const binary2hex = {
  '0000': 0,
  '0001': 1,
  '0010': 2,
  '0011': 3,
  '0100': 4,
  '0101': 5,
  '0110': 6,
  '0111': 7,
  1000: 8,
  1001: 9,
  1010: 'A',
  1011: 'B',
  1100: 'C',
  1101: 'D',
  1110: 'E',
  1111: 'F',
} as const;

export function binaryArray2bytes (array: ReadonlyArray<0 | 1>): Buffer {
  const bufArray: Buffer[] = [];

  for (let i = 0; i < array.length; i += 8) {
    if (i + 7 > array.length) break;

    const binString1 = `${array[i]}${array[i + 1]}${array[i + 2]}${
      array[i + 3]
    }` as const;
    const binString2 = `${array[i + 4]}${array[i + 5]}${array[i + 6]}${
      array[i + 7]
    }` as const;

    const hexChar1 = binary2hex[binString1];
    const hexChar2 = binary2hex[binString2];

    const buf = Buffer.from(`${hexChar1}${hexChar2}`, 'hex');
    bufArray.push(buf);
  }

  return Buffer.concat(bufArray);
}

const hex2binary = {
  0: [0, 0, 0, 0],
  1: [0, 0, 0, 1],
  2: [0, 0, 1, 0],
  3: [0, 0, 1, 1],
  4: [0, 1, 0, 0],
  5: [0, 1, 0, 1],
  6: [0, 1, 1, 0],
  7: [0, 1, 1, 1],
  8: [1, 0, 0, 0],
  9: [1, 0, 0, 1],
  A: [1, 0, 1, 0],
  B: [1, 0, 1, 1],
  C: [1, 1, 0, 0],
  D: [1, 1, 0, 1],
  E: [1, 1, 1, 0],
  F: [1, 1, 1, 1],
} as const;

export function bytes2binaryArray (buf: Buffer): Array<0 | 1> {
  const hexString = buf.toString('hex').toUpperCase();
  const array: Array<0 | 1> = [];
  for (let i = 0; i < hexString.length; i++) {
    const hexChar = hexString.charAt(i) as keyof typeof hex2binary;
    array.push(...hex2binary[hexChar]);
  }
  return array;
}

export function insertZerosEvery7Bits (buf: Buffer): Buffer {
  const binaryArray = bytes2binaryArray(buf);
  const newBinaryArray: Array<0 | 1> = [];
  for (let i = 0; i < binaryArray.length; i++) {
    newBinaryArray.push(binaryArray[i]);

    if ((i + 1) % 7 === 0) {
      newBinaryArray.push(0);
    }
  }
  return binaryArray2bytes(newBinaryArray);
}