// GPG4Browsers - An OpenPGP implementation in javascript
// Copyright (C) 2011 Recurity Labs GmbH
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 3.0 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

// The GPG4Browsers crypto interface

/**
 * @fileoverview Provides tools for retrieving secure randomness from browsers or Node.js
 * @requires util
 * @module crypto/random
 */
import util from '../util';

const nodeCrypto = util.getNodeCrypto();

/**
 * Buffer for secure random numbers
 */
class RandomBuffer {
  constructor() {
    this.buffer = null;
    this.size = null;
    this.callback = null;
  }

  /**
   * Initialize buffer
   * @param  {Integer} size size of buffer
   */
  init(size, callback) {
    this.buffer = new Uint8Array(size);
    this.size = 0;
    this.callback = callback;
  }

  /**
   * Concat array of secure random numbers to buffer
   * @param {Uint8Array} buf
   */
  set(buf) {
    if (!this.buffer) {
      throw new Error('RandomBuffer is not initialized');
    }
    if (!(buf instanceof Uint8Array)) {
      throw new Error('Invalid type: buf not an Uint8Array');
    }
    const freeSpace = this.buffer.length - this.size;
    if (buf.length > freeSpace) {
      buf = buf.subarray(0, freeSpace);
    }
    // set buf with offset old size of buffer
    this.buffer.set(buf, this.size);
    this.size += buf.length;
  }

  /**
   * Take numbers out of buffer and copy to array
   * @param {Uint8Array} buf the destination array
   */
  async get(buf) {
    if (!this.buffer) {
      throw new Error('RandomBuffer is not initialized');
    }
    if (!(buf instanceof Uint8Array)) {
      throw new Error('Invalid type: buf not an Uint8Array');
    }
    if (this.size < buf.length) {
      if (!this.callback) {
        throw new Error('Random number buffer depleted');
      }
      // Wait for random bytes from main context, then try again
      await this.callback();
      return this.get(buf);
    }
    for (let i = 0; i < buf.length; i++) {
      buf[i] = this.buffer[--this.size];
      // clear buffer value
      this.buffer[this.size] = 0;
    }
  }
}

/**
 * Retrieve secure random byte array of the specified length
 * @param {Integer} length Length in bytes to generate
 * @returns {Uint8Array} Random byte array
 * @async
 */
export async function getRandomBytes(length) {
  const buf = new Uint8Array(length);
  if (typeof crypto !== 'undefined' && crypto.getRandomValues) {
    crypto.getRandomValues(buf);
  } else if (typeof globalThis !== 'undefined' && typeof globalThis.msCrypto === 'object' && typeof globalThis.msCrypto.getRandomValues === 'function') {
    globalThis.msCrypto.getRandomValues(buf);
  } else if (nodeCrypto) {
    const bytes = nodeCrypto.randomBytes(buf.length);
    buf.set(bytes);
  } else if (randomBuffer.buffer) {
    await randomBuffer.get(buf);
  } else {
    throw new Error('No secure random number generator available.');
  }
  return buf;
}

/**
 * Create a secure random BigInteger that is greater than or equal to min and less than max.
 * @param {module:BigInteger} min Lower bound, included
 * @param {module:BigInteger} max Upper bound, excluded
 * @returns {module:BigInteger} Random BigInteger
 * @async
 */
export async function getRandomBigInteger(min, max) {
  const BigInteger = await util.getBigInteger();

  if (max.lt(min)) {
    throw new Error('Illegal parameter value: max <= min');
  }

  const modulus = max.sub(min);
  const bytes = modulus.byteLength();

  // Using a while loop is necessary to avoid bias introduced by the mod operation.
  // However, we request 64 extra random bits so that the bias is negligible.
  // Section B.1.1 here: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf
  const r = new BigInteger(await getRandomBytes(bytes + 8));
  return r.mod(modulus).add(min);
}

export const randomBuffer = new RandomBuffer();