Generate a random value with variety.

Variety.swift

func convert<T: FloatingPoint>(value: T, inRange: ClosedRange<T>, toRange: ClosedRange<T>) -> T {
    let oldRange = inRange.upperBound - inRange.lowerBound
    let newRange = toRange.upperBound - toRange.lowerBound
    return (((value - inRange.lowerBound) * newRange) / oldRange) + toRange.lowerBound
}

/// Variety: [0 - 1]. 0 means no randomisation, 1 means a random value between full range. 
func variety(value: Double, inRange: ClosedRange<Double>, variety: Double) -> Double {
      let normalised = inRange == 0...1 ? value : convert(value: value, inRange: inRange, toRange: 0 ... 1)
      let upper = min(normalised + variety, 1.0)
      let lower = max(normalised - variety, 0.0)
      let rand = Double.random(in: lower ... upper)
      return convert(value: rand, inRange: 0 ... 1, toRange: inRange)
  }