From 5b7f1813ce1107a2b96e439ad60f6676b9b9699f Mon Sep 17 00:00:00 2001
From: Bluebird <bluebird.greycoat@gmail.com>
Date: Wed, 11 Mar 2015 13:32:30 -0500
Subject: [PATCH] Improve upgrade handling to allow an arbitrary number of
 upgrades.

Main changes included:
1) Upgrade handling code can now handle an arbitrary number of upgrades.
2) Compatibility code to move upgrade items to the new upgrade inventory.
3) Registrations (power requirement tables, etc.) were updated so they no longer assume a fixed upgrade size.
4) Wrench registrations include the new inventory name.
---
 technic/machines/LV/alloy_furnace.lua      |   2 +-
 technic/machines/LV/compressor.lua         |   2 +-
 technic/machines/LV/electric_furnace.lua   |   2 +-
 technic/machines/LV/extractor.lua          |   2 +-
 technic/machines/LV/grinder.lua            |   2 +-
 technic/machines/MV/alloy_furnace.lua      |   2 +-
 technic/machines/MV/centrifuge.lua         |   3 +-
 technic/machines/MV/electric_furnace.lua   |   4 +-
 technic/machines/MV/extractor.lua          |   2 +-
 technic/machines/MV/grinder.lua            |   2 +-
 technic/machines/MV/tool_workshop.lua      |  25 ++-
 technic/machines/register/battery_box.lua  |  29 +--
 technic/machines/register/common.lua       | 250 ++++++++++++++-------
 technic/machines/register/machine_base.lua |  32 ++-
 wrench/technic.lua                         |  26 +--
 15 files changed, 241 insertions(+), 144 deletions(-)

diff --git a/technic/machines/LV/alloy_furnace.lua b/technic/machines/LV/alloy_furnace.lua
index bdf2f31..56f0037 100644
--- a/technic/machines/LV/alloy_furnace.lua
+++ b/technic/machines/LV/alloy_furnace.lua
@@ -10,5 +10,5 @@ minetest.register_craft({
 	}
 })
 
-technic.register_alloy_furnace({tier = "LV", speed = 1, demand = {300}})
+technic.register_alloy_furnace({tier = "LV", speed = 1, demand = 300})
 
diff --git a/technic/machines/LV/compressor.lua b/technic/machines/LV/compressor.lua
index e2bde40..3344615 100644
--- a/technic/machines/LV/compressor.lua
+++ b/technic/machines/LV/compressor.lua
@@ -10,4 +10,4 @@ minetest.register_craft({
 	}
 })
 
-technic.register_compressor({tier = "LV", demand = {300}, speed = 1})
+technic.register_compressor({tier = "LV", demand = 300, speed = 1})
diff --git a/technic/machines/LV/electric_furnace.lua b/technic/machines/LV/electric_furnace.lua
index cc4daff..c083e7e 100644
--- a/technic/machines/LV/electric_furnace.lua
+++ b/technic/machines/LV/electric_furnace.lua
@@ -11,6 +11,6 @@ minetest.register_craft({
 	}
 })
 
-technic.register_electric_furnace({tier="LV", demand={300}, speed = 2})
+technic.register_electric_furnace({tier="LV", demand=300, speed = 2})
 
 
diff --git a/technic/machines/LV/extractor.lua b/technic/machines/LV/extractor.lua
index 363d2e3..86aea5c 100644
--- a/technic/machines/LV/extractor.lua
+++ b/technic/machines/LV/extractor.lua
@@ -10,4 +10,4 @@ minetest.register_craft({
 	}
 })
 
-technic.register_extractor({tier = "LV", demand = {300}, speed = 1})
+technic.register_extractor({tier = "LV", demand = 300, speed = 1})
diff --git a/technic/machines/LV/grinder.lua b/technic/machines/LV/grinder.lua
index da9ea29..ba8aa92 100644
--- a/technic/machines/LV/grinder.lua
+++ b/technic/machines/LV/grinder.lua
@@ -9,5 +9,5 @@ minetest.register_craft({
 	}
 })
 
