const BitArray = require('node-bitarray');
const range = require('range').range;

export const Bit = {
  // returns a boolean array representing the bits of the input (MSB to LSB)
  parse(input: number, bitCount: number): boolean[] {
    const bits = [];
    let tmp = input;

    while (tmp > 0) {
      bits.push(tmp % 2);
      tmp = Math.floor(tmp / 2);
    }

    // prepend empty values to satisfy bitcount
    while (bitCount && bitCount > bits.length) {
      bits.push(0);
    }

    return bits.reverse();
  }
};


export function writeIntToBuffer(buffer: Buffer, value: number, writeLength: number, offset = 0): Buffer {
  const inputBits: number[] = BitArray.parse(value);
  const bufferBits = BitArray.fromBuffer(buffer).toArray();

  if (inputBits.length > writeLength) {
    throw new Error(`Number must fit in provided space. Required space: ${inputBits.length}, available space: ${writeLength}`);
  }

  // pad inputbits with 0's to take up full writeLength
  range(writeLength - inputBits.length).map(() => inputBits.unshift(0));

  // substitute appropriate part of config with input
  const newBufferBits = bufferBits
    .slice(0, offset)
    .concat(inputBits)
    .concat(bufferBits.slice(offset + writeLength));

  return BitArray.factory(newBufferBits).toBuffer();
}