const parseIndex = (input: number | string, length: number): number => {
  if (typeof input === 'number') {
    return Math.trunc(input)
  }

  const token = String(input).trim()
  if (token === 'end') {
    return length - 1
  }

  const endOffset = token.match(/^end-(\d+)$/)
  if (endOffset?.[1]) {
    return length - 1 - Number(endOffset[1])
  }

  return Math.trunc(Number(token))
}

export function range(str: string, first: number | string, last: number | string): string {
  //      discuss at: https://locutus.io/tcl/range/
  // parity verified: Tcl 8.6
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //       example 1: range('Hello World', 0, 4)
  //       returns 1: 'Hello'
  //       example 2: range('Hello World', 6, 'end')
  //       returns 2: 'World'
  //       example 3: range('abcdef', 1, 'end-1')
  //       returns 3: 'bcde'

  const value = String(str)
  const len = value.length
  let start = parseIndex(first, len)
  let end = parseIndex(last, len)

  if (!Number.isFinite(start)) {
    start = 0
  }
  if (!Number.isFinite(end)) {
    end = -1
  }

  start = Math.max(0, start)
  end = Math.min(len - 1, end)

  if (start > end || len === 0) {
    return ''
  }

  return value.slice(start, end + 1)
}