-technic.register_grinder({tier="LV", demand={200}, speed=1})
+technic.register_grinder({tier="LV", demand=200, speed=1})
 
diff --git a/technic/machines/MV/alloy_furnace.lua b/technic/machines/MV/alloy_furnace.lua
index a1918fd..ae08350 100644
--- a/technic/machines/MV/alloy_furnace.lua
+++ b/technic/machines/MV/alloy_furnace.lua
@@ -10,5 +10,5 @@ minetest.register_craft({
 })
 
 
-technic.register_alloy_furnace({tier = "MV", speed = 1.5, upgrade = 1, tube = 1, demand = {3000, 2000, 1000}})
+technic.register_alloy_furnace({tier = "MV", speed = 1.5, upgrade = 1, tube = 1, demand = 3000, demand_reduction_factor=0.65 })
 
diff --git a/technic/machines/MV/centrifuge.lua b/technic/machines/MV/centrifuge.lua
index 5bf24bf..087dd46 100644
--- a/technic/machines/MV/centrifuge.lua
+++ b/technic/machines/MV/centrifuge.lua
@@ -9,7 +9,8 @@ minetest.register_craft({
 
 technic.register_centrifuge({
 	tier = "MV",
-	demand = { 8000, 7000, 6000 },
+	demand = 8000,
+	demand_reduction_factor=0.25,
 	speed = 2,
 	upgrade = 1,
 	tube = 1,
diff --git a/technic/machines/MV/electric_furnace.lua b/technic/machines/MV/electric_furnace.lua
index 1f6b1c2..97f583f 100644
--- a/technic/machines/MV/electric_furnace.lua
+++ b/technic/machines/MV/electric_furnace.lua
@@ -9,10 +9,10 @@ minetest.register_craft({
 	output = 'technic:mv_electric_furnace',
 	recipe = {
 		{'technic:stainless_steel_ingot', 'technic:lv_electric_furnace', 'technic:stainless_steel_ingot'},
-		{'pipeworks:tube_1',         'technic:mv_transformer',      'pipeworks:tube_1'},
+		{'pipeworks:tube_1',              'technic:mv_transformer',      'pipeworks:tube_1'},
 		{'technic:stainless_steel_ingot', 'technic:mv_cable0',           'technic:stainless_steel_ingot'},
 	}
 })
 
-technic.register_electric_furnace({tier="MV", upgrade=1, tube=1, demand={2000, 1000, 500}, speed=4})
+technic.register_electric_furnace({tier="MV", upgrade=1, tube=1, demand=2000, demand_reduction_factor=0.75, speed=4})
 
diff --git a/technic/machines/MV/extractor.lua b/technic/machines/MV/extractor.lua
index fdef5b2..e3103e0 100644
--- a/technic/machines/MV/extractor.lua
+++ b/technic/machines/MV/extractor.lua
@@ -9,4 +9,4 @@ minetest.register_craft({
 	}
 })
 
-technic.register_extractor({tier = "MV", demand = {800, 600, 400}, speed = 2, upgrade = 1, tube = 1})
+technic.register_extractor({tier = "MV", demand = 800, demand_reduction_factor=0.5, speed = 2, upgrade = 1, tube = 1})
diff --git a/technic/machines/MV/grinder.lua b/technic/machines/MV/grinder.lua
index dac536c..2a5f3cf 100644
--- a/technic/machines/MV/grinder.lua
+++ b/technic/machines/MV/grinder.lua
@@ -9,5 +9,5 @@ minetest.register_craft({
 	}
 })
 
-technic.register_grinder({tier="MV", demand={600, 450, 300}, speed=2, upgrade=1, tube=1})
+technic.register_grinder({tier="MV", demand=600, demand_reduction_factor=0.5, speed=2, upgrade=1, tube=1})
 
diff --git a/technic/machines/MV/tool_workshop.lua b/technic/machines/MV/tool_workshop.lua
index cc54001..3cdad4a 100644
--- a/technic/machines/MV/tool_workshop.lua
+++ b/technic/machines/MV/tool_workshop.lua
@@ -14,14 +14,15 @@ minetest.register_craft({
 	}
 })
 
