class GridFSFile {
 GridFS fs = null;
 var id;
 String filename;
 String contentType;
 int length;
 int chunkSize;
 DateTime uploadDate;
 Map<String, Object> extraData;
 String md5;

 GridFSFile([Map data = const {}]) {
     this.data = data;
 }

 Future<Map> save() {
   if (fs == null) {
     throw new MongoDartError('Need fs');
   }
   Map tempData = data;
   return fs.files.insert(tempData);
 }

 Future<bool> validate() {
   if (fs == null) {
     throw new MongoDartError('no fs');
   }
   if (md5 == null) {
     throw new MongoDartError('no md5 stored');
   }

   Completer completer = new Completer();
   // query for md5 at filemd5
   DbCommand dbCommand = new DbCommand(
       fs.database,fs.bucketName,0,0,1,{"filemd5" : id}, {"md5" : 1});
   fs.database.executeDbCommand(dbCommand).then((Map data) {
     if (data != null && data.containsKey("md5")) {
       completer.complete(md5 == data["md5"]);
     } else {
       completer.complete(false);
     }
   });
   return completer.future;
 }

 int numChunks() {
   return (length.toDouble() / chunkSize).ceil().toInt();
 }

 List<String> get aliases {
   return extraData["aliases"];
 }

 Map get metaData {
   return extraData["metadata"];
 }

 set metaData(Map metaData) {
   extraData["metadata"] = metaData;
 }

 Map get data {
   Map result = {
     "_id" : id,
     "filename" : filename,
     "contentType" : contentType,
     "length" : length,
     "chunkSize" : chunkSize,
     "uploadDate" : uploadDate,
     "md5" : md5,
   };
   extraData.forEach((String key, Object value) {
     result[key] = value;
   });
   return result;
 }

 set data(Map input) {
   extraData = new Map.from(input);

   // Remove the known keys. Leaving the extraData. 
   id = extraData.remove("_id");
   filename = extraData.remove("filename");
   contentType = extraData.remove("contentType");
   length = extraData.remove("length");
   chunkSize = extraData.remove("chunkSize");
   uploadDate = extraData.remove("uploadDate");
   md5 = extraData.remove("md5");
 }

 void setGridFS( GridFS fs ) {
   this.fs = fs;
 }
}