tactree/init.lua

local Tactree = {}
local Nodes = {}

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.data[node] = node.data[node] or {}
	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 NodePrivateData(node)
	return node.data[node]
end

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

		local node_type = Nodes[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.Composite(name)
	return function(parent_type_name)
		return function(children)
			if Nodes[name] then
				error('node with name \'' .. name .. '\' already exists.',  2)
			else
				if not Nodes[parent_type_name] then error('no such node \'' .. name .. '\'', 2) end
				Nodes[name] = setmetatable({}, { __index = Nodes[parent_type_name] })
			end

			local node_type = Nodes[name]

			node_type.children = {}

			for _, child in ipairs(children) do
				if type(child) ~= 'string' then error('invalid child node', 2) end

				table.insert(node_type.children, child)
			end
		end
	end
end

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

	local node = {}
	node.children = {}
	node.start = NodeStart
	node.update = NodeUpdate
	node.private = NodePrivateData

	-- this will crash if there is a recursive structure
	-- find a way to prevent this?
	if Nodes[name].children then
		for _, child in ipairs(Nodes[name].children) do
			local cn = Tactree.Tree(child)
			cn.parent = node
			table.insert(node.children, cn)
		end
	end

	return setmetatable(node, { __index = Nodes[name] })
end

Tactree.Leaf 'Sequence'
{
	start = function(node)
		node:private().current_child = 1
		node.children[node:private().current_child]:start()
	end,
	tick = function(node)
		local result = node.children[node:private().current_child]:update()

		if type(result) == 'boolean' then
			if result then
				if node:private().current_child == #node.children then
					return true
				else
					node:private().current_child = node:private().current_child + 1
					node.children[node:private().current_child]:start()
				end
			else
				return false
			end
		end
	end
}

Tactree.Leaf 'Repeat'
{
	start = function(node)
		node.children[1]:start()
	end,
	tick = function(node)
		local result = node.children[1]:update()

		if type(result) == 'boolean' then
			if not result then return false end

			node.children[1]:start()
		end
	end
}

--[[
	Example usage
	-------------

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

	local tr = Tactree.Tree 'Pick up nearest object'

	tr:start{ ... } ( or, if you already have a table, tr:start(existing_table) )

	t:update()
]]--

return Tactree