-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--

local ipairs, pairs, setmetatable, next, tostring =
      ipairs, pairs, setmetatable, next, tostring;
local getmetatable = getmetatable;
local t_concat = table.concat;

local _ENV = nil;
-- luacheck: std none

local set_mt = { __name = "set" };
function set_mt.__call(set, _, k)
	return next(set._items, k);
end

local items_mt = {};
function items_mt.__call(items, _, k)
	return next(items, k);
end

function set_mt:__freeze()
	local a, i = {}, 1;
	for item in self._items do
		a[i], i = item, i+1;
	end
	return a;
end

local function is_set(o)
	local mt = getmetatable(o);
	return mt == set_mt;
end

local function new(list)
	local items = setmetatable({}, items_mt);
	local set = { _items = items };

	-- We access the set through an upvalue in these methods, so ignore 'self' being unused
	--luacheck: ignore 212/self

	function set:add(item)
		items[item] = true;
	end

	function set:contains(item)
		return items[item];
	end

	function set:items()
		return next, items;
	end

	function set:remove(item)
		items[item] = nil;
	end

	function set:add_list(item_list)
		if item_list then
			for _, item in ipairs(item_list) do
				items[item] = true;
			end
		end
	end

	function set:include(otherset)
		for item in otherset do
			items[item] = true;
		end
	end

	function set:exclude(otherset)
		for item in otherset do
			items[item] = nil;
		end
	end

	function set:empty()
		return not next(items);
	end

	if list then
		set:add_list(list);
	end

	return setmetatable(set, set_mt);
end

local function union(set1, set2)
	local set = new();
	local items = set._items;

	for item in pairs(set1._items) do
		items[item] = true;
	end

	for item in pairs(set2._items) do
		items[item] = true;
	end

	return set;
end

local function difference(set1, set2)
	local set = new();
	local items = set._items;

	for item in pairs(set1._items) do
		items[item] = (not set2._items[item]) or nil;
	end

	return set;
end

local function intersection(set1, set2)
	local set = new();
	local items = set._items;

	set1, set2 = set1._items, set2._items;

	for item in pairs(set1) do
		items[item] = (not not set2[item]) or nil;
	end

	return set;
end

local function xor(set1, set2)
	return union(set1, set2) - intersection(set1, set2);
end

function set_mt.__add(set1, set2)
	return union(set1, set2);
end
function set_mt.__sub(set1, set2)
	return difference(set1, set2);
end
function set_mt.__div(set, func)
	local new_set = new();
	local items, new_items = set._items, new_set._items;
	for item in pairs(items) do
		local new_item = func(item);
		if new_item ~= nil then
			new_items[new_item] = true;
		end
	end
	return new_set;
end
function set_mt.__eq(set1, set2)
	if getmetatable(set1) ~= set_mt or getmetatable(set2) ~= set_mt then
		-- Lua 5.3+ calls this if both operands are tables, even if metatables differ
		return false;
	end

	set1, set2 = set1._items, set2._items;
	for item in pairs(set1) do
		if not set2[item] then
			return false;
		end
	end

	for item in pairs(set2) do
		if not set1[item] then
			return false;
		end
	end

	return true;
end
function set_mt.__tostring(set)
	local s, items = { }, set._items;
	for item in pairs(items) do
		s[#s+1] = tostring(item);
	end
	return t_concat(s, ", ");
end

return {
	new = new;
	is_set = is_set;
	union = union;
	difference = difference;
	intersection = intersection;
	xor = xor;
};