'use strict';

var pdns = module.exports;

// Order http://www.zytrax.com/books/dns/ch15/

pdns.unpackHeader = function (i) {
  // i is one element from a Uint16Array (as a 16-bit unsigned integer)

  var header = {
    id:     0                   // added here to preserve console.log order

  , qr:     (i & 0x8000) >> 15  // Query Response (0 is question, 1 is response)
  , opcode: (i & 0x7800) >> 11  // 0 is question
  , aa:     (i &  0x400) >> 10  // Authoritative Answer (response-only)
  , tc:     (i &  0x200) >>  9  // TrunCated - expect another packet with same (?) id
  , rd:     (i &  0x100) >>  8  // Recursion Desired

  , ra:     (i &   0x80) >>  7
  , res1:   (i &   0x40) >>  6  // z
  , res2:   (i &   0x20) >>  5  // ad
  , res3:   (i &   0x10) >>  4  // cd
  , rcode:  (i &    0xF)        // Error Code (response-only)
  };

  return header;
};

pdns.packHeader = function(h) {
  var val = 0;

  val += (h.qr     << 15) & 0x8000;
  val += (h.opcode << 11) & 0x7800;
  val += (h.aa     << 10) &  0x400;
  val += (h.tc     <<  9) &  0x200;
  val += (h.rd     <<  8) &  0x100;
  val += (h.ra     <<  7) &   0x80;
  val += (h.res1   <<  6) &   0x40;
  val += (h.res2   <<  5) &   0x20;
  val += (h.res3   <<  4) &   0x10;
  val += h.rcode          &    0xF;

  return val;
};

pdns.unpackQname = function (ui8) {
  var total = 0;
  var i;

  var len;
  var q = {
    name: ''
  , type: 0
  , class: 0
  };
  var str = [];

  do {
    len = ui8[total];
    if (0xc0 === len) {
      throw new Error("discovered a compression pointer at byte " + total
        + " pointing to byte " + ui8[total + 1]
        + ", but compression pointer support is not yet implemented"
      );
    }
    //str.length = 0; // fast empty array
    if (ui8.byteLength - total < len) {
      throw new Error(
        "Expected a string of length " + len
          + " but packet itself has " + (ui8.byteLength - total) + " bytes remaining"
      );
    }
    for (i = 0; i < len; i += 1) {
      total += 1;
      // TODO check url-allowable characters
      str.push(String.fromCharCode(ui8[total]));
    }
    total += 1;
    if (ui8[total]) {
      // pushd connecting '.', but not trailing
      str.push('.');
    }
    //console.log('total', total, ui8[total], String.fromCharCode(ui8[total]));
  } while (len);

  //str.pop(); // remove trailing '.'

  q.name = str.join('');

  return q;
};

pdns.unpack = function (ab) {
  if (ab.buffer) {
    ab = ab.buffer;
  }

  // SANITY Check
  if (ab.byteLength < 12) {
    throw new Error(
      "A DNS header has a minimum length of 12 bytes but this packet has only " + ab.byteLength + "bytes."
    );
  }

  // DO: new Uint8Array(arrayBuffer);
  // DO NOT: Uint8Array.from(arrayBuffer); // WILL NOT WORK

  // DO: new DataView(arrayBuffer).getUint16(7);
  // DO NOT: arrayBuffer.slice();
  //
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer
  // https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/slice

  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView
  var dv = new DataView(ab);
  var id = dv.getUint16(0);
  var header = pdns.unpackHeader(dv.getUint16(2));
  var qdcount = dv.getUint16(4);  // query count
  var ancount = dv.getUint16(6);  // answer count
  var nscount = dv.getUint16(8);  // authority count
  var arcount = dv.getUint16(10); // additional count
  var total = 12;
  var i;
  var rec;

  // TODO move to pdns.unpackQuestion to make testable
  function unpackQuestion(ab, dv, total) {
    var ototal = total;
    var data = new Uint8Array(ab).slice(total);
    var q = pdns.unpackQname(data);
    total += q.name.length + 2; // account for leading and trailing string length byte


    if (ab.byteLength - total < 4) {
      // console.error(str.join(''));
      throw new Error(
        "Expected a 2-byte QTYPE and 2-byte QCLASS following " + total + "-byte QNAME"
          + " but packet itself has " + (ab.byteLength - total) + " bytes remaining"
      );
    }

    q.type = dv.getUint16(total);
    total += 2;
    q.class = dv.getUint16(total);
    total += 2;
    q.qtotal = total - ototal;
    return q;
  }

  function unpackAnswer(ab, dv, total) {
    var ototal = total;
    var data = new Uint8Array(ab).slice(total);
    var q = pdns.unpackQname(data);
    total += q.name.length + 2; // account for leading and trailing string length byte


    if (ab.byteLength - total < 10) {
      // console.error(str.join(''));
      throw new Error(
        "Expected a 2-byte QTYPE, 2-byte QCLASS, 4-byte TTL, and 2-byte RDLENGTH following " + total + "-byte QNAME"
          + " but packet itself has " + (ab.byteLength - total) + " bytes remaining"
      );
    }

    q.type = dv.getUint16(total);
    total += 2;
    q.class = dv.getUint16(total);
    total += 2;
    q.ttl = dv.getUint32(total);
    total += 4;
    q.rdlength = dv.getUint16(total);
    total += 2;

    // TODO actually parse RDATA
    console.log(ab.byteLength, ab.byteLength - total, ab.byteLength + -total + q.rdlength);
    q.rdata = new Uint8Array(ab).slice(total, total + q.rdlength);
    console.log('q.rdata', q.rdata.byteLength, 'bytes:');
    q.rdata = Array.prototype.slice.apply(q.rdata);
    console.log(q.rdata);
    console.log('total', total);

    total += q.rdlength;
    console.log('total', total);

    q.qtotal = total - ototal;
    return q;
  }

  header.id = id;

  console.log('qdcount', qdcount);
  header.questions = [];
  for (i = 0; i < qdcount; i += 1) {
    rec = unpackQuestion(ab, dv, total);
    total += rec.qtotal;
    header.questions.push(rec);
  }

  console.log('ancount', ancount);
  header.answers = [];
  for (i = 0; i < ancount; i += 1) {
    rec = unpackAnswer(ab, dv, total);
    total += rec.qtotal;
    header.answers.push(rec);
  }

  console.log('nscount', nscount);
  header.authority = [];
  for (i = 0; i < nscount; i += 1) {
    rec = unpackAnswer(ab, dv, total);
    total += rec.qtotal;
    header.authority.push(rec);
  }

  console.log('arcount', arcount);
  header.additional = [];
  for (i = 0; i < arcount; i += 1) {
    rec = unpackAnswer(ab, dv, total);
    total += rec.qtotal;
    header.additional.push(rec);
  }

  if (ab.byteLength !== total) {
    throw new Error(
      "Parsed " + total + " bytes, but packet is " + ab.byteLength + " bytes."
    );
  }
  header.total = total;
  return header;
};