-local workshop_demand = {5000, 3500, 2000}
+local workshop_demand = 5000
+local workshop_demand_reduction_factor = 0.6
+local num_upgrade_slots = 2
 
 local workshop_formspec =
 	"invsize[8,9;]"..
 	"list[current_name;src;3,1;1,1;]"..
 	"label[0,0;"..S("%s Tool Workshop"):format("MV").."]"..
-	"list[current_name;upgrade1;1,3;1,1;]"..
-	"list[current_name;upgrade2;2,3;1,1;]"..
+	"list[current_name;upgrades;1,3;" .. num_upgrade_slots .. ",1;]"..
 	"label[1,4;"..S("Upgrade Slots").."]"..
 	"list[current_player;main;0,5;8,4;]"..
 	"listring[current_player;main]"..
@@ -41,13 +42,20 @@ local run = function(pos, node)
 
 	-- Setup meta data if it does not exist.
 	if not eu_input then
-		meta:set_int("MV_EU_demand", workshop_demand[1])
+		meta:set_int("MV_EU_demand", workshop_demand)
 		meta:set_int("MV_EU_input", 0)
 		return
 	end
 
+	-- Do compatibility updates if needed.
+	technic.transfer_upgrades_to_new_upgrade_inventory(meta, formspec, num_upgrade_slots)
+
 	local EU_upgrade, tube_upgrade = technic.handle_machine_upgrades(meta)
 
+	-- Calculate the required EUs based on the normalized number of battery upgrades.
+	local norm_eu_upgrade = technic.normalize_value(EU_upgrade, 0, num_upgrade_slots)
+	local total_required_power = workshop_demand - ((workshop_demand * workshop_demand_reduction_factor) * norm_eu_upgrade)
+
 	local repairable = false
 	local srcstack = inv:get_stack("src", 1)
 	if not srcstack:is_empty() then
@@ -70,14 +78,14 @@ local run = function(pos, node)
 		return
 	end
 	
-	if eu_input < workshop_demand[EU_upgrade+1] then
+	if eu_input < total_required_power then
 		meta:set_string("infotext", S("%s Unpowered"):format(machine_name))
-	elseif eu_input >= workshop_demand[EU_upgrade+1] then
+	elseif eu_input >= total_required_power then
 		meta:set_string("infotext", S("%s Active"):format(machine_name))
 		srcstack:add_wear(-1000)
 		inv:set_stack("src", 1, srcstack)
 	end
-	meta:set_int("MV_EU_demand", workshop_demand[EU_upgrade+1])
+	meta:set_int("MV_EU_demand", total_required_power)
 end
 
 minetest.register_node("technic:tool_workshop", {
@@ -92,8 +100,7 @@ minetest.register_node("technic:tool_workshop", {
 		meta:set_string("formspec", workshop_formspec)
 		local inv = meta:get_inventory()
 		inv:set_size("src", 1)
-		inv:set_size("upgrade1", 1)
-		inv:set_size("upgrade2", 1)
+		inv:set_size("upgrades", num_upgrade_slots)
 	end,	
 	can_dig = technic.machine_can_dig,
 	allow_metadata_inventory_put = technic.machine_inventory_put,
diff --git a/technic/machines/register/battery_box.lua b/technic/machines/register/battery_box.lua
index 82edca0..ecf45ba 100644
--- a/technic/machines/register/battery_box.lua
+++ b/technic/machines/register/battery_box.lua
@@ -77,14 +77,13 @@ function technic.register_battery_box(data)
 		"listring[current_name;src]"..
 		"listring[current_player;main]"
 
+	local num_upgrade_slots = 2
+
 	if data.upgrade then
 		formspec = formspec..
-			"list[current_name;upgrade1;3.5,3;1,1;]"..
-			"list[current_name;upgrade2;4.5,3;1,1;]"..
-			"label[3.5,4;"..S("Upgrade Slots").."]"..
-			"listring[current_name;upgrade1]"..
-			"listring[current_player;main]"..
-			"listring[current_name;upgrade2]"..
+			"list[current_name;upgrades;3,3;"..num_upgrade_slots..",1;]"..
+			"label[3,4;"..S("Upgrade Slots").."]"..
+			"listring[current_name;upgrades]"..
 			"listring[current_player;main]"
 	end
 
@@ -93,12 +92,15 @@ function technic.register_battery_box(data)
 		local eu_input       = meta:get_int(tier.."_EU_input")
 		local current_charge = meta:get_int("internal_EU_charge")
 
