import random
import math
import algorithm

import turtle
import turtle_type
import input_type

proc select*(turtles: var seq[Turtle], input: Input) =
  # sort turtles according to score
  turtles.sort(compareTurtles)

  var scoreSum = 0
  for turtle in turtles:
    scoreSum += turtle.score
  let avgScore = scoreSum div turtles.len()

  var survivors: seq[Turtle] = @[]

  for i in 0..turtles.high():
    let turtle = turtles[i]
    const smoothness = 0.08
    const chanceRandomLive = 0.02
    const chanceRandomDie = 0.0
    let chanceExp = exp(smoothness * float(turtles[i].score - avgScore))
    let chance = chanceRandomLive + (1-chanceRandomDie-chanceRandomLive) * chanceExp / (chanceExp + 1)
    if rand(1.0) < chance:
      survivors.add(turtle)
  
  var i = 0
  while i < turtles.len():
    if turtles[i] notin survivors:
      turtles.del(i)
    else:
      inc i