import BitArray from './BitArray.js';

export default class MultiBitArray {
  private readonly bitArray: BitArray;
  private readonly bitsPerEntry: number;

  private constructor(buffer: Buffer, bitsPerEntry: number) {
    this.bitArray = new BitArray(buffer);
    this.bitsPerEntry = bitsPerEntry;
  }

  static fromBuffer(buffer: Buffer, bitsPerEntry: number): MultiBitArray {
    if (!Number.isInteger(bitsPerEntry) || bitsPerEntry < 1) {
      throw new Error('Bits must be an integer >= 1');
    }

    if ((bitsPerEntry & (bitsPerEntry - 1)) !== 0) {
      throw new Error('Bits must be a power of 2');
    }

    return new MultiBitArray(buffer, bitsPerEntry);
  }

  private getBitOffset(index: number): number {
    return index * this.bitsPerEntry;
  }

  get(index: number): number {
    const offset = this.getBitOffset(index);

    let value = 0;

    for (let i = 0; i < this.bitsPerEntry; i++) {
      const bit = this.bitArray.get(offset + i);
      value |= bit << i;
    }

    return value;
  }

  set(index: number, value: number): void {
    const offset = this.getBitOffset(index);

    for (let i = 0; i < this.bitsPerEntry; i++) {
      const bit = (value >> i) & 1;

      if (bit === 1) {
        this.bitArray.set(offset + i);
      } else {
        this.bitArray.unset(offset + i);
      }
    }
  }

  unset(index: number): void {
    const offset = this.getBitOffset(index);

    for (let i = 0; i < this.bitsPerEntry; i++) {
      this.bitArray.unset(offset + i);
    }
  }

  toArray(): Uint8Array {
    return this.bitArray.toArray();
  }
}