+		-- Do compatibility updates if needed.
+		technic.transfer_upgrades_to_new_upgrade_inventory(meta, formspec, num_upgrade_slots)
+
 		local EU_upgrade, tube_upgrade = 0, 0
 		if data.upgrade then
 			EU_upgrade, tube_upgrade = technic.handle_machine_upgrades(meta)
 		end
 		local max_charge = data.max_charge * (1 + EU_upgrade / 10)
-			
+
 		-- Charge/discharge the battery with the input EUs
 		if eu_input >= 0 then
 			current_charge = math.min(current_charge + eu_input, max_charge)
@@ -113,7 +115,7 @@ function technic.register_battery_box(data)
 		current_charge, tool_empty = technic.discharge_tools(meta,
 				current_charge, data.discharge_step,
 				max_charge)
-			
+
 		if data.tube then
 			local inv = meta:get_inventory()
 			technic.handle_machine_pipeworks(pos, tube_upgrade,
@@ -173,10 +175,10 @@ function technic.register_battery_box(data)
 			description = S("%s Battery Box"):format(tier),
 			tiles = {"technic_"..ltier.."_battery_box_top.png",
 			         "technic_"..ltier.."_battery_box_bottom.png",
-				 "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png",
-				 "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png",
-				 "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png",
-				 "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png"},
+			         "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png",
+			         "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png",
+			         "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png",
+			         "technic_"..ltier.."_battery_box_side.png^technic_power_meter"..i..".png"},
 			groups = groups,
 			tube = data.tube and tube or nil,
 			paramtype2 = "facedir",
@@ -195,8 +197,7 @@ function technic.register_battery_box(data)
 				meta:set_float("internal_EU_charge", 0)
 				inv:set_size("src", 1)
 				inv:set_size("dst", 1)
-				inv:set_size("upgrade1", 1)
-				inv:set_size("upgrade2", 1)
+				inv:set_size("upgrades", num_upgrade_slots)
 			end,
 			can_dig = technic.machine_can_dig,
 			allow_metadata_inventory_put = technic.machine_inventory_put,
diff --git a/technic/machines/register/common.lua b/technic/machines/register/common.lua
index aa8ec9c..e573d30 100644
--- a/technic/machines/register/common.lua
+++ b/technic/machines/register/common.lua
@@ -1,65 +1,134 @@
 
 local S = technic.getter
 
--- handles the machine upgrades every tick
-function technic.handle_machine_upgrades(meta)
-	-- Get the names of the upgrades
+
+
+-- A function to normalize a value. The output floating-point value should
+-- always be in the range [0, 1].
+function technic.normalize_value(value, lower, upper)
+	value = value - lower
+	upper = upper - lower
+	return value / upper
+end
+
+
+
+-- This function is defined because the same compatibility code needs to be run
+-- in three different places. This function can be removed once we are
+-- reasonably sure that everyone is updated.
+function technic.transfer_upgrades_to_new_upgrade_inventory(meta, new_formspec, new_inv_size)
 	local inv = meta:get_inventory()
 
-	local srcstack = inv:get_stack("upgrade1", 1)
-	local upg_item1 = srcstack and srcstack:get_name()
-
-	srcstack = inv:get_stack("upgrade2", 1)
-	local upg_item2 = srcstack and srcstack:get_name()
-
-	-- Save some power by installing battery upgrades.
-	-- Tube loading speed can be upgraded using control logic units.
-	local EU_upgrade = 0
-	local tube_upgrade = 0
-
-	if upg_item1 == "technic:control_logic_unit" then
-		tube_upgrade = tube_upgrade + 1
-	elseif upg_item1 == "technic:battery" then
-		EU_upgrade = EU_upgrade + 1
+	-- Compatibility code. Move upgrade items from the (now depreciated)
+	-- upgrade inventory lists into the new unified upgrade list. This code
+	-- assumes that the new upgrade inventory size is at least 2.
+	if inv:get_size("upgrade1") > 0 then
+		assert(new_inv_size >= 2)
+		local upg1 = "upgrade1"
+		local upg2 = "upgrade2"
+		local new_list = "upgrades"
+		inv:set_size(new_list, new_inv_size)
+		local stack1 = inv:get_stack(upg1, 1)
+		local stack2 = inv:get_stack(upg2, 1)
+		if stack1 and stack1:get_count() > 0 then
+			inv:set_stack(new_list, 1, stack1)
+			inv:remove_item(upg1, stack1)
+		end
+		if stack2 and stack2:get_count() > 0 then
+			inv:set_stack(new_list, 2, stack2)
+			inv:remove_item(upg2, stack2)
+		end
+		-- Update the formspec.
+		meta:set_string("formspec", new_formspec)
+		inv:set_size(upg1, 0)
+		inv:set_size(upg2, 0)
 	end
-
-	if upg_item2 == "technic:control_logic_unit" then
-		tube_upgrade = tube_upgrade + 1
-	elseif  upg_item2 == "technic:battery" then
-		EU_upgrade = EU_upgrade + 1
-	end
-
-	return EU_upgrade, tube_upgrade
 end
 
