function EncodeVarNumber(
  dst: Uint8Array,
  offset: number,
  value: number,
): number {
  value = (value | 0) >>> 0; // 32-bit integer

  while (value > 127) {
    dst[offset++] = (value & 0b01111111) | 0b10000000;
    value >>>= 7;
  }
  dst[offset++] = value;

  return offset;
}

function DecodeVarNumber(
  buf: Uint8Array,
  offset: number,
): [value: number, offset: number] {
  let value = 0;
  let shift = 0;

  while (true) {
    const byte = buf[offset++]!;
    value |= (byte & 0b01111111) << shift;
    if (byte < 128) {
      break;
    }
    shift += 7;
  }

  return [value | 0, offset];
}

function DecodeVarBigInt(
  buf: Uint8Array,
  offset: number,
): [value: bigint, offset: number] {
  let value = BigInt(0);
  let shift = BigInt(0);

  while (true) {
    const byte = buf[offset++]!;
    value |= BigInt(byte & 0b01111111) << shift;
    if (byte < 128) {
      break;
    }
    shift += BigInt(7);
  }

  return [BigInt.asIntN(64, value), offset];
}

export function $varint_decode_i32(
  buf: Uint8Array,
  offset: number,
): [value: number, offset: number] {
  const [v, o] = DecodeVarNumber(buf, offset);
  return [v, o];
}

export function $varint_decode_u32(
  buf: Uint8Array,
  offset: number,
): [value: number, offset: number] {
  const [v, o] = DecodeVarNumber(buf, offset);
  return [v >>> 0, o];
}

export function $varint_decode_i64(
  buf: Uint8Array,
  offset: number,
): [value: bigint, offset: number] {
  const [v, o] = DecodeVarBigInt(buf, offset);
  return [v, o];
}

export function $varint_decode_u64(
  buf: Uint8Array,
  offset: number,
): [value: bigint, offset: number] {
  const [v, o] = DecodeVarBigInt(buf, offset);
  return [BigInt.asUintN(64, v), o];
}

function EncodeVarBigInt(
  dst: Uint8Array,
  offset: number,
  value: bigint,
): number {
  value = BigInt.asUintN(64, value);

  while (value > BigInt(127)) {
    dst[offset++] = Number(value & BigInt(0b01111111)) | 0b10000000;
    value >>= BigInt(7);
  }
  dst[offset++] = Number(value);

  return offset;
}

export function $varint_encode(
  dst: Uint8Array,
  offset: number,
  value: number,
): number;
export function $varint_encode(
  dst: Uint8Array,
  offset: number,
  value: bigint,
): number;

export function $varint_encode(
  dst: Uint8Array,
  offset: number,
  value: number | bigint,
): number {
  if (typeof value === "bigint") {
    offset = EncodeVarBigInt(dst, offset, value);
  } else {
    if (value < 0) {
      // NOTE: Protocol Buffers signed varint encoding uses two's complement of 64-bit unsigned integers.
      offset = EncodeVarBigInt(dst, offset, BigInt(value));
    } else {
      offset = EncodeVarNumber(dst, offset, value);
    }
  }
  return offset;
}