// Loaded from https://raw.githubusercontent.com/nats-io/nats.deno/v1.0.0-rc4/nats-base-client/nuid.ts


/*
* Copyright 2016-2021 The NATS Authors
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

"use strict";

const digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const base = 36;
const preLen = 12;
const seqLen = 10;
const maxSeq = 3656158440062976; // base^seqLen == 36^10
const minInc = 33;
const maxInc = 333;
const totalLen = preLen + seqLen;

const cryptoObj = initCrypto();

function initCrypto() {
  let cryptoObj = null;
  if (typeof globalThis !== "undefined") {
    if ("crypto" in globalThis && globalThis.crypto.getRandomValues) {
      cryptoObj = globalThis.crypto;
    }
  }
  if (!cryptoObj) {
    // shim it
    cryptoObj = {
      getRandomValues: function (array: Uint8Array) {
        for (let i = 0; i < array.length; i++) {
          array[i] = Math.floor(Math.random() * 255);
        }
      },
    };
  }
  return cryptoObj;
}

/**
 * Create and initialize a nuid.
 *
 * @api private
 */
export class Nuid {
  buf: Uint8Array;
  seq!: number;
  inc!: number;

  constructor() {
    this.buf = new Uint8Array(totalLen);
    this.init();
  }

  /**
     * Initializes a nuid with a crypto random prefix,
     * and pseudo-random sequence and increment.
     *
     * @api private
     */
  private init() {
    this.setPre();
    this.initSeqAndInc();
    this.fillSeq();
  }

  /**
     * Initializes the pseudo randmon sequence number and the increment range.
     *
     * @api private
     */
  private initSeqAndInc() {
    this.seq = Math.floor(Math.random() * maxSeq);
    this.inc = Math.floor(Math.random() * (maxInc - minInc) + minInc);
  }

  /**
     * Sets the prefix from crypto random bytes. Converts to base36.
     *
     * @api private
     */
  private setPre() {
    const cbuf = new Uint8Array(preLen);
    cryptoObj.getRandomValues(cbuf);
    for (let i = 0; i < preLen; i++) {
      const di = cbuf[i] % base;
      this.buf[i] = digits.charCodeAt(di);
    }
  }

  /**
     * Fills the sequence part of the nuid as base36 from this.seq.
     *
     * @api private
     */
  private fillSeq() {
    let n = this.seq;
    for (let i = totalLen - 1; i >= preLen; i--) {
      this.buf[i] = digits.charCodeAt(n % base);
      n = Math.floor(n / base);
    }
  }

  /**
     * Returns the next nuid.
     *
     * @api private
     */
  next(): string {
    this.seq += this.inc;
    if (this.seq > maxSeq) {
      this.setPre();
      this.initSeqAndInc();
    }
    this.fillSeq();
    // @ts-ignore - Uint8Arrays can be an argument
    return String.fromCharCode.apply(String, this.buf);
  }

  reset() {
    this.init();
  }
}

export const nuid = new Nuid();