local noise = require("noise")
local tne = noise.to_noise_expression
local litexp = noise.literal_expression

local seed1 = 1234
local pi_over_3 = tne(math.pi)/3

-- enemy_base_border_width gives the width of the border in which probability ramps up from 0 to 1.
-- i.e. slope = 1 / border_width, and height = radius / border_width
-- In practice, a probabilty of about 1/9 will result in a solid carpet of biter bases,
-- which is why this border width is so high (ignoring blobbiness, most of the inner part of the 'border' would be solid biter bases)
local enemy_base_border_width = 9

-- Spots per square meter (should be a very small fraction):
local frequency_expression = noise.max(0, noise.var("enemy-base-frequency"))
local spot_radius_expression = noise.max(0, noise.var("enemy-base-radius"))
-- multiply by spot_radius_expression to keep slope constant:
local spot_height_expression = spot_radius_expression / enemy_base_border_width
local spot_quantity_expression = pi_over_3 * spot_radius_expression * spot_radius_expression * spot_height_expression
-- spot_quantity_expression = noise.compile_time_log("Spot quantity: ", spot_quantity_expression)
local density_expression = spot_quantity_expression * frequency_expression
-- density_expression = noise.compile_time_log("Density: ", density_expression)

local basement_value = -1000

local spots = tne{
  type = "function-application",
  function_name = "spot-noise",
  arguments = {
    x = noise.var("x"),
    y = noise.var("y"),
    seed0 = noise.var("map_seed"),
    seed1 = tne(seed1),
    region_size = tne(1024),
    candidate_point_count = tne(4),
    suggested_minimum_candidate_point_spacing = tne(512),
    density_expression = litexp(pi_over_3 * 256 * 256 * 256 / 8),
    -- litexp(density_expression), -- low-frequency noise evaluate for an entire region
    spot_quantity_expression = litexp(pi_over_3 * 256 * 256 * 256 / 8),
    --litexp(spot_quantity_expression), -- used to figure out where spots go
    hard_region_target_quantity = tne(false), -- it's fine for large spots to push region quantity past the target
    spot_radius_expression = litexp(128),
    spot_favorability_expression = litexp(1),
    basement_value = tne(basement_value),
    maximum_spot_basement_radius = tne(256)
  }
}

local jitter = tne{
  type = "function-application",
  function_name = "factorio-basis-noise",
  arguments = {
    x = noise.var("x"),
    y = noise.var("y"),
    seed0 = noise.var("map_seed"), -- i.e. map.seed
    seed1 = tne(123), -- Some random number
    input_scale = noise.var("segmentation_multiplier")/20,
    output_scale = 20/noise.var("segmentation_multiplier")
  }
}

data:extend{
  {
    type = "noise-expression",
    name = "CS-islands",
    intended_property = "elevation",
    expression = noise.define_noise_function(function(x, y, tile, map)
        return tne(spots - 0.1 + jitter / 10000)
        --noise.spots({x=x, y=y, seed0=map.seed, seed1=0})
      end)
  }
}
    
data.raw["map-gen-presets"]["default"].islands = {
  order = "i",
  basic_settings = {
    property_expression_names = {
      elevation = "CS-islands",
    },
    autoplace_controls = {},
    terrain_segmentation = 1,
  }
}