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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
/** Type for a ULID generator function. */export type ULID = (seedTime?: number) => string;
// These values should NEVER change. If// they do, we're no longer making ulids!export const ENCODING = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"; // Crockford's Base32export const ENCODING_LEN = ENCODING.length;export const TIME_MAX = Math.pow(2, 48) - 1;export const TIME_LEN = 10;export const RANDOM_LEN = 16;
function replaceCharAt(str: string, index: number, char: string) {  return str.substring(0, index) + char + str.substring(index + 1);}
export function encodeTime(now: number, len: number = TIME_LEN): string {  if (!Number.isInteger(now) || now < 0 || now > TIME_MAX) {    throw new Error("Time must be a positive integer less than " + TIME_MAX);  }  let str = "";  for (; len > 0; len--) {    const mod = now % ENCODING_LEN;    str = ENCODING[mod] + str;    now = (now - mod) / ENCODING_LEN;  }  return str;}
export function encodeRandom(len: number): string {  let str = "";  const randomBytes = crypto.getRandomValues(new Uint8Array(len));  for (const randomByte of randomBytes) {    str += ENCODING[randomByte % ENCODING_LEN];  }  return str;}
export function incrementBase32(str: string): string {  let index = str.length;  let char;  let charIndex;  const maxCharIndex = ENCODING_LEN - 1;  while (--index >= 0) {    char = str[index]!;    charIndex = ENCODING.indexOf(char);    if (charIndex === -1) {      throw new Error("incorrectly encoded string");    }    if (charIndex === maxCharIndex) {      str = replaceCharAt(str, index, ENCODING[0]!);      continue;    }    return replaceCharAt(str, index, ENCODING[charIndex + 1]!);  }  throw new Error("cannot increment this string");}
/** Generates a monotonically increasing ULID. */export function monotonicFactory(encodeRand = encodeRandom): ULID {  let lastTime = 0;  let lastRandom: string;  return function ulid(seedTime: number = Date.now()): string {    if (seedTime <= lastTime) {      const incrementedRandom = (lastRandom = incrementBase32(lastRandom));      return encodeTime(lastTime, TIME_LEN) + incrementedRandom;    }    lastTime = seedTime;    const newRandom = (lastRandom = encodeRand(RANDOM_LEN));    return encodeTime(seedTime, TIME_LEN) + newRandom;  };}