--- handles the machine upgrades when set or removed
-local function on_machine_upgrade(meta, stack)
-	local stack_name = stack:get_name()
-	if stack_name == "default:chest" then
-		meta:set_int("public", 1)
-		return 1
-	elseif stack_name ~= "technic:control_logic_unit"
-	   and stack_name ~= "technic:battery" then
-		return 0
-	end
-	return 1
-end
 
--- something is about to be removed
-local function on_machine_downgrade(meta, stack, list)
-	if stack:get_name() == "default:chest" then
-		local inv = meta:get_inventory()
-		local upg1, upg2 = inv:get_stack("upgrade1", 1), inv:get_stack("upgrade2", 1)
 
-		-- only set 0 if theres not another chest in the other list too
-		if (not upg1 or not upg2 or upg1:get_name() ~= upg2:get_name()) then
-			meta:set_int("public", 0)
+-- Calculates the number & type of machine upgrades.
+function technic.handle_machine_upgrades(meta)
+	local inv = meta:get_inventory()
+	local clu = "technic:control_logic_unit"
+	local bat = "technic:battery"
+	local bat_upgrades = 0
+	local clu_upgrades = 0
+	local upgrade_list = "upgrades"
+	local num_upgrade_slots = inv:get_size(upgrade_list)
+
+	for i = 1, num_upgrade_slots, 1 do
+		local stack = inv:get_stack(upgrade_list, i)
+		if stack then
+			local item = stack:get_name()
+			-- Assume that each inv slot cannot have more than 1 upgrade item.
+			if item == bat then bat_upgrades = bat_upgrades + 1 end
+			if item == clu then clu_upgrades = clu_upgrades + 1 end
 		end
 	end
-	return 1
+
+	return bat_upgrades, clu_upgrades
 end
 
 
+
+-- Machine upgrade callback. Called when something is about to be added. Returns
+-- 'true' if the upgrade can be added, 'false' if not.
+local function on_machine_upgrade(player, meta, to_index, stack)
+	local clu = "technic:control_logic_unit"
+	local bat = "technic:battery"
+	local chest = "default:chest"
+	local player_name = player:get_player_name()
+	local inv = meta:get_inventory()
+
+	local item = stack:get_name()
+	if item == chest then
+		meta:set_int("public", 1)
+		return true
+	elseif item == clu then 
+		return true
+	elseif item == bat then 
+		return true
+	end
+
+	minetest.chat_send_player(player_name, S("That is not a valid upgrade item!"))
+	return false
+end
+
+
+
+-- Machine downgrade callback. Called just before something is removed.
+local function on_machine_downgrade(player, meta, from_index, stack)
+	local chest = "default:chest"
+	if stack:get_name() == chest then
+		local inv = meta:get_inventory()
+
+		local upgrade_list = "upgrades"
+		local num_upgrade_slots = inv:get_size(upgrade_list)
+
+		-- Check if any of the upgrade slots contain a chest.
+		local has_chest = false
+		for i = 1, num_upgrade_slots, 1 do
+			if i ~= from_index then -- Skip the chest that's about to be removed.
+				local stack = inv:get_stack(upgrade_list, i)
+				if stack then
+					local item = stack:get_name()
+					if item == chest then 
+						has_chest = true
+						break -- If one chest is found, we don't need to look for more.
+					end
+				end
+			end
+		end
+
+		-- If none of the upgrade slots contains a chest, the machine is no longer
+		-- publicly accessible.
+		if has_chest == false then meta:set_int("public", 0) end
+	end
+end
+
+
+
 function technic.send_items(pos, x_velocity, z_velocity, output_name, item_count)
 	-- Send items on their way in the pipe system.
 	if output_name == nil then
@@ -136,8 +205,8 @@ function technic.handle_machine_pipeworks(pos, tube_upgrade, send_function, item
 	local eject_count = meta:get_int("eject_count") + items_processed_this_cycle
 	meta:set_int("eject_count", eject_count)
 
