-- Prosody IM

-- Copyright (C) 2011-2013 Florian Zeitz

--

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

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

--

-- This is used to sort destination addresses by preference

-- during S2S connections.

-- We can't hand this off to getaddrinfo, since it blocks

local ip_commonPrefixLength = require"util.ip".commonPrefixLength

local function commonPrefixLength(ipA, ipB)

	local len = ip_commonPrefixLength(ipA, ipB);

	return len < 64 and len or 64;

end

local function t_sort(t, comp)

	for i = 1, (#t - 1) do

		for j = (i + 1), #t do

			local a, b = t[i], t[j];

			if not comp(a,b) then

				t[i], t[j] = b, a;

			end

		end

	end

end

local function source(dest, candidates)

	local function comp(ipA, ipB)

		-- Rule 1: Prefer same address

		if dest == ipA then

			return true;

		elseif dest == ipB then

			return false;

		end

		-- Rule 2: Prefer appropriate scope

		if ipA.scope < ipB.scope then

			if ipA.scope < dest.scope then

				return false;

			else

				return true;

			end

		elseif ipA.scope > ipB.scope then

			if ipB.scope < dest.scope then

				return true;

			else

				return false;

			end

		end

		-- Rule 3: Avoid deprecated addresses

		-- XXX: No way to determine this

		-- Rule 4: Prefer home addresses

		-- XXX: Mobility Address related, no way to determine this

		-- Rule 5: Prefer outgoing interface

		-- XXX: Interface to address relation. No way to determine this

		-- Rule 6: Prefer matching label

		if ipA.label == dest.label and ipB.label ~= dest.label then

			return true;

		elseif ipB.label == dest.label and ipA.label ~= dest.label then

			return false;

		end

		-- Rule 7: Prefer temporary addresses (over public ones)

		-- XXX: No way to determine this

		-- Rule 8: Use longest matching prefix

		if commonPrefixLength(ipA, dest) > commonPrefixLength(ipB, dest) then

			return true;

		else

			return false;

		end

	end

	t_sort(candidates, comp);

	return candidates[1];

end

local function destination(candidates, sources)

	local sourceAddrs = {};

	local function comp(ipA, ipB)

		local ipAsource = sourceAddrs[ipA];

		local ipBsource = sourceAddrs[ipB];

		-- Rule 1: Avoid unusable destinations

		-- XXX: No such information

		-- Rule 2: Prefer matching scope

		if ipA.scope == ipAsource.scope and ipB.scope ~= ipBsource.scope then

			return true;

		elseif ipA.scope ~= ipAsource.scope and ipB.scope == ipBsource.scope then

			return false;

		end

		-- Rule 3: Avoid deprecated addresses

		-- XXX: No way to determine this

		-- Rule 4: Prefer home addresses

		-- XXX: Mobility Address related, no way to determine this

		-- Rule 5: Prefer matching label

		if ipAsource.label == ipA.label and ipBsource.label ~= ipB.label then

			return true;

		elseif ipBsource.label == ipB.label and ipAsource.label ~= ipA.label then

			return false;

		end

		-- Rule 6: Prefer higher precedence

		if ipA.precedence > ipB.precedence then

			return true;

		elseif ipA.precedence < ipB.precedence then

			return false;

		end

		-- Rule 7: Prefer native transport

		-- XXX: No way to determine this

		-- Rule 8: Prefer smaller scope

		if ipA.scope < ipB.scope then

			return true;

		elseif ipA.scope > ipB.scope then

			return false;

		end

		-- Rule 9: Use longest matching prefix

		if commonPrefixLength(ipA, ipAsource) > commonPrefixLength(ipB, ipBsource) then

			return true;

		elseif commonPrefixLength(ipA, ipAsource) < commonPrefixLength(ipB, ipBsource) then

			return false;

		end

		-- Rule 10: Otherwise, leave order unchanged

		return true;

	end

	for _, ip in ipairs(candidates) do

		sourceAddrs[ip] = source(ip, sources);

	end

	t_sort(candidates, comp);

	return candidates;

end

return {source = source,

	destination = destination};