// Copyright 2018-2025 the Deno authors. MIT license.
/** Type for a ULID generator function. */
// deno-lint-ignore deno-style-guide/naming-convention
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 Base32
export const ENCODING_LEN = ENCODING.length;
export const TIME_MAX = Math.pow(2, 48) - 1;
export const TIME_LEN = 10;
export const RANDOM_LEN = 16;
export const ULID_LEN = TIME_LEN + RANDOM_LEN;
function replaceCharAt(str: string, index: number, char: string) {
return str.substring(0, index) + char + str.substring(index + 1);
}
export function encodeTime(timestamp: number): string {
if (!Number.isInteger(timestamp) || timestamp < 0 || timestamp > TIME_MAX) {
throw new RangeError(
`Time must be a positive integer less than ${TIME_MAX}`,
);
}
let str = "";
for (let len = TIME_LEN; len > 0; len--) {
const mod = timestamp % ENCODING_LEN;
str = ENCODING[mod] + str;
timestamp = Math.floor(timestamp / ENCODING_LEN);
}
return str;
}
export function encodeRandom(): string {
let str = "";
const bytes = crypto.getRandomValues(new Uint8Array(RANDOM_LEN));
for (const byte of bytes) {
str += ENCODING[byte % 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 TypeError("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) + incrementedRandom;
}
lastTime = seedTime;
const newRandom = (lastRandom = encodeRand());
return encodeTime(seedTime) + newRandom;
};
}
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