local module = {}
setmetatable(module, {__index=_G})
setfenv(1, module)


--===== filters =====--


Filter = {}

-- base filter creation
function Filter.new(_, operation, tbl)
	local self = {}
	self.keys = {}
	self.filters = {}
	self.op = operation

	for _, v in ipairs(tbl) do
		if type(v) == "function" then
			table.insert(self.filters, v)
		elseif type(v) == "string" then
			table.insert(self.keys, v)
		end
	end

	return function(entity) 
		return Filter.check(self, entity)
	end
end
setmetatable(Filter, {__call=Filter.new})


-- base filter checking
function Filter.check(self, entity)
	local funcname = "check" .. self.op
	return Filter[funcname](self, entity)
end


-- AND filter (all keys and subfilters must match)
function Filter.AND(tbl)
	return Filter("AND", tbl)
end
function Filter.checkAND(self, entity)
	for _, subfilter in ipairs(self.filters) do
		if not subfilter(entity) then return false end
	end
	for _, key in ipairs(self.keys) do
		if entity[key] == nil then return false end
	end
	return true
end


-- OR filter (at least one key or subfilter must match)
function Filter.OR(tbl)
	return Filter("OR", tbl)
end
function Filter.checkOR(self, entity)
	for _, subfilter in ipairs(self.filters) do
		if subfilter(entity) then return true end
	end
	for _, key in ipairs(self.keys) do
		if entity[key] ~= nil then return true end
	end
	return false
end


-- NAND filter (at least one key or subfilter must NOT match)
function Filter.NAND(tbl)
	return Filter("NAND", tbl)
end
function Filter.checkNAND(self, entity)
	for _, subfilter in ipairs(self.filters) do
		if not subfilter(entity) then return true end
	end
	for _, key in ipairs(self.keys) do
		if entity[key] == nil then return true end
	end
	return false
end


-- NOR filter (no keys or subfilters may match)
function Filter.NOR(tbl)
	return Filter("NOR", tbl)
end
function Filter.checkNOR(self, entity)
	for _, subfilter in ipairs(self.filters) do
		if subfilter(entity) then return false end
	end
	for _, key in ipairs(self.keys) do
		if entity[key] ~= nil then return false end
	end
	return true
end


return module