type ProdValue = number | string

export function prod(values: ProdValue[] | unknown, start: ProdValue = 1): ProdValue {
  //      discuss at: https://locutus.io/python/prod/
  // parity verified: Python 3.12
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Multiplies all iterable values together and applies the optional start value first.
  //       example 1: prod([2, 3, 4])
  //       returns 1: 24
  //       example 2: prod([], 5)
  //       returns 2: 5
  //       example 3: prod([1.5, 2, 3], 2)
  //       returns 3: 18

  if (!Array.isArray(values)) {
    throw new TypeError('prod(): iterable must be an array')
  }

  let result: ProdValue = start
  for (const value of values) {
    result = multiplyProdValues(result, value)
  }

  return result
}

function multiplyProdValues(left: ProdValue, right: ProdValue): ProdValue {
  if (typeof left === 'string' && typeof right !== 'string') {
    return repeatString(left, right)
  }

  if (typeof right === 'string' && typeof left !== 'string') {
    return repeatString(right, left)
  }

  if (typeof left !== 'number' || typeof right !== 'number') {
    throw new TypeError('prod(): values must be numbers or repeatable strings')
  }

  const leftNumber = left
  const rightNumber = right

  if (Number.isInteger(leftNumber) && Number.isInteger(rightNumber)) {
    if (leftNumber === 0 || rightNumber === 0) {
      return 0
    }
    if (leftNumber === 1) {
      return rightNumber
    }
    if (rightNumber === 1) {
      return leftNumber
    }
    if (leftNumber === -1) {
      return -rightNumber
    }
    if (rightNumber === -1) {
      return -leftNumber
    }

    if (!Number.isSafeInteger(leftNumber) || !Number.isSafeInteger(rightNumber)) {
      throw new RangeError('prod(): integer multiplication only supports JS safe integers')
    }

    const result = leftNumber * rightNumber
    if (!Number.isSafeInteger(result)) {
      throw new RangeError('prod(): integer multiplication only supports JS safe integers')
    }

    return result
  }

  return leftNumber * rightNumber
}

function repeatString(value: string, multiplier: ProdValue): string {
  if (typeof multiplier !== 'number') {
    throw new TypeError('prod(): string repetition requires a safe integer multiplier')
  }

  const count = multiplier
  if (!Number.isInteger(count) || !Number.isSafeInteger(count)) {
    throw new TypeError('prod(): string repetition requires a safe integer multiplier')
  }

  return count > 0 ? value.repeat(count) : ''
}