import getRandomValues from 'get-random-values-esm'

// WHATWG crypto RNG - https://w3c.github.io/webcrypto/Overview.html
function whatwgRNG(length = 16) {
  const rnds8 = new Uint8Array(length)
  getRandomValues(rnds8)
  return rnds8
}

const getByteHexTable = (() => {
  let table: string[]
  return () => {
    if (table) {
      return table
    }
    table = []
    for (let i = 0; i < 256; ++i) {
      table[i] = (i + 0x100).toString(16).substring(1)
    }
    return table
  }
})()

export function randomKey(length?: number) {
  const table = getByteHexTable()
  return whatwgRNG(length)
    .reduce((str, n) => str + table[n], '')
    .slice(0, length)
}