Show item usages in craft guide

When the craft guide is showing a craft, the output slot is now a button,
which causes the craft guide to show ways in which that output can be
used.  This mirrors the way input slots are buttons that show recipes
for the selected ingredient.  Usages of an item can be iterated through
in the same way as recipes for the item.  This incidentally offers some
ability to retrace one's steps through a crafting chain, without storing
actual history.

register.lua

@@ -169,6 +169,23 @@ local function stack_image_button(x, y, w, h, buttonname_prefix, item)
 			label)
 end
 
+local recipe_text = {
+	recipe = "Recipe",
+	usage = "Usage",
+}
+local no_recipe_text = {
+	recipe = "No recipes",
+	usage = "No usages",
+}
+local role_text = {
+	recipe = "Result",
+	usage = "Ingredient",
+}
+local other_dir = {
+	recipe = "usage",
+	usage = "recipe",
+}
+
 unified_inventory.register_page("craftguide", {
 	get_formspec = function(player)
 		local player_name = player:get_player_name()
@@ -179,36 +196,33 @@ unified_inventory.register_page("craftguide", {
 		local item_name = unified_inventory.current_item[player_name]
 		if not item_name then return {formspec=formspec} end
 
-		formspec = formspec.."background[0,1;8,3;ui_craftguide_form.png]"
-		formspec = formspec.."textarea[0.3,0.6;10,1;;Result: "..minetest.formspec_escape(item_name)..";]"
-		formspec = formspec.."list[detached:"..minetest.formspec_escape(player_name).."craftrecipe;output;6,1;1,1;]"
-		local craftinv = minetest.get_inventory({
-			type = "detached",
-			name = player_name.."craftrecipe"
-		})
-
-		local alternate, alternates, craft, craft_type
-		alternate = unified_inventory.alternate[player_name]
-		local crafts = unified_inventory.crafts_table[item_name]
+		local dir = unified_inventory.current_craft_direction[player_name]
+		local crafts = unified_inventory.crafts_for[dir][item_name]
+		local alternate = unified_inventory.alternate[player_name]
+		local alternates, craft
 		if crafts ~= nil and #crafts > 0 then
 			alternates = #crafts
 			craft = crafts[alternate]
 		end
 
+		formspec = formspec.."background[0,1;8,3;ui_craftguide_form.png]"
+		formspec = formspec.."textarea[0.3,0.6;10,1;;"..minetest.formspec_escape(role_text[dir]..": "..item_name)..";]"
+
 		if not craft then
-			craftinv:set_stack("output", 1, item_name)
-			craft_type = unified_inventory.craft_type_defaults("", {})
-			formspec = formspec.."label[6,3.35;No recipes]"
-			formspec = formspec.."image[4,1;1.1,1.1;ui_no.png]"
+			formspec = formspec.."label[6,3.35;"..minetest.formspec_escape(no_recipe_text[dir]).."]"
+			local no_pos = dir == "recipe" and 4 or 6
+			local item_pos = dir == "recipe" and 6 or 4
+			formspec = formspec.."image["..no_pos..",1;1.1,1.1;ui_no.png]"
+			formspec = formspec..stack_image_button(item_pos, 1, 1.1, 1.1, "item_button_"..other_dir[dir].."_", ItemStack(item_name))
 			return {formspec = formspec}
 		end
 
-		craftinv:set_stack("output", 1, craft.output)
-		craft_type = unified_inventory.registered_craft_types[craft.type] or
+		local craft_type = unified_inventory.registered_craft_types[craft.type] or
 				unified_inventory.craft_type_defaults(craft.type, {})
 		formspec = formspec.."label[6,3.35;Method:]"
 		formspec = formspec.."label[6,3.75;"
 				..minetest.formspec_escape(craft_type.description).."]"
+		formspec = formspec..stack_image_button(6, 1, 1.1, 1.1, "item_button_usage_", ItemStack(craft.output))
 		local display_size = craft_type.dynamic_display_size and craft_type.dynamic_display_size(craft) or { width = craft_type.width, height = craft_type.height }
 		local craft_width = craft_type.get_shaped_craft_width and craft_type.get_shaped_craft_width(craft) or display_size.width
 
@@ -224,7 +238,8 @@ unified_inventory.register_page("craftguide", {
 			if item then
 				formspec = formspec..stack_image_button(
 						xoffset + x, y, 1.1, 1.1,
-						"item_button_", ItemStack(item))
+						"item_button_recipe_",
+						ItemStack(item))
 			else
 				-- Fake buttons just to make grid
 				formspec = formspec.."image_button["
@@ -242,7 +257,7 @@ unified_inventory.register_page("craftguide", {
 		end
 
 		if alternates and alternates > 1 then
-			formspec = formspec.."label[0,2.6;Recipe "
+			formspec = formspec.."label[0,2.6;"..recipe_text[dir].." "
 					..tostring(alternate).." of "
 					..tostring(alternates).."]"
 					.."button[0,3.15;2,1;alternate;Alternate]"
@@ -259,17 +274,13 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 	end
 	if not amount then return end
 	local player_name = player:get_player_name()
-	local recipe_inv = minetest.get_inventory({
-		type="detached",
-		name=player_name.."craftrecipe",
-	})
 
 	local output = unified_inventory.current_item[player_name]
 	if (not output) or (output == "") then return end
 
 	local player_inv = player:get_inventory()
 
-	local crafts = unified_inventory.crafts_table[output]
+	local crafts = unified_inventory.crafts_for[unified_inventory.current_craft_direction[player_name]][output]
 	if (not crafts) or (#crafts == 0) then return end
 
 	local alternate = unified_inventory.alternate[player_name]