local heightmap = require "lib.heightmap"
local lume = require "lib.lume"

local biomes = {
  -- [5] = {
  --   name = "ocean",
  --   altitude = {min = 0, max = 0.2}, -- bottom of world is the only part that matters
  --   temperature = {min = 0, max = 1},
  --   humidity = {min = 0, max = 1},
  --   color = {0, 0, 0.67, 1},
  -- },
  -- [6] = {
  --   name = "beach",
  --   altitude = {min = 0.2, max = 0.205}, -- just above ocean
  --   temperature = {min = 0, max = 1},
  --   humidity = {min = 0, max = 0.8}, -- excluding upper humidity for swamp
  --   color = {1, 1, 0.33, 1}, -- brighter yellow to distinguish from sand
  -- },
  -- [8] = {
  --   name = "swamp", -- fun idea, but generates between ocean and water too often?
  --   altitude = {min = 0, max = 1},
  --   temperature = {min = 0.5, max = 1},
  --   humidity = {min = 0.95, max = 1},
  --   color = {0, 0.5, 0.33, 1},
  -- },
  -- [10] = {
  --   name = "water",
  --   altitude = {min = 0, max = 0.9}, -- top excluded because it should've gone downhill
  --   temperature = {min = 0.1, max = 0.9}, -- bottom should be ice, top should evaporate
  --   humidity = {min = 0.8, max = 1}, -- only the wettest places
  --   color = {0, 0, 1, 1},
  -- },
  -- [20] = {
  --   name = "sand",
  --   altitude = {min = 0.2, max = 0.9}, -- top falls down, bottom is underwater
  --   temperature = {min = 0, max = 1},
  --   humidity = {min = 0, max = 0.2}, -- only where dry makes more sense for a desert
  --   color = {1, 1, 0, 1},
  -- },
  -- [30] = {
  --   name = "grass",
  --   altitude = {min = 0.3, max = 0.9}, -- top of the world not enough air, bottom too wet / leaving space for others
  --   temperature = {min = 0.2, max = 0.8}, -- not very sensitive to temperature
  --   humidity = {min = 0.2, max = 0.6}, -- not very sensitive to humidity; but excluded from the worst
  --   color = {0, 1, 0, 1},
  -- },
  -- [40] = {
  --   name = "trees",
  --   altitude = {min = 0.4, max = 0.7}, -- more sensitive than grass
  --   temperature = {min = 0, max = 0.7},
  --   humidity = {min = 0.3, max = 0.8}, -- these are not desert trees, they need more water
  --   color = {0, 0.67, 0, 1},
  -- },
  -- [60] = {
  --   name = "stone",
  --   altitude = {min = 0, max = 1},
  --   temperature = {min = 0, max = 1},
  --   humidity = {min = 0, max = 1},
  --   color = {0.67, 0.67, 0.67, 1},
  -- },
  -- [50] = {
  --   name = "ice",
  --   altitude = {min = 0, max = 1},
  --   temperature = {min = 0, max = 0.01},
  --   humidity = {min = 0.2, max = 1},
  --   color = {1, 1, 1, 1},
  -- },
  [900] = {
    name = "deep ocean",
    altitude = {min = -math.huge, max = -5000},
    temperature = {min = -math.huge, max = math.huge},
    humidity = {min = -math.huge, max = math.huge},
    color = {0, 0, 0.25, 1},
  },
  [1000] = {
    name = "ocean (definition, 0 meters)",
    altitude = {min = -math.huge, max = 0},
    temperature = {min = -math.huge, max = math.huge},
    humidity = {min = -math.huge, max = math.huge},
    color = {0, 0, 0.5, 1},
  },
  [2000] = {
    name = "snowline (middle estimate)",
    altitude = {min = 4000, max = math.huge},
    temperature = {min = -math.huge, max = math.huge},
    humidity = {min = -math.huge, max = math.huge},
    color = {1, 1, 1, 1},
  },
  [2100] = {
    name = "alpine zone",
    altitude = {min = 3500, max = math.huge},
    temperature = {min = -math.huge, max = math.huge},
    humidity = {min = -math.huge, max = math.huge},
    color = {0.8, 0.8, 0.8, 1},
  },
  [2200] = {
    name = "subalpine zone",
    altitude = {min = 3000, max = math.huge},
    temperature = {min = -math.huge, max = math.huge},
    humidity = {min = -math.huge, max = math.huge},
    color = {0.67, 0.67, 0.67, 1},
  },
  [2300] = {
    name = "montane zone",
    altitude = {min = 2500, max = math.huge},
    temperature = {min = -math.huge, max = math.huge},
    humidity = {min = -math.huge, max = math.huge},
    color = {0.67, 0.67, 0.5, 1},
  },
}

local function generate()
  local map = {}

  map.size = 500
  map.tile_size = 1
  map.altitude = heightmap.create(map.size, map.size, 0, 1) -- meters
  map.temperature = heightmap.create(map.size, map.size, -89.2, 56.7) -- celsius
  map.humidity = heightmap.create(map.size, map.size, 18, 3240) -- millimeters rainfall

  -- local function earthlike_altitude_adjustment(altitude)
  --   -- max too low, min too high, too much ocean
  --   return 6099 - 114909 * altitude + 830891 * altitude^2 - 2.72e6 * altitude^3 + 4.19e6 * altitude^4 - 3.02e6 * altitude^5 + 815866 * altitude^6
  -- end
  local function earthlike_altitude_adjustment(altitude)
    -- good oceans, too much high altitude
    return -10948 + 101018 * altitude - 643382 * altitude^2 + 2.17e6 * altitude^3 - 3.62e6 * altitude^4 + 2.87e6 * altitude^5 -852042 * altitude^6
  end
  -- local function earthlike_altitude_adjustment(altitude)
  --   -- only creates ocean (wtf)
  --   return -10851 + 151279 * altitude - 1.14e6 * altitude^2 +3.84e6 * altitude^3 -6.11e6 * altitude^4 +4.48e6 * altitude^5 - 1.21e6 * altitude^6
  -- end
  local min, max = math.huge, -math.huge
  for x = 0, map.size do
    for y = 0, map.size do
      local value = earthlike_altitude_adjustment(map.altitude[x][y])
      if value > max then max = value end
      if value < min then min = value end
      map.altitude[x][y] = value
    end
  end
  print("Altitude", "Min: ", min, "Max:", max)

  -- planetizer!
  local biome_order = {}
  for order in pairs(biomes) do
    biome_order[#biome_order + 1] = order
  end
  table.sort(biome_order)

  map.terrain = {w = map.size, h = map.size}
  local radius = (map.size / 2)^2
  for x = 0, map.size do
    map.terrain[x] = {}
    for y = 0, map.size do
      if lume.distance(x, y, map.size / 2, map.size / 2, true) < radius then
        -- for _, biome in ipairs(biomes) do
        for _, order in ipairs(biome_order) do
          local biome = biomes[order]
          local altitude = map.altitude[x][y]
          if altitude >= biome.altitude.min and altitude <= biome.altitude.max then
            local temperature = map.temperature[x][y]
            if temperature >= biome.temperature.min and temperature <= biome.temperature.max then
              local humidity = map.humidity[x][y]
              if humidity >= biome.humidity.min and humidity <= biome.humidity.max then
                map.terrain[x][y] = biome.color
                break
              end
            end
          end
        end
      end
    end
  end

  return map
end

return {
  generate = generate,
}