.ai or {} 

------------------------------------------------------------------------------------------------------------------
-- https://github.com/kyleconroy/lua-state-machine
------------------------------------------------------------------------------------------------------------------

local machine = {}
machine.__index = machine

local NONE = "none"
local ASYNC = "async"

local function call_handler(handler, params)
  if handler then
	return handler(unpack(params))
  end
end

local function create_transition(name)
  local can, to, from, params

  local function transition(self, ...)
	if self.asyncState == NONE then
	  can, to = self:can(name)
	  from = self.current
	  params = { self, name, from, to, ...}

	  if not can then return false end
	  self.currentTransitioningEvent = name

	  local beforeReturn = call_handler(self["onbefore" .. name], params)
	  local leaveReturn = call_handler(self["onleave" .. from], params)

	  if beforeReturn == false or leaveReturn == false then
		return false
	  end

	  self.asyncState = name .. "WaitingOnLeave"

	  if leaveReturn ~= ASYNC then
		transition(self, ...)
	  end
	  
	  return true
	elseif self.asyncState == name .. "WaitingOnLeave" then
	  self.current = to

	  local enterReturn = call_handler(self["onenter" .. to] or self["on" .. to], params)

	  self.asyncState = name .. "WaitingOnEnter"

	  if enterReturn ~= ASYNC then
		transition(self, ...)
	  end
	  
	  return true
	elseif self.asyncState == name .. "WaitingOnEnter" then
	  call_handler(self["onafter" .. name] or self["on" .. name], params)
	  call_handler(self["onstatechange"], params)
	  self.asyncState = NONE
	  self.currentTransitioningEvent = nil
	  return true
	else
	  if string.find(self.asyncState, "WaitingOnLeave") or string.find(self.asyncState, "WaitingOnEnter") then
		self.asyncState = NONE
		transition(self, ...)
		return true
	  end
	end

	self.currentTransitioningEvent = nil
	return false
  end

  return transition
end

local function add_to_map(map, event)
  if type(event.from) == 'string' then
	map[event.from] = event.to
  else
	for _, from in ipairs(event.from) do
	  map[from] = event.to
	end
  end
end

function machine.create(options)
  assert(options.events)

  local fsm = {}
  setmetatable(fsm, machine)

  fsm.options = options
  fsm.current = options.initial or 'none'
  fsm.asyncState = NONE
  fsm.events = {}

  for _, event in ipairs(options.events or {}) do
	local name = event.name
	fsm[name] = fsm[name] or create_transition(name)
	fsm.events[name] = fsm.events[name] or { map = {} }
	add_to_map(fsm.events[name].map, event)
  end
  
  for name, callback in pairs(options.callbacks or {}) do
	fsm[name] = callback
  end

  return fsm
end

function machine:is(state)
  return self.current == state
end

function machine:can(e)
  local event = self.events[e]
  local to = event and event.map[self.current] or event.map['*']
  return to ~= nil, to
end

function machine:cannot(e)
  return not self:can(e)
end

function machine:todot(filename)
  local dotfile = io.open(filename,'w')
  dotfile:write('digraph {\n')
  local transition = function(event,from,to)
	dotfile:write(string.format('%s -> %s [label=%s];\n',from,to,event))
  end
  for _, event in pairs(self.options.events) do
	if type(event.from) == 'table' then
	  for _, from in ipairs(event.from) do
		transition(event.name,from,event.to)
	  end
	else
	  transition(event.name,event.from,event.to)
	end
  end
  dotfile:write('}\n')
  dotfile:close()
end

function machine:transition(event)
  if self.currentTransitioningEvent == event then
	return self[self.currentTransitioningEvent](self)
  end
end

function machine:cancelTransition(event)
  if self.currentTransitioningEvent == event then
	self.asyncState = NONE
	self.currentTransitioningEvent = nil
  end
end

machine.NONE = NONE
machine.ASYNC = ASYNC

------------------------------------------------------------------------------------------------------------------
-- Export to Jin. 
------------------------------------------------------------------------------------------------------------------

jin.ai.newStateMachine = machine.create