local function trigram_to_value (a, b, c)
	return a * 25 + b * 5 + c
end


local function next_trigram (message, index)
	index = (index or 0) + 1
	local offset = (index - 1) * 3
	local a = message[offset + 1]
	if not a then
		return nil
	end
	return index, a, message[offset + 2], message[offset + 3]
end


local function next_value (message, index)
	local a, b, c
	index, a, b, c = next_trigram(message, index)
	if not index then
		return nil
	end
	return index, trigram_to_value(a, b, c)
end


local reading = {
	trigram_to_value = trigram_to_value,
	next_trigram = next_trigram,
	next_value = next_value,
}


function reading.trigrams (message, start)
	return next_trigram, message, start or 0
end


function reading.values (message, start)
	return next_value, message, start or 0
end


function reading.tvalues (message)
	local values = {}
	for _, value in reading.values(message) do
		table.insert(values, value)
	end
	return values
end


return reading