import { BufferReader } from '@node-dlc/bufio';

/**
 * Reads TLVs from a reader until the entire stream is processed. The handler is
 * responsible for doing something with the data bytes.
 * @param reader
 * @param handler
 */
export function readTlvs(
  reader: BufferReader,
  handler: (type: bigint, value: BufferReader) => boolean,
) {
  let lastType: bigint;
  while (!reader.eof) {
    const type = reader.readBigSize();
    const len = reader.readBigSize();
    const value = reader.readBytes(Number(len));
    const valueReader = new BufferReader(value);

    if (type <= lastType) {
      throw new Error('Invalid TLV stream');
    }

    const isEven = type % BigInt(2) === BigInt(0);
    const wasHandled = handler(type, valueReader);

    if (!wasHandled && isEven) {
      throw new Error('Unknown even type');
    }

    if (wasHandled && !valueReader.eof) {
      throw new Error('Non-canonical length');
    }

    lastType = type;
  }
}