From 3cdfdd14a5ac1de36f41981a6ed69b0f9f2fd90d Mon Sep 17 00:00:00 2001
From: BadToad2000 <jameson.miller@outlook.com>
Date: Sun, 28 Feb 2016 23:34:13 -0600
Subject: [PATCH] When attempting to replace a bag with a smaller bag, ensure
 the items beyond the last index of the smaller bag are not lost.

If there is sufficient space in the smaller bag, move the items to the front.
Otherwise disallow the replacement.
---
 bags.lua | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/bags.lua b/bags.lua
index 3b86544..0dd391b 100644
--- a/bags.lua
+++ b/bags.lua
@@ -144,11 +144,36 @@ minetest.register_on_joinplayer(function(player)
 			player:get_inventory():set_stack(listname, index, nil)
 		end,
 		allow_put = function(inv, listname, index, stack, player)
-			if stack:get_definition().groups.bagslots then
-				return 1
-			else
-				return 0
+			local new_slots = stack:get_definition().groups.bagslots
+			if new_slots then
+				local player_inv = player:get_inventory()
+				local old_slots = player_inv:get_size(listname.."contents")
+
+				if new_slots >= old_slots then
+					return 1
+				else
+					-- using a smaller bag, make sure it fits
+					local old_list = player_inv:get_list(listname.."contents")
+					local new_list = {}
+					local slots_used = 0
+					local use_new_list = false
+
+					for i, v in ipairs(old_list) do
+						if v and not v:is_empty() then
+							slots_used = slots_used + 1
+							use_new_list = i > new_slots
+							new_list[slots_used] = v
+						end
+					end
+					if new_slots >= slots_used then
+						if use_new_list then
+							player_inv:set_list(listname.."contents", new_list)
+						end
+						return 1
+					end
+				end
 			end
+			return 0
 		end,
 		allow_take = function(inv, listname, index, stack, player)
 			if player:get_inventory():is_empty(listname.."contents") then