var parseBits = function(data, bits, offset, invert, callback) {
  offset = offset || 0;
  invert = invert || false;
  callback = callback || function(lastValue, newValue, bits) { return (lastValue * Math.pow(2, bits)) + newValue; };
  var offsetBytes = offset >> 3;

  var inv = function(value) {
    if (invert) {
      return ~value & 0xff;
    }

    return value;
  };

  // read first (maybe partial) byte
  var mask = 0xff;
  var firstBits = 8 - (offset % 8);
  if (bits < firstBits) {
    mask = (0xff << (8 - bits)) & 0xff;
    firstBits = bits;
  }

  if (offset) {
    mask = mask >> (offset % 8);
  }

  var result = 0;
  if ((offset % 8) + bits >= 8) {
    result = callback(0, inv(data[offsetBytes]) & mask, firstBits);
  }

  // read bytes
  var bytes = (bits + offset) >> 3;
  for (var i = offsetBytes + 1; i < bytes; i++) {
    result = callback(result, inv(data[i]), 8);
  }

  // bits to read, that are not a complete byte
  var lastBits = (bits + offset) % 8;
  if (lastBits > 0) {
    result = callback(result, inv(data[bytes]) >> (8 - lastBits), lastBits);
  }

  return result;
};

var parseFloatFromBits = function(data, precisionBits, exponentBits) {
  var bias = Math.pow(2, exponentBits - 1) - 1;
  var sign = parseBits(data, 1);
  var exponent = parseBits(data, exponentBits, 1);

  if (exponent === 0) {
    return 0;
  }

  // parse mantissa
  var precisionBitsCounter = 1;
  var parsePrecisionBits = function(lastValue, newValue, bits) {
    if (lastValue === 0) {
      lastValue = 1;
    }

    for (var i = 1; i <= bits; i++) {
      precisionBitsCounter /= 2;
      if ((newValue & (0x1 << (bits - i))) > 0) {
        lastValue += precisionBitsCounter;
      }
    }

    return lastValue;
  };

  var mantissa = parseBits(data, precisionBits, exponentBits + 1, false, parsePrecisionBits);

  // special cases
  if (exponent == (Math.pow(2, exponentBits + 1) - 1)) {
    if (mantissa === 0) {
      return (sign === 0) ? Infinity : -Infinity;
    }

    return NaN;
  }

  // normale number
  return ((sign === 0) ? 1 : -1) * Math.pow(2, exponent - bias) * mantissa;
};

var parseInt16 = function(value) {
  if (parseBits(value, 1) == 1) {
    return -1 * (parseBits(value, 15, 1, true) + 1);
  }

  return parseBits(value, 15, 1);
};

var parseInt32 = function(value) {
  if (parseBits(value, 1) == 1) {
    return -1 * (parseBits(value, 31, 1, true) + 1);
  }

  return parseBits(value, 31, 1);
};

var parseFloat32 = function(value) {
  return parseFloatFromBits(value, 23, 8);
};

var parseFloat64 = function(value) {
  return parseFloatFromBits(value, 52, 11);
};

var parseNumeric = function(value) {
  var sign = parseBits(value, 16, 32);
  if (sign == 0xc000) {
    return NaN;
  }

  var weight = Math.pow(10000, parseBits(value, 16, 16));
  var result = 0;

  var digits = [];
  var ndigits = parseBits(value, 16);
  for (var i = 0; i < ndigits; i++) {
    result += parseBits(value, 16, 64 + (16 * i)) * weight;
    weight /= 10000;
  }

  var scale = Math.pow(10, parseBits(value, 16, 48));
  return ((sign === 0) ? 1 : -1) * Math.round(result * scale) / scale;
};

var parseDate = function(isUTC, value) {
  var sign = parseBits(value, 1);
  var rawValue = parseBits(value, 63, 1);

  // discard usecs and shift from 2000 to 1970
  var result = new Date((((sign === 0) ? 1 : -1) * rawValue / 1000) + 946684800000);

  if (!isUTC) {
    result.setTime(result.getTime() + result.getTimezoneOffset() * 60000);
  }

  // add microseconds to the date
  result.usec = rawValue % 1000;
  result.getMicroSeconds = function() {
    return this.usec;
  };
  result.setMicroSeconds = function(value) {
    this.usec = value;
  };
  result.getUTCMicroSeconds = function() {
    return this.usec;
  };

  return result;
};

var parseArray = function(value) {
  var dim = parseBits(value, 32);

  var flags = parseBits(value, 32, 32);
  var elementType = parseBits(value, 32, 64);

  var offset = 96;
  var dims = [];
  for (var i = 0; i < dim; i++) {
    // parse dimension
    dims[i] = parseBits(value, 32, offset);
    offset += 32;

    // ignore lower bounds
    offset += 32;
  }

  var parseElement = function(elementType) {
    // parse content length
    var length = parseBits(value, 32, offset);
    offset += 32;

    // parse null values
    if (length == 0xffffffff) {
      return null;
    }

    var result;
    if ((elementType == 0x17) || (elementType == 0x14)) {
      // int/bigint
      result = parseBits(value, length * 8, offset);
      offset += length * 8;
      return result;
    }
    else if (elementType == 0x19) {
      // string
      result = value.toString(this.encoding, offset >> 3, (offset += (length << 3)) >> 3);
      return result;
    }
    else {
      console.log("ERROR: ElementType not implemented: " + elementType);
    }
  };

  var parse = function(dimension, elementType) {
    var array = [];
    var i;

    if (dimension.length > 1) {
      var count = dimension.shift();
      for (i = 0; i < count; i++) {
        array[i] = parse(dimension, elementType);
      }
      dimension.unshift(count);
    }
    else {
      for (i = 0; i < dimension[0]; i++) {
        array[i] = parseElement(elementType);
      }
    }

    return array;
  };

  return parse(dims, elementType);
};

var parseText = function(value) {
  return value.toString('utf8');
};

var parseBool = function(value) {
  if(value === null) return null;
  return (parseBits(value, 8) > 0);
};

var init = function(register) {
  register(21, parseInt16);
  register(23, parseInt32);
  register(26, parseInt32);
  register(1700, parseNumeric);
  register(700, parseFloat32);
  register(701, parseFloat64);
  register(16, parseBool);
  register(1114, parseDate.bind(null, false));
  register(1184, parseDate.bind(null, true));
  register(1000, parseArray);
  register(1007, parseArray);
  register(1016, parseArray);
  register(1008, parseArray);
  register(1009, parseArray);
  register(25, parseText);
};

module.exports = {
  init: init
};
