openchemlib/lib/canvas_editor/utils.js

Manipulate molecules

'use strict';

/* eslint-disable unicorn/prefer-code-point */

// https://github.com/niklasvh/base64-arraybuffer/blob/master/LICENSE
const chars =
  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
// Use a lookup table to find the index.
const lookup = new Uint8Array(256);
for (let i = 0; i < chars.length; i++) {
  lookup[chars.charCodeAt(i)] = i;
}

function decodeBase64(base64) {
  let bufferLength = base64.length * 0.75;
  let len = base64.length;
  let i;
  let p = 0;
  let encoded1;
  let encoded2;
  let encoded3;
  let encoded4;

  if (base64.at(-1) === '=') {
    bufferLength--;
    if (base64.at(-2) === '=') {
      bufferLength--;
    }
  }

  const arraybuffer = new ArrayBuffer(bufferLength);
  const bytes = new Uint8Array(arraybuffer);

  for (i = 0; i < len; i += 4) {
    encoded1 = lookup[base64.charCodeAt(i)];
    encoded2 = lookup[base64.charCodeAt(i + 1)];
    encoded3 = lookup[base64.charCodeAt(i + 2)];
    encoded4 = lookup[base64.charCodeAt(i + 3)];

    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
  }

  return arraybuffer;
}

function toHex(v) {
  return v.toString(16).padStart(2, '0');
}

module.exports = {
  decodeBase64,
  toHex,
};