type DataViewGetter = (byteOffset: number, littleEndian?: boolean) => number;
type DataViewSetter = (
  byteOffset: number,
  value: number,
  littleEndian?: boolean,
) => void;

interface DataType {
  [key: string]: {
    u: DataViewGetter;
    p: DataViewSetter;
    bytes: number;
  };
}
const lut: DataType = {
  b: { u: DataView.prototype.getInt8, p: DataView.prototype.setInt8, bytes: 1 },
  B: {
    u: DataView.prototype.getUint8,
    p: DataView.prototype.setUint8,
    bytes: 1,
  },
  h: {
    u: DataView.prototype.getInt16,
    p: DataView.prototype.setInt16,
    bytes: 2,
  },
  H: {
    u: DataView.prototype.getUint16,
    p: DataView.prototype.setUint16,
    bytes: 2,
  },
  i: {
    u: DataView.prototype.getInt32,
    p: DataView.prototype.setInt32,
    bytes: 4,
  },
  I: {
    u: DataView.prototype.getUint32,
    p: DataView.prototype.setUint32,
    bytes: 4,
  },
};

export const pack = (format: string, ...data: number[]) => {
  let pointer = 0;
  if (format.replace(/[<>]/, "").length != data.length) {
    throw "Pack format to Argument count mismatch";
  }
  const bytes: number[] = [];
  let littleEndian = true;
  for (let i = 0; i < format.length; i++) {
    if (format[i] == "<") {
      littleEndian = true;
    } else if (format[i] == ">") {
      littleEndian = false;
    } else {
      pushBytes(format[i], data[pointer]);
      pointer++;
    }
  }

  function pushBytes(formatChar: string, value: number) {
    if (!(formatChar in lut)) {
      throw "Unhandled character '" + formatChar + "' in pack format";
    }
    const dataSize = lut[formatChar].bytes;
    const view = new DataView(new ArrayBuffer(dataSize));
    const dataViewFn = lut[formatChar].p.bind(view);
    dataViewFn(0, value, littleEndian);
    for (let i = 0; i < dataSize; i++) {
      bytes.push(view.getUint8(i));
    }
  }

  return bytes;
};

export const unpack = (format: string, bytes: number[]) => {
  let pointer = 0;
  const data: number[] = [];
  let littleEndian = true;

  for (const c of format) {
    if (c == "<") {
      littleEndian = true;
    } else if (c == ">") {
      littleEndian = false;
    } else {
      pushData(c);
    }
  }

  function pushData(formatChar: string) {
    if (!(formatChar in lut)) {
      throw "Unhandled character '" + formatChar + "' in unpack format";
    }
    const dataSize = lut[formatChar].bytes;
    const view = new DataView(new ArrayBuffer(dataSize));
    for (let i = 0; i < dataSize; i++) {
      view.setUint8(i, bytes[pointer + i] & 0xff);
    }
    const dataViewFn = lut[formatChar].u.bind(view);
    data.push(dataViewFn(0, littleEndian));
    pointer += dataSize;
  }

  return data;
};