-	local tube_upgrade_max = 2
-	local norm_tube_upgrade = tube_upgrade / tube_upgrade_max
+	local num_upgrade_slots = inv:get_size("upgrades")
+	local norm_tube_upgrade = technic.normalize_value(tube_upgrade, 0, num_upgrade_slots)
 	local stack_size = 11
 	local tube_time = meta:get_int("tube_time") + 1
 
@@ -174,10 +243,12 @@ end
 function technic.machine_can_dig(pos, player)
 	local meta = minetest.get_meta(pos)
 	local inv = meta:get_inventory()
+
 	if not inv:is_empty("src") or not inv:is_empty("dst") then
 		if player then
-			minetest.chat_send_player(player:get_player_name(),
-				S("Machine cannot be removed because it is not empty"))
+			local name = player:get_player_name()
+			minetest.chat_send_player(
+				name, S("Machine cannot be removed because it is not empty"))
 		end
 		return false
 	end
@@ -187,16 +258,15 @@ end
 
 function technic.machine_after_dig_node(pos, oldnode, oldmetadata, player)
 	if oldmetadata.inventory then
-		if oldmetadata.inventory.upgrade1 and oldmetadata.inventory.upgrade1[1] then
-			local stack = ItemStack(oldmetadata.inventory.upgrade1[1])
-			if not stack:is_empty() then
-				minetest.item_drop(stack, "", pos)
-			end
-		end
-		if oldmetadata.inventory.upgrade2 and oldmetadata.inventory.upgrade2[1] then
-			local stack = ItemStack(oldmetadata.inventory.upgrade2[1])
-			if not stack:is_empty() then
-				minetest.item_drop(stack, "", pos)
+		if oldmetadata.inventory.upgrades then
+			local num_upgrade_slots = #(oldmetadata.inventory.upgrades)
+			for i = 1, num_upgrade_slots, 1 do
+				if oldmetadata.inventory.upgrades[i] then
+					local stack = ItemStack(oldmetadata.inventory.upgrades[i])
+					if not stack:is_empty() then
+						minetest.add_item(pos, stack)
+					end
+				end
 			end
 		end
 	end
@@ -206,42 +276,52 @@ function technic.machine_after_dig_node(pos, oldnode, oldmetadata, player)
 	end
 end
 
-local function inv_change(pos, player, count, from_list, to_list, stack)
-	local playername = player:get_player_name()
-	local meta = minetest.get_meta(pos);
-	local public = (meta:get_int("public") == 1)
-	local to_upgrade = to_list == "upgrade1" or to_list == "upgrade2"
-	local from_upgrade = from_list == "upgrade1" or from_list == "upgrade2"
 
-	if (not public or to_upgrade or from_upgrade) and minetest.is_protected(pos, playername) then
-		minetest.chat_send_player(playername, S("Inventory move disallowed due to protection"))
+
+local function inv_change(pos, player, count, from_list, from_index, to_list, to_index, stack)
+	local player_name = player:get_player_name()
+	local meta = minetest.get_meta(pos)
+	local public = (meta:get_int("public") == 1)
+	local is_upgrade = (to_list == "upgrades")
+	local is_downgrade = (from_list == "upgrades")
+
+	if (not public or is_upgrade or is_downgrade) and minetest.is_protected(pos, player_name) then
+		minetest.chat_send_player(player_name, S("Inventory move disallowed due to protection"))
 		return 0
 	end
-	if to_upgrade then
-		-- only place a single item into it, if it's empty
-		local empty = meta:get_inventory():is_empty(to_list)
-		if empty then
-			return on_machine_upgrade(meta, stack)
+
+	if is_upgrade then
+		local previous_stack = meta:get_inventory():get_stack("upgrades", to_index)
+		-- Only place a single item into the upgrade slot, if it is empty.
+		if previous_stack:get_count() == 0 then
+			if on_machine_upgrade(player, meta, to_index, stack) then
+				count = 1
+			else
+				count = 0
+			end
+		else
+			count = 0
 		end
-		return 0
-	elseif from_upgrade then
-		-- only called on take (not move)
-		on_machine_downgrade(meta, stack, from_list)
+	elseif is_downgrade then
+		-- Only called on take (not move).
+		on_machine_downgrade(player, meta, from_index, stack)
 	end
+
 	return count
 end
 
