elepower/elepower_machines/machines/wind_turbine.lua

local function get_formspec_default(power, state)
	return "size[8,8.5]"..
		default.gui_bg..
		default.gui_bg_img..
		default.gui_slots..
		ele.formspec.power_meter(power)..
		ele.formspec.state_switcher(7, 0, state)..
		"list[current_player;main;0,4.25;8,1;]"..
		"list[current_player;main;0,5.5;8,3;8]"..
		default.get_hotbar_bg(0, 4.25)
end

-- Primitive wind checking function
elepm.wind_height_constant = 20
function elepm.wind_check(pos)
	if pos.y < 10 then
		return 0
	end
	
	local power = math.ceil(pos.y / elepm.wind_height_constant)
	
	if math.floor(pos.y / elepm.wind_height_constant) > 25 then
		power = 25
	end
	
	return power
end

-- A generator that creates power using altitude
function ele.register_wind_generator(nodename, nodedef)
	-- Allow for custom formspec
	local get_formspec = get_formspec_default
	if nodedef.get_formspec then
		get_formspec = nodedef.get_formspec
		nodedef.get_formspec = nil
	end

	local defaults = {
		groups = {
			ele_provider = 1,
			oddly_breakable_by_hand = 1,
			wind_generator = 1,
		},
		tube = false,
		paramtype2 = 0,
		on_timer = function (pos, elapsed)
			
			local refresh  = false
			local meta     = minetest.get_meta(pos)
			
			local capacity   = ele.helpers.get_node_property(meta, pos, "capacity")
			local generation = ele.helpers.get_node_property(meta, pos, "usage")
			local storage    = ele.helpers.get_node_property(meta, pos, "storage")

			local state = meta:get_int("state")
			local is_enabled = ele.helpers.state_enabled(meta, pos, state)

			local pow_buffer = {capacity = capacity, storage = storage, usage = 0}
			local status = "Idle"

			local wind = meta:get_int("wind")

			while true do
				if not is_enabled then
					status = "Off"
					wind = 0
					break
				end

				local multiplier = 1
				local tentpos = vector.subtract(pos, {x=0,y=0,z=1})
				for i, ob in pairs(minetest.get_objects_inside_radius(tentpos, 0.5)) do
					if ob:get_luaentity() and ob:get_luaentity().name == "elepower_machines:wind_turbine_blades" then
						multiplier = 4
						break
					end
				end

				wind = elepm.wind_check(pos) * multiplier
				
				if wind == 0 then
					status = "No wind"
					break
				end

				pow_buffer.usage = wind
				if pow_buffer.storage + pow_buffer.usage > pow_buffer.capacity then
					break
				end

				status = "Active"
				refresh = true

				pow_buffer.storage = pow_buffer.storage + pow_buffer.usage
				break
			end

			meta:set_string("formspec", get_formspec(pow_buffer, state))
			meta:set_string("infotext", ("Wind Turbine %s\n%s"):format(status,
				ele.capacity_text(capacity, pow_buffer.storage)))

			meta:set_int("storage", pow_buffer.storage)
			meta:set_int("wind", wind)

			return refresh
		end,
		on_construct = function (pos)
			local meta = minetest.get_meta(pos)

			local capacity = ele.helpers.get_node_property(meta, pos, "capacity")
			local storage  = ele.helpers.get_node_property(meta, pos, "storage")

			meta:set_string("formspec", get_formspec({capacity = capacity, storage = storage, usage = 0}, 0))
			minetest.get_node_timer(pos):start(1)
		end
	}

	for key,val in pairs(defaults) do
		if not nodedef[key] then
			nodedef[key] = val
		end
	end
	
	ele.register_machine(nodename, nodedef)
end

ele.register_wind_generator("elepower_machines:wind_turbine", {
	description = "Wind Turbine\n(Requires Wind Turbine Blades)",
	tiles = {
		"elepower_machine_top.png", "elepower_machine_base.png", "elepower_machine_side.png",
		"elepower_machine_side.png", "elepower_machine_side.png", "elepower_machine_side.png^elepower_wind_turbine_face.png",
	},
	ele_upgrades = {
		capacitor = {"capacity"},
	}
})

minetest.register_craftitem("elepower_machines:wind_turbine_blades", {
	description = "Wind Turbine Blades (Wooden)\nSneak Right-Click on the Wind Turbine node to place it",
	inventory_image = "elepower_wind_turbine_blades.png",
	on_place = function (itemstack, clicker, pointed_thing)
		local pos = pointed_thing.under
		if pointed_thing.type ~= "node" then return itemstack end

		local node = minetest.get_node(pos)
		if minetest.get_item_group(node.name, "wind_generator") == 0 then
			return itemstack
		end
		local place_at = vector.add(pos, {x = 0, y = 0, z = -1})
		local e = minetest.add_entity(place_at, "elepower_machines:wind_turbine_blades")
		local ent = e:get_luaentity()
		ent.controller = pos
		
		itemstack:take_item(1)
		return itemstack
	end
})

minetest.register_entity("elepower_machines:wind_turbine_blades", {
	initial_properties = {
		hp_max   = 10,
		visual   = "mesh",
		mesh     = "elepower_wind_blades.obj",
		physical = true,
		textures = {"default_wood.png"},
		backface_culling = false,
		visual_size = {x = 10, y = 10},
	},
	timer = 0,
	wind = false,

	on_step = function (self, dt)
		if self.wind then
			local rot = self.object:get_rotation()
			self.object:set_rotation({x = 0, y = 0, z = rot.z + 0.02 * math.pi})
		end

		-- Wind check timer
		self.timer = self.timer + 1
		
		if self.timer < 100 then
			return self
		end
		self.timer = 0
		
		--controller pos always +1 z (note this can be made more robust)
		local controller = vector.add(self.object:get_pos(), {x = 0, y = 0, z = 1})
		local c_meta = minetest.get_meta(controller)
		
		-- check controller timer (already using onstep here so saves an extra one)
		if not minetest.get_node_timer(controller):is_started() then
				minetest.get_node_timer(controller):start(1)
		end
		
		if c_meta and c_meta:get_int("wind") > 0 then
			self.wind = true
		else
			self.wind = false
		end
		
	end,
	on_punch = function (self, puncher, time_from_last_punch, tool_capabilities, dir)
		local itm = ItemStack("elepower_machines:wind_turbine_blades")
		if not puncher or puncher == "" or puncher:get_player_name() == "" then return self end
		local inv = puncher:get_inventory()
		if inv:room_for_item("main", itm) then
			inv:add_item("main", itm)
		else
			minetest.item_drop(itm, puncher, self.object:get_pos())
		end
		self.object:set_hp(0)
	end
})