local Tactree = {}
local Registry = {}

local function NodeStart(node, args)
	-- abort if started
	if node.data then return end

	node.data = node.parent and node.parent.data or args
	node:_start()
end

local function NodeUpdate(node)
	-- abort if not started
	if not node.data then return end

	local result = node:_tick()

	if type(result) == 'boolean' then
		node:_finish()

		node.data = nil
	end

	return result
end

local function default_impl(node) end
function Tactree.Node(name)
	return function(t)
		if Registry[name] then
			error('node with name \'' .. name .. '\' already exists.',  2)
		else
			Registry[name] = {}
		end

		local node_type = Registry[name]

		local tick = t.tick or t[1]
		if type(tick) ~= 'function' then error('no tick function supplied', 2) end

		node_type._tick = tick
		node_type._start = type(t.start) == 'function' and t.start or default_impl
		node_type._finish = type(t.finish) == 'function' and t.finish or default_impl
	end
end

function Tactree.Tree(name)
	if not Registry[name] then error('no such node \'' .. name .. '\'', 2) end

	local node = setmetatable({}, { __index = Registry[name] })
	node.children = {}
	node.start = NodeStart
	node.update = NodeUpdate

	return function(children)
		if type(children) == 'table' then
			for _, child in ipairs(children) do
				if type(child) == 'string' then
					child = Tactree.Tree(child)
				elseif type(child) ~= 'table' then
					error('invalid child type: ' .. type(child), 2)
				end

				child.parent = node
				table.insert(node.children, child)
			end
		end

		return node
	end
end

--[[
	Tactree.Node 'Find nearest object' { function (node) ... end }
	Tactree.Node 'Pick up object' { function (node) ... end}
	Tactree.Node 'Move' { function (node) return node.data.creature:move(node.data.tx, node.data.ty, dt) end }

	local t = Tactree.Tree 'Sequence' { 'Find nearest object', 'Move', 'Pick up object' }

	t:start(...)

	t:update()
]]--

return Tactree