--- Overlap command. Places a specified node on top of 
-- @module worldeditadditions.overlay

function worldedit.ellipsoid(position, radius, target_node, hollow)
	-- position = { x, y, z }
	local hollow_inner_radius = {
		x = radius.x - 1,
		y = radius.y - 1,
		z = radius.z - 1
	}
	
	-- Fetch the nodes in the specified area
	-- OPTIMIZE: We should be able to calculate a more efficient box-area here
	local manip, area = worldedit.manip_helpers.init_radius(position, math.max(radius.x, radius.y, radius.z))
	local data = manip:get_data()
	
	local node_id = minetest.get_content_id(target_node)
	local node_id_air = minetest.get_content_id("air")
	
	local stride_z, stride_y = area.zstride, area.ystride
	
	local count = 0 -- The number of nodes replaced
	
	local idx_z_base = area:index(position.x - radius.x, position.y - radius.y, position.z - radius.z) -- initial z offset
	for z = -radius.z, radius.z do
		
		local idx_y_base = idx_z_base
		for y = -radius.y, radius.y do
			
			local i = idx_y_base
			for x = -radius.x, radius.x do
				
				-- If we're inside the ellipse, then fill it in
				local x_comp, y_comp, z_comp = x/radius.x, y/radius.y, z/radius.z
				local ellipsoid_dist = x_comp*x_comp + y_comp*y_comp + z_comp*z_comp
				if ellipsoid_dist <= 1 then
					local place_ok = not hollow;
					
					if not place_ok then
						-- It must be hollow! Do some additional calculations.
						local hx_comp = x/hollow_inner_radius.x
						local hy_comp = y/hollow_inner_radius.y
						local hz_comp = z/hollow_inner_radius.z
						
						-- It's only ok to place it if it's outside our inner ellipse
						place_ok = hx_comp*hx_comp + hy_comp*hy_comp + hz_comp*hz_comp >= 1
					end
					
					if place_ok then
						data[i] = node_id
						count = count + 1
					end
				end
				
				
				i = i + 1
			end
			idx_y_base = idx_y_base + stride_y
			
		end
		idx_z_base = idx_z_base + stride_z
		
	end
	
	
	-- Save the modified nodes back to disk & return
	worldedit.manip_helpers.finish(manip, data)
	
	return count
end