-function technic.machine_inventory_put(pos, listname, index, stack, player)
-	return inv_change(pos, player, stack:get_count(), nil, listname, stack)
+
+
+function technic.machine_inventory_put(pos, to_list, to_index, stack, player)
+	return inv_change(pos, player, stack:get_count(), nil, nil, to_list, to_index, stack)
 end
 
-function technic.machine_inventory_take(pos, listname, index, stack, player)
-	return inv_change(pos, player, stack:get_count(), listname, nil, stack)
+function technic.machine_inventory_take(pos, from_list, from_index, stack, player)
+	return inv_change(pos, player, stack:get_count(), from_list, from_index, nil, nil, stack)
 end
 
-function technic.machine_inventory_move(pos, from_list, from_index,
-		to_list, to_index, count, player)
+function technic.machine_inventory_move(pos, from_list, from_index, to_list, to_index, count, player)
 	local stack = minetest.get_meta(pos):get_inventory():get_stack(from_list, from_index)
-	return inv_change(pos, player, count, from_list, to_list, stack)
+	return inv_change(pos, player, count, from_list, from_index, to_list, to_index, stack)
 end
 
diff --git a/technic/machines/register/machine_base.lua b/technic/machines/register/machine_base.lua
index 361f491..9062c42 100644
--- a/technic/machines/register/machine_base.lua
+++ b/technic/machines/register/machine_base.lua
@@ -26,6 +26,7 @@ function technic.register_base_machine(data)
 	local machine_desc = data.machine_desc
 	local tier = data.tier
 	local ltier = string.lower(tier)
+	local num_upgrade_slots = data.upgrade_slots or 2
 
 	local groups = {cracky = 2, technic_machine = 1}
 	local active_groups = {cracky = 2, technic_machine = 1, not_in_creative_inventory = 1}
@@ -36,7 +37,6 @@ function technic.register_base_machine(data)
 		active_groups.tubedevice_receiver = 1
 	end
 
-
 	local formspec =
 		"invsize[8,9;]"..
 		"list[current_name;src;"..(4-input_size)..",1;"..input_size..",1;]"..
@@ -49,12 +49,9 @@ function technic.register_base_machine(data)
 		"listring[current_player;main]"
 	if data.upgrade then
 		formspec = formspec..
-			"list[current_name;upgrade1;1,3;1,1;]"..
-			"list[current_name;upgrade2;2,3;1,1;]"..
-			"label[1,4;"..S("Upgrade Slots").."]"..
-			"listring[current_name;upgrade1]"..
-			"listring[current_player;main]"..
-			"listring[current_name;upgrade2]"..
+			"list[current_name;upgrades;0,3;"..num_upgrade_slots..",1;]"..
+			"label[0,4;"..S("Upgrade Slots").."]"..
+			"listring[current_name;upgrades]"..
 			"listring[current_player;main]"
 	end
 
@@ -67,19 +64,31 @@ function technic.register_base_machine(data)
 		local machine_node      = "technic:"..ltier.."_"..machine_name
 		local machine_demand    = data.demand
 
+		-- This is the percentage by which the base demand may be reduced by a
+		-- complete complement of battery upgrades. Fewer battery upgrades than the
+		-- maximum possible will reduce the total demand by less than this.
+		local machine_demand_reduction_factor = data.demand_reduction_factor or 0.0
+
 		-- Setup meta data if it does not exist.
 		if not eu_input then
-			meta:set_int(tier.."_EU_demand", machine_demand[1])
+			meta:set_int(tier.."_EU_demand", machine_demand)
 			meta:set_int(tier.."_EU_input", 0)
 			return
 		end
 
