//binary data writer tuned for encoding binary specific to the postgres binary protocol

export class Writer {
  private buffer: Buffer;
  private offset: number = 5;
  private headerPosition: number = 0;
  constructor(private size = 256) {
    this.buffer = Buffer.alloc(size)
  }

  private ensure(size: number): void {
    var remaining = this.buffer.length - this.offset;
    if (remaining < size) {
      var oldBuffer = this.buffer;
      // exponential growth factor of around ~ 1.5
      // https://stackoverflow.com/questions/2269063/buffer-growth-strategy
      var newSize = oldBuffer.length + (oldBuffer.length >> 1) + size;
      this.buffer = Buffer.alloc(newSize);
      oldBuffer.copy(this.buffer);
    }
  }

  public addInt32(num: number): Writer {
    this.ensure(4);
    this.buffer[this.offset++] = (num >>> 24 & 0xFF);
    this.buffer[this.offset++] = (num >>> 16 & 0xFF);
    this.buffer[this.offset++] = (num >>> 8 & 0xFF);
    this.buffer[this.offset++] = (num >>> 0 & 0xFF);
    return this;
  }

  public addInt16(num: number): Writer {
    this.ensure(2);
    this.buffer[this.offset++] = (num >>> 8 & 0xFF);
    this.buffer[this.offset++] = (num >>> 0 & 0xFF);
    return this;
  }


  public addCString(string: string): Writer {
    if (!string) {
      this.ensure(1);
    } else {
      var len = Buffer.byteLength(string);
      this.ensure(len + 1); // +1 for null terminator
      this.buffer.write(string, this.offset, 'utf-8')
      this.offset += len;
    }

    this.buffer[this.offset++] = 0; // null terminator
    return this;
  }

  public addString(string: string = ""): Writer {
    var len = Buffer.byteLength(string);
    this.ensure(len);
    this.buffer.write(string, this.offset);
    this.offset += len;
    return this;
  }

  public add(otherBuffer: Buffer): Writer {
    this.ensure(otherBuffer.length);
    otherBuffer.copy(this.buffer, this.offset);
    this.offset += otherBuffer.length;
    return this;
  }

  private join(code?: number): Buffer {
    if (code) {
      this.buffer[this.headerPosition] = code;
      //length is everything in this packet minus the code
      const length = this.offset - (this.headerPosition + 1)
      this.buffer.writeInt32BE(length, this.headerPosition + 1)
    }
    return this.buffer.slice(code ? 0 : 5, this.offset);
  }

  public flush(code?: number): Buffer {
    var result = this.join(code);
    this.offset = 5;
    this.headerPosition = 0;
    this.buffer = Buffer.allocUnsafe(this.size)
    return result;
  }
}