-- Prosody IM

-- Copyright (C) 2008-2015 Matthew Wild

-- Copyright (C) 2008-2015 Waqas Hussain

--

-- This project is MIT/X11 licensed. Please see the

-- COPYING file in the source package for more information.

--

-- Small ringbuffer library (i.e. an efficient FIFO queue with a size limit)

-- (because unbounded dynamically-growing queues are a bad thing...)

local have_utable, utable = pcall(require, "util.table"); -- For pre-allocation of table

local function new(size, allow_wrapping)

	-- Head is next insert, tail is next read

	local head, tail = 1, 1;

	local items = 0; -- Number of stored items

	local t = have_utable and utable.create(size, 0) or {}; -- Table to hold items

	--luacheck: ignore 212/self

	return {

		_items = t;

		size = size;

		count = function (self) return items; end;

		push = function (self, item)

			if items >= size then

				if allow_wrapping then

					tail = (tail%size)+1; -- Advance to next oldest item

					items = items - 1;

				else

					return nil, "queue full";

				end

			end

			t[head] = item;

			items = items + 1;

			head = (head%size)+1;

			return true;

		end;

		pop = function (self)

			if items == 0 then

				return nil;

			end

			local item;

			item, t[tail] = t[tail], 0;

			tail = (tail%size)+1;

			items = items - 1;

			return item;

		end;

		peek = function (self)

			if items == 0 then

				return nil;

			end

			return t[tail];

		end;

		replace = function (self, data)

			if items == 0 then

				return self:push(data);

			end

			t[tail] = data;

			return true;

		end;

		items = function (self)

			--luacheck: ignore 431/t

			return function (t, pos)

				if pos >= t:count() then

					return nil;

				end

				local read_pos = tail + pos;

				if read_pos > t.size then

					read_pos = (read_pos%size);

				end

				return pos+1, t._items[read_pos];

			end, self, 0;

		end;

	};

end

return {

	new = new;

};