local format = require "format"
local stats = {}
local mt = {__index=stats}


local function new (name_or_obj, parent)
	if type(name_or_obj) == "string" then
		name_or_obj = {
			name = name_or_obj,
			parent = parent,
			letters = 0,
			length = 0,
			counts = {},
			children = {},
		}
	end
	return setmetatable(name_or_obj, mt)
end


function stats:add (value)
	local current = self.counts[value] or 0
	if current == 0 then
		self.letters = self.letters + 1
	end
	self.length = self.length + 1
	self.counts[value] = current + 1
	if self.parent then
		self.parent:add(value)
	end
end


function stats:sub (name)
	local child = new(name, self)
	table.insert(self.children, child)
	return child
end


function stats:ioc (letters)
	letters = letters or self.letters
	local subtotal = 0
	for _, count in pairs(self.counts) do
		subtotal = subtotal + count * (count - 1)
	end
	return subtotal / (self.length * (self.length - 1) / letters)
end


function stats:dump ()
	local function dump (stat)
		local letters = (stat.parent or {}).letters
		io.write(stat.name, "\t", stat.length, "\t", stat.letters, "\t", format.float(stat:ioc(letters)))
		if letters then
			io.write("\t", format.float(stat:ioc()))
		end
		print()
	end

	dump(self)
	for _, child in ipairs(self.children) do
		dump(child)
	end
end


return new