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