private _readOrSeekToChunk()

in packages/selector/src/text/seeker.ts [259:310]
41 lines of code
11 McCabe index (conditional complexity)

  private _readOrSeekToChunk(
    read: false,
    target: TChunk,
    offset?: number,
  ): void;
  private _readOrSeekToChunk(
    read: boolean,
    target: TChunk,
    offset = 0,
  ): string | void {
    const oldPosition = this.position;
    let result = '';

    // Walk to the requested chunk.
    if (!this.chunker.precedesCurrentChunk(target)) {
      // Search forwards.
      while (!chunkEquals(this.currentChunk, target)) {
        const [data, nextChunk] = this._readToNextChunk();
        if (read) result += data;
        if (nextChunk === null) throw new RangeError(E_END);
      }
    } else {
      // Search backwards.
      while (!chunkEquals(this.currentChunk, target)) {
        const [data, previousChunk] = this._readToPreviousChunk();
        if (read) result = data + result;
        if (previousChunk === null) throw new RangeError(E_END);
      }
    }

    // Now we know where the chunk is, walk to the requested offset.
    // Note we might have started inside the chunk, and the offset could even
    // point at a position before or after the chunk.
    const targetPosition = this.currentChunkPosition + offset;
    if (!read) {
      this.seekTo(targetPosition);
    } else {
      if (targetPosition >= this.position) {
        // Read further until the target.
        result += this.readTo(targetPosition);
      } else if (targetPosition >= oldPosition) {
        // We passed by our target position: step back.
        this.seekTo(targetPosition);
        result = result.slice(0, targetPosition - oldPosition);
      } else {
        // The target precedes our starting position: read backwards from there.
        this.seekTo(oldPosition);
        result = this.readTo(targetPosition);
      }
      return result;
    }
  }