Introduce auxiliary functions to change craft amount

In the next commits these will be used in place of the hardcoded
overrides.

redefinitions.lua

@@ -5,7 +5,72 @@ Copyright © 2011-2020 Hugo Locurcio and contributors.
 Licensed under the zlib license. See LICENSE.md for more information.
 --]]
 
--- Redefinitions of some default crafting recipes:
+-- Redefine some of the default crafting recipes to be more productive
+
+-- Auxiliary function: take a recipe as returned by get_all_craft_recipes
+-- and turn it into a table that can be used to clear a craft or declare a new one
+local reconstruct_internal_craft = function(recipe)
+	local recp = {
+		{ "", "", "" },
+		{ "", "", "" },
+		{ "", "", "" },
+	}
+	for idx, item in pairs(recipe.items) do
+		local row = math.ceil(idx / recipe.width)
+		local col = idx - (row-1)*recipe.width
+		recp[row][col] = item
+	end
+	return recp
+end
+
+-- Change the amount produced by recipe by apply func to the old amount
+local change_recipe_amount = function(product, recipe, func)
+	local recp = reconstruct_internal_craft(recipe)
+
+	local oldamount = tonumber(recipe.output:match(" [0-9]+$") or "1")
+
+	local newamount = func(oldamount)
+
+	-- remove old crafting recipe
+	local redo = { recipe = recp }
+	minetest.clear_craft(redo)
+
+	-- new output
+	redo.output = ("%s %d"):format(product, newamount)
+	minetest.register_craft(redo)
+
+	minetest.log(("moreblocks recipe for %s production: %d => %d"):format(product, oldamount, newamount))
+end
+
+local increase_craft_production = function(product, func)
+	local recipes = minetest.get_all_craft_recipes(product)
+	for _, r in pairs(recipes) do
+		if r.type == "normal" or r.method == "normal" then
+			minetest.log(dump(r))
+			change_recipe_amount(product, r, func)
+		end
+	end
+end
+
+-- Increase the crafting production according to the rules from the table, which is in the form:
+-- {
+--   { detector, amount changing function }
+--   { detector, amount changing function }
+-- }
+-- TODO: consider exporting this function to other mods
+local increase_craft_production_table = function(map_table)
+	for product, _ in pairs(minetest.registered_items) do
+		for _, tab in pairs(map_table) do
+			local detector = tab[1]
+			local func = tab[2]
+			if detector(product) then
+				increase_craft_production(product, func)
+				-- only apply one boost
+				break
+			end
+		end
+	end
+end
 
 -- Signs: +1
 minetest.clear_craft({