ValueScript/valuescript_vm/src/helpers.rs

use crate::vs_value::{Val, ValTrait};

pub fn to_wrapping_index(index: Option<&Val>, len: usize) -> Option<usize> {
  let unchecked = match index {
    None => {
      return None;
    }
    Some(i) => to_unchecked_wrapping_index(i, len),
  };

  if unchecked < 0 || unchecked as usize >= len {
    return None;
  }

  Some(unchecked as usize)
}

pub fn to_wrapping_index_clamped(index: &Val, len: usize) -> isize {
  let wrapping_index = to_unchecked_wrapping_index(index, len);

  if wrapping_index < 0 {
    return 0;
  }

  if wrapping_index > len as isize {
    // len-1 would be a mistake. The end of the array is a meaningful index even
    // though there is no data there.
    return len as isize;
  }

  wrapping_index
}

pub fn to_unchecked_wrapping_index(index: &Val, len: usize) -> isize {
  let index_num = index.to_number();

  let mut floored_index = index_num.trunc();
  let f64_len = len as f64;

  if floored_index < 0_f64 {
    floored_index += f64_len;
  }

  // TODO: Investigate potential pitfalls for arrays with length exceeding max
  // isize.
  floored_index as isize
}