local entity = minetest.registered_entities["__builtin:falling_node"]



local original_try_place = entity.try_place
local after_land_callbacks = {}

entity.try_place = function (self, bcp, bcn)
	local result = original_try_place(self, bcp, bcn)
	-- `result` will be true if the falling node landed successfully (afaict from reading `/builtin/game/falling.lua` in the minetest source).
	if result then
		-- `bcp` is actually the node 0.7 nodes (rounded) below the falling_node entity.
		-- the vector addition here makes it be the position where the entity itself landed.
		-- if it landed on something layered, this new position might be air when the callbacks are called.
		local pos = bcp + vector.new(0, 1, 0)
		for _, callback in pairs(after_land_callbacks) do
			callback(pos, bcn, self)
		end
	end
	return result
end

function blockgame.register_after_falling_node_lands (callback)
	table.insert(after_land_callbacks, callback)
end

blockgame.register_after_falling_node_lands(function (pos, node)
	local def = minetest.registered_nodes[node.name]

	if type(def.after_landing) == "function" then
		def.after_landing(pos, node)
	end
end)



local original_on_step = entity.on_step
local on_step_callbacks = {}

entity.on_step = function (self, dtime, moveresult)
	local result = original_on_step(self, dtime, moveresult)
	for _, callback in pairs(on_step_callbacks) do
		callback(self, dtime, moveresult)
	end
	return result
end

function blockgame.register_on_falling_node_step (callback)
	table.insert(on_step_callbacks, callback)
end

-- keep track of velocity a falling_node had before landing
-- so that code hooked into the landing can check "how fast was this moving?"
blockgame.register_on_falling_node_step(function (entity, delta_time, move_result)
	local velocity = entity.object:get_velocity()

	-- let `previous_velocity` be (0, 0, 0) at the very first step
	if not entity.fall_velocity then
		entity.fall_velocity = vector.new(0, 0, 0)
	end

	-- keep track of moving velocity, not still velocity
	if velocity and (vector.length(velocity) ~= 0) then
		entity.fall_velocity = vector.copy(velocity)
	end

end)