local REALM_START = vector.new(-500, -500, -500)
local REALM_END = vector.new(500, 500, 500)

local function intersection(min, max, b, c)
    return min.x < c.x and max.x > b.x and
           min.y < c.y and max.y > b.y and
           min.z < c.z and max.z > b.z
end

local vm_data = {}

local np_surface = {
    offset = 0,
    scale = 1,
    spread = {x = 100, y = 100, z = 100},
    seed = 12345,
    octaves = 4,
    persist = 0.6
}
local n_surface = {}

local np_thickness = {
    offset = 0,
    scale = 1,
    spread = {x = 250, y = 250, z = 250},
    seed = 3579044,
    octaves = 4,
    persist = 0.6
}
local n_thickness = {}


local c_chest = minetest.get_content_id("chest_with_everything:chest")

local c_air = minetest.get_content_id("air")
local c_stone = minetest.get_content_id("stone")
minetest.register_on_generated(function(vm, min, max)
    -- AABB intersection, to determine whether this block should be considered for this mapgen.
    if not intersection(min, max, REALM_START, REALM_END) then return end
    local va = VoxelArea(vm:get_emerged_area())
    
    local sides2d = {x = max.x - min.x + 1, y = max.z - min.z + 1}
    local surface = minetest.get_perlin_map(np_surface, sides2d)
    surface:get_2d_map_flat({x = min.x, y = min.z}, n_surface)

    local thickness = minetest.get_perlin_map(np_thickness, sides2d)
    thickness:get_2d_map_flat({x = min.x, y = min.z}, n_thickness)
    
    vm:get_data(vm_data)
    local ni = 1
    for z = min.z, max.z do
        for x = min.x, max.x do
            local r = math.sqrt(x *x + z *z)
            local bottom = -(3 +n_thickness[ni] *5 +((1 -(r /100))^0.5 *50))
            local top = (n_surface[ni] +1) *8 *(1 -(math.max(0, r -90) /10))^0.5
            
            for y = min.y, max.y do
                if y > bottom and y < top then
                    local vi = va:index(x, y, z)
                    
                    vm_data[vi] = c_stone
                end
                if x == 0 and z == 0 and y == math.round(top) then
                    local vi = va:index(x, y, z)
                    vm_data[vi] = c_chest
                end
            end
            ni = ni +1
        end
    end
    vm:set_data(vm_data)
end)