local queue = require("util.queue");

local lib = { smqueue = {} }

local smqueue = lib.smqueue;

function smqueue:push(v)

	self._head = self._head + 1;

	assert(self._queue:push(v));

end

function smqueue:ack(h)

	if h < self._tail then

		return nil, "tail"

	elseif h > self._head then

		return nil, "head"

	end

	local acked = {};

	self._tail = h;

	local expect = self._head - self._tail;

	while expect < self._queue:count() do

		local v = self._queue:pop();

		if not v then return nil, "pop" end

		table.insert(acked, v);

	end

	return acked

end

function smqueue:count_unacked() return self._head - self._tail end

function smqueue:count_acked() return self._tail end

function smqueue:resumable() return self._queue:count() >= (self._head - self._tail) end

function smqueue:resume() return self._queue:items() end

function smqueue:consume() return self._queue:consume() end

function smqueue:table()

	local t = {};

	for i, v in self:resume() do t[i] = v; end

	return t

end

local function freeze(q) return { head = q._head; tail = q._tail } end

local queue_mt = { __name = "smqueue"; __index = smqueue; __len = smqueue.count_unacked; __freeze = freeze }

function lib.new(size)

	assert(size > 0);

	return setmetatable({ _head = 0; _tail = 0; _queue = queue.new(size, true) }, queue_mt)

end

return lib