Lua 5.1 stringstream (pure)

stringstream.lua

local stringstream = {}
stringstream.__index = stringstream

function stringstream.create(str)
	local out = setmetatable({}, stringstream)
	out.buffer = str or ""
	out.pos = 0
	out.__index = stringstream

	return out
end

function stringstream.read(ss, num)
	if num == "*a" then
		if ss.pos == #ss.buffer then
			return nil
		end

		local out = ss.buffer:sub(ss.pos + 1)

		ss.pos = #ss.buffer
		return out
	elseif num <= 0 then
		return ""
	end

	local out = ss.buffer:sub(ss.pos + 1, ss.pos + num)
	if #out == 0 then return nil end

	ss.pos = math.min(ss.pos + num, #ss.buffer)
	return out
end

-- FIXME: Should overwrite string instead
function stringstream.write(ss, ...)
	local gap1 = ss.buffer:sub(1, ss.pos)
	local gap2 = ss.buffer:sub(ss.pos + 1)
	local con = {}

	for i, v in ipairs({...}) do
		con[i] = tostring(v)
	end

	con = table.concat(con)
	ss.pos = ss.pos + #con
	ss.buffer = gap1..con..gap2

	return true
end

function stringstream.seek(ss, whence, offset)
	whence = whence or "cur"

	if whence == "set" then
		ss.pos = offset or 0
	elseif whence == "cur" then
		ss.pos = ss.pos + (offset or 0)
	elseif whence == "end" then
		ss.pos = #ss.buffer + (offset or 0)
	else
		error("bad argument #1 to 'seek' (invalid option '"..tostring(whence).."')", 2)
	end

	ss.pos = math.min(math.max(ss.pos, 0), #ss.buffer)
	return ss.pos
end

setmetatable(stringstream, {
	__call = function(_, str)
		return stringstream.create(str)
	end
})

return stringstream