@loaders.gl/wkt/src/lib/utils/base64-encoder.ts

Loader and Writer for the WKT (Well Known Text) Format

// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors

/* 
const binary_to_b64_map = [
  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
  'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
  'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a',
  'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
  'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
  't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1',
  '2', '3', '4', '5', '6', '7', '8', '9', '+',
  '/', '='
];
const b64_to_binary_map = {
  '0': 52, '1': 53, '2': 54, '3': 55, '4': 56, '5': 57, '6': 58, '7': 59, '8': 60, '9': 61,
  A: 0, B: 1, C: 2, D: 3, E: 4, F: 5, G: 6, H: 7, I: 8, J: 9, K: 10, L: 11, M: 12, N: 13, O: 14,
  P: 15, Q: 16, R: 17, S: 18, T: 19, U: 20, V: 21, W: 22, X: 23, Y: 24, Z: 25, a: 26, b: 27,
  c: 28, d: 29, e: 30, f: 31, g: 32, h: 33, i: 34, j: 35, k: 36, l: 37, m: 38, n: 39, o: 40,
  p: 41, q: 42, r: 43, s: 44, t: 45, u: 46, v: 47, w: 48, x: 49, y: 50, z: 51, '+': 62, '/': 63,
  '=': 64
};

*/

export class Base64Encoder {
  getDecodedLength(array: Uint8Array): number {
    return Math.ceil(array.byteLength / 4) * 3;
  }

  decode(array: Uint8Array, target?: ArrayBuffer) {} // eslint-disable-line
}

/*

//generates an array iterator that returns 3 elements at a time. Use to loop through the Uint8Array Array Buffer
// to be converted to Base64.  (binary array buffer) 8bits * 3 = 6bits * 4 (base64 representation)
const generateTripleIterator = (arr) => {
  return {
      *[Symbol.iterator]() {
          for(let n = 0; n < arr.length; n+=3) {
              let result = [];
              result.push(arr[n]);

              if(n+1 < arr.length)
                  result.push(arr[n+1]);
              if(n+2 < arr.length)
                  result.push(arr[n+2]);

              yield result;
          }
      }
  };
};

//generates an array iterator that returns 4 elements at a time.  Use to loop through
// Base64 string because Base64 string is multiples of 4 characters.
const generateQuadrupleIterator = (arr) => {
  return {
      *[Symbol.iterator]() {
          for(let n = 0; n < arr.length; n+=4) {
              yield [...arr.slice(n, n+4)];
          }
      }
  };
};

// Converts a triple of 8 bits into a quadruple of 6 bits.  use to convert binary to base64 representation
const tripleConvert = (first, second, third) => {
  let [] = triple;
  let binary = null, a = null, b = null, c = null, d = null;
  if (triple.length === 1) {
      binary = (first << 4);
      a = ((binary & 4032) >>> 6);
      b = (binary & 63);
      c = 64;
      d = 64;
  } else if (triple.length === 2) {
      binary = ((first << 10) | (second << 2));
      a = ((binary & 258048) >>> 12);
      b = ((binary & 4032) >>> 6);
      c = (binary & 63);
      d = 64;
  } else {
      binary = ((first << 16) | (second << 8) | third);
      a = ((binary & 16515072) >>> 18);
      b = ((binary & 258048) >>> 12);
      c = ((binary & 4032) >>> 6);
      d = (binary & 63);
  }

  return [a, b, c, d];
};

// Converts a quadruple of 6 bits into a triple of 8 bits.  use to convert base64 representation into binary
const quadrupleConvert = (quadruple) => {
  let [a, b, c, d] = quadruple;
  let binary = null, first = null, second = null, third = null;

  if(c === 64 && d === 64) {
      //two padding
      binary = ((a << 6) | b);
      first = (binary >> 4);   //shift off 4 bits, 2 bits per padding
  } else if(d === 64) {
      //one padding
      binary = ((a << 12) | (b << 6) | c );
      binary = (binary >> 2); //shift off 2 bits
      first = binary >> 8;
      second = ((binary << 24) >>> 24);
  } else {
      //no padding
      binary = ((a << 18) | (b << 12) | (c << 6) | d );
      first = (binary >>> 16);
      second = ((binary << 16) >>> 24);
      third = ((binary << 24) >>> 24);
  }

  return [first, second, third];
};

// Convert 8Bits Array Buffer to Base64 string
export const ab2b64 = (buffer) => {
  const b64strArray = [];
  const view = new Uint8Array(buffer);
  let iterator = generateTripleIterator(view);
  for(let triple of iterator) {
      b64strArray.push(...tripleConvert(triple));
  }
  return b64strArray.map(b64CharCodePoint => binary_to_b64_map[b64CharCodePoint]).join("");
};

// Convert Base64 String to 8Bits Array Buffer
export const b642ab = (b64str) => {
  let buffer_length = (b64str.length / 4) * 3;
  if(b64str.slice(-2) === '==') {
      buffer_length -= 2;
  } else if(b64str.slice(-1) === '=') {
      buffer_length -= 1;
  }

  let buffer = new ArrayBuffer(buffer_length);
  const view = new Uint8Array(buffer);
  let iterator = generateQuadrupleIterator(b64str.split("").map(b64char => b64_to_binary_map[b64char]));
  let byteIndex = 0;
  for(let quadruple of iterator) {
      quadrupleConvert(quadruple).forEach(byte => {
          if(byte != null) {
              view[byteIndex] = byte;
              byteIndex++;
          }
      });
  }
  return buffer;
};

*/