data-fns/src/lib/palindrome.ts

This library provides utility functions for working with array data that are useful in many contexts, including creative coding. It offers generic functions that perform common operations such as offsetting an array, generating an array based on a callbac

/**
 * Maps an index to a palindrome pattern.
 * @param index The original index.
 * @param length The length of the sequence.
 * @returns The mapped index in the palindrome pattern.
 * @example
 * const length = 5
 * const indexes = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
 * indexes.map((index) => palindrome(index, length))
 * // Returns [0, 1, 2, 1, 0, 1, 2, 1, 0, 1]
 */
export const palindrome = (index: number, length: number): number => {
  // Save the length of the sequence in a variable
  const arraySize = length

  // If the sequence has only one element, return 0
  if (arraySize === 1) {
    return 0
  }

  // Calculate the mapped index based on the palindrome pattern
  const normalizedIndex = index % (2 * arraySize - 2)
  const id = normalizedIndex >= 0 ? normalizedIndex : 2 * arraySize - 2 + normalizedIndex

  if (id < arraySize) {
    return Math.abs(id)
  } else {
    return 2 * arraySize - id - 2
  }
}