+		-- Do compatibility updates if needed.
+		technic.transfer_upgrades_to_new_upgrade_inventory(meta, formspec, num_upgrade_slots)
+
 		local EU_upgrade, tube_upgrade = 0, 0
 		if data.upgrade then
 			EU_upgrade, tube_upgrade = technic.handle_machine_upgrades(meta)
 		end
 
-		local powered = eu_input >= machine_demand[EU_upgrade+1]
+		-- Calculate the required EUs based on the normalized number of battery upgrades.
+		local norm_eu_upgrade = technic.normalize_value(EU_upgrade, 0, num_upgrade_slots)
+		local total_required_power = machine_demand - ((machine_demand * machine_demand_reduction_factor) * norm_eu_upgrade)
+
+		local powered = eu_input >= total_required_power
 		if powered then
 			meta:set_int("src_time", meta:get_int("src_time") + round(data.speed*10))
 		end
@@ -95,7 +104,7 @@ function technic.register_base_machine(data)
 				meta:set_int("src_time", 0)
 				break
 			end
-			meta:set_int(tier.."_EU_demand", machine_demand[EU_upgrade+1])
+			meta:set_int(tier.."_EU_demand", total_required_power)
 			technic.swap_node(pos, machine_node.."_active")
 			meta:set_string("infotext", S("%s Active"):format(machine_desc_tier))
 			if meta:get_int("src_time") < round(result.time*10) then
@@ -158,8 +167,7 @@ function technic.register_base_machine(data)
 			local inv = meta:get_inventory()
 			inv:set_size("src", input_size)
 			inv:set_size("dst", 4)
-			inv:set_size("upgrade1", 1)
-			inv:set_size("upgrade2", 1)
+			inv:set_size("upgrades", num_upgrade_slots)
 		end,
 		can_dig = technic.machine_can_dig,
 		allow_metadata_inventory_put = technic.machine_inventory_put,
diff --git a/wrench/technic.lua b/wrench/technic.lua
index c404180..22460df 100644
--- a/wrench/technic.lua
+++ b/wrench/technic.lua
@@ -75,7 +75,7 @@ wrench:register_node("technic:lv_electric_furnace_active", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_electric_furnace", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -84,7 +84,7 @@ wrench:register_node("technic:mv_electric_furnace", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_electric_furnace_active", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -127,7 +127,7 @@ wrench:register_node("technic:alloy_furnace_active", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_alloy_furnace", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -136,7 +136,7 @@ wrench:register_node("technic:mv_alloy_furnace", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_alloy_furnace_active", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -145,7 +145,7 @@ wrench:register_node("technic:mv_alloy_furnace_active", {
 		src_time = INT},
 })
 wrench:register_node("technic:tool_workshop", {
-	lists = {"src", "upgrade1", "upgrade2"},
+	lists = {"src", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -169,7 +169,7 @@ wrench:register_node("technic:grinder_active", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_grinder", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -178,7 +178,7 @@ wrench:register_node("technic:mv_grinder", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_grinder_active", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -203,7 +203,7 @@ wrench:register_node("technic:extractor_active", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_extractor", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -212,7 +212,7 @@ wrench:register_node("technic:mv_extractor", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_extractor_active", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -237,7 +237,7 @@ wrench:register_node("technic:compressor_active", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_compressor", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -246,7 +246,7 @@ wrench:register_node("technic:mv_compressor", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_compressor_active", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -273,7 +273,7 @@ wrench:register_node("technic:cnc_active", {
 		cnc_product = STRING},
 })
 wrench:register_node("technic:mv_centrifuge", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,
@@ -282,7 +282,7 @@ wrench:register_node("technic:mv_centrifuge", {
 		src_time = INT},
 })
 wrench:register_node("technic:mv_centrifuge_active", {
-	lists = {"src", "dst", "upgrade1", "upgrade2"},
+	lists = {"src", "dst", "upgrade1", "upgrade2", "upgrades"},
 	metas = {infotext = STRING,
 		formspec = STRING,
 		MV_EU_demand = INT,