const TypeTxt = 16;
const TypePtr = 12;
const TypeSrv = 33;
const TypeA = 1;

export class Question {
  public name = "";
  public type = 0;
  public class = 0;
  public endOffset = 0;
}

export abstract class Record {
  public type = 0;
  public ttlSeconds = 0;
  public name = "";
  public endOffset = -1;
}

export class PtrRecord extends Record {
  public domain = "";
}

export class TxtRecord extends Record {
  public text = "";
}

export class SrvRecord extends Record {
  public priority = 0;
  public weight = 0;
  public port = 0;
  public target = "";
}

export class ARecord extends Record {
  public address = 0;

  public get addressStr(): string {
    return ipToString(this.address);
  }
}

export function ipToString(ip: number): string {
  const o1 = (ip >> 24) & 0xff;
  const o2 = (ip >> 16) & 0xff;
  const o3 = (ip >> 8) & 0xff;
  const o4 = (ip >> 0) & 0xff;
  const addressStr = `${o1.toString()}.${o2.toString()}.${o3.toString()}.${o4.toString()}`;
  return addressStr;
}

class dnsAnswerParseResult {
  public name = "";
  public endOffset = 0;
}

function parseDnsName(msg: Buffer, startOffset: number): dnsAnswerParseResult {
  const result = new dnsAnswerParseResult();
  let offset = startOffset;

  while (offset < msg.length) {
    const nextByte = msg.readUInt8(offset);
    if (nextByte === 0) {
      offset++;
      break;
    }

    const pointerMask = (1 << 6) | (1 << 7);
    if ((nextByte & pointerMask) === pointerMask) {
      offset++;
      const pointerOffset = msg.readUInt8(offset);
      offset++;
      const nestedResult = parseDnsName(msg, pointerOffset);
      if (result.name.length > 0 && nestedResult.name.length > 0) {
        result.name += ".";
      }
      result.name += nestedResult.name;
      break;
    }

    offset++;
    const segment = msg.toString("ascii", offset, offset + nextByte);
    offset += nextByte;
    if (result.name.length > 0 && segment.length > 0) {
      result.name += ".";
    }
    result.name += segment;
  }

  result.endOffset = offset;
  return result;
}

export function GetDNSQuestion(msg: Buffer, startOffset: number): Question {
  let offset = startOffset;
  const parsedResult = parseDnsName(msg, offset);
  offset = parsedResult.endOffset;
  const type = msg.readUInt16BE(offset);
  offset += 2;
  const cls = msg.readUInt16BE(offset);
  offset += 2;

  const ret = new Question();
  ret.name = parsedResult.name;
  ret.type = type;
  ret.class = cls;
  ret.endOffset = offset;
  return ret;
}

export function GetDNSAnswer(
  msg: Buffer,
  startOffset: number,
): Record | undefined {
  let offset = startOffset;
  const parsedResult = parseDnsName(msg, offset);
  offset = parsedResult.endOffset;

  const type = msg.readUInt16BE(offset);
  offset += 2;
  offset += 2; // don't care about "class" of answer
  const ttlSeconds = msg.readUInt32BE(offset);
  offset += 4;
  const rDataLength = msg.readUInt16BE(offset);
  offset += 2;

  switch (type) {
    case TypePtr: {
      const domainResult = parseDnsName(msg, offset);

      const ret = new PtrRecord();
      ret.type = type;
      ret.ttlSeconds = ttlSeconds;
      ret.name = parsedResult.name;
      ret.endOffset = offset + rDataLength;
      ret.domain = domainResult.name;
      return ret;
    }

    case TypeTxt: {
      const textResult = parseDnsName(msg, offset);

      const ret = new TxtRecord();
      ret.type = type;
      ret.ttlSeconds = ttlSeconds;
      ret.name = parsedResult.name;
      ret.endOffset = offset + rDataLength;
      ret.text = textResult.name;
      return ret;
    }

    case TypeSrv: {
      const priority = msg.readUInt16BE(offset);
      const weight = msg.readUInt16BE(offset + 2);
      const port = msg.readUInt16BE(offset + 4);
      const targetResult = parseDnsName(msg, offset + 6);

      const ret = new SrvRecord();
      ret.type = type;
      ret.ttlSeconds = ttlSeconds;
      ret.name = parsedResult.name;
      ret.endOffset = offset + rDataLength;
      ret.priority = priority;
      ret.weight = weight;
      ret.port = port;
      ret.target = targetResult.name;
      return ret;
    }

    case TypeA: {
      const address = msg.readUInt32BE(offset);

      const ret = new ARecord();
      ret.type = type;
      ret.ttlSeconds = ttlSeconds;
      ret.name = parsedResult.name;
      ret.endOffset = offset + rDataLength;
      ret.address = address;
      return ret;
    }

    default:
      break;
  }

  return undefined;
}