diff --git a/es/index.js b/es/index.js
new file mode 100644
index 0000000..f8a645b
--- /dev/null
+++ b/es/index.js
@@ -0,0 +1,942 @@
+import _ from 'lodash';
+import read from 'stream-read';
+import mongoose from 'mongoose';
+import { Schema, Mixed, copyInstance, GridFSBucket, MongooseTypes, toCollectionName, model } from '@lykmapipo/mongoose-common';
+export { GridFSBucket } from '@lykmapipo/mongoose-common';
+
+/* constants */
+const WRITABLES = ['_id', 'filename', 'contentType', 'aliases', 'metadata'];
+
+/**
+ * @function createFileSchema
+ * @name createFileSchema
+ * @description Create mongoose schema compactible with gridfs files collection.
+ * @param {object} bucket Valid instance of `GridFSBucket`
+ * @returns {object} valid mongoose schema to access specific gridfs
+ * files collection.
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/#the-files-collection}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @private
+ */
+function createFileSchema(bucket) {
+  // obtain collection name from bucket
+  const collection = bucket.collectionName;
+
+  // gridfs files collection compactible schema
+  // see https://docs.mongodb.com/manual/core/gridfs/#the-files-collection
+  const FileSchema = new Schema(
+    {
+      length: { type: Number, index: true },
+      chunkSize: { type: Number, index: true },
+      uploadDate: { type: Date, index: true },
+      md5: { type: String, trim: true, index: true, searchable: true },
+      filename: { type: String, trim: true, index: true, searchable: true },
+      contentType: { type: String, trim: true, index: true, searchable: true },
+      aliases: { type: [String], sort: true, index: true, searchable: true },
+      metadata: { type: Mixed },
+    },
+    { collection, id: false, emitIndexErrors: true }
+  );
+
+  // expose timestamps as virtuals
+  FileSchema.virtual('createdAt').get(function wireCreatedAtVirtualType() {
+    return this.uploadDate;
+  });
+  FileSchema.virtual('updatedAt').get(function wireUpdateAtVirtualType() {
+    return this.uploadDate;
+  });
+
+  // allow virtuals to be included in toJSON and toObject
+  FileSchema.set('toJSON', { virtuals: true });
+  FileSchema.set('toObject', { virtuals: true });
+
+  // attach bucket instance
+  FileSchema.statics.bucket = bucket;
+
+  /* instances */
+
+  /**
+   * @function write
+   * @name write
+   * @description Write provided file into MongoDB GridFS
+   * @param {stream.Readable} stream readable stream
+   * @param {Function} [done] a callback to invoke in success or error
+   * @returns {object} Valid instance of mongoose model.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @instance
+   * @example
+   *
+   * const attachment = new Attachment({ filename });
+   * attachment.write(readablestream, (error, attached) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.methods.write = function write(stream, done) {
+    // obtain file writable details
+    const file = _.pick(copyInstance(this), WRITABLES);
+
+    // stream file to gridfs
+    return bucket.writeFile(
+      file,
+      stream,
+      function afterWriteFile(error, created) {
+        // back-off error
+        if (error) {
+          return done(error);
+        }
+        // read file details
+        // eslint-disable-next-line no-underscore-dangle
+        return this.constructor.findById(created._id, done);
+      }.bind(this)
+    );
+  };
+
+  /**
+   * @function read
+   * @name read
+   * @description Read file from MongoDB GridFS
+   * @param {object} optns valid criteria for read existing file.
+   * @param {number} [optns.revision=-1] The revision number relative to the
+   * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+   * the 2nd oldest, -1 gets you the newest.
+   * @param {number} [optns.start] Optional 0-based offset in bytes to start
+   * streaming from.
+   * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+   * streaming before.
+   * @param {Function} [done] a callback to invoke on success or error.
+   *
+   * Warn!: Pass callback if filesize is small enough.
+   * Otherwise consider using stream instead.
+   * @returns {object} a GridFSBucketReadStream instance.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @instance
+   * @example
+   *
+   * // small file
+   * Attachment.findById(_id, (error, attachment) => {
+   *   attachment.read((error, content) => { ... });
+   * });
+   *
+   * // large file
+   * Attachment.findById(_id, (error, attachment) => {
+   *   const readstream = attachment.read();
+   *   stream.on('error', fn);
+   *   stream.on('data', fn);
+   *   stream.on('close', fn);
+   * });
+   */
+  FileSchema.methods.read = function read(optns, done) {
+    // normalize arguments
+    let $optns = optns;
+    let cb = done;
+    if (_.isFunction(optns)) {
+      cb = optns;
+      $optns = {};
+    }
+
+    // stream file out of gridfs
+    const { _id } = this;
+    const { filename } = this;
+    const $$optns = _.merge({}, $optns, { _id, filename });
+    return bucket.readFile($$optns, cb);
+  };
+
+  /**
+   * @function unlink
+   * @name unlink
+   * @alias unlink
+   * @description Remove an existing file and its chunks.
+   * @param {Function} done a callback to invoke on success or error
+   * @returns {object} mongoose model instance
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @instance
+   * @example
+   *
+   * attachment.unlink((error, unlinked) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.methods.unlink = function unlink(done) {
+    // obtain file details
+    return this.constructor.findById(
+      // eslint-disable-next-line no-underscore-dangle
+      this._id,
+      function afterFindFile(error, file) {
+        // back-off error
+        if (error) {
+          return done(error);
+        }
+        // remove file from gridfs
+        return bucket.deleteFile(
+          // eslint-disable-next-line no-underscore-dangle
+          file._id,
+          function afterDeleteFile($error /* , id */) {
+            done($error, file);
+          }
+        );
+      }
+    );
+  };
+
+  /* statics */
+
+  /**
+   * @function
+   * @name write
+   * @description Write provided file into MongoDB GridFS
+   * @param {object} file valid file details
+   * @param {stream.Readable} stream readable stream
+   * @param {Function} [done] a callback to invoke in success or error
+   * @returns {object} a GridFSBucketWriteStream instance.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @static
+   * @public
+   * @example
+   *
+   * // large file
+   * const writeStream = Attachment.write({ filename }, readStream);
+   *
+   * // small file
+   * Attachment.write({ filename }, readstream, (error, file) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.statics.write = function write(file, stream, done) {
+    const $file = new this(file);
+    return $file.write(stream, done);
+  };
+
+  /**
+   * @function read
+   * @name read
+   * @description Read file from MongoDB GridFS
+   * @param {object} optns valid criteria for read existing file.
+   * @param {object} optns._id The id of the file doc
+   * @param {string} [optns.filename] The name of the file doc to stream
+   * @param {number} [optns.revision=-1] The revision number relative to the
+   * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+   * the 2nd oldest, -1 gets you the newest.
+   * @param {number} [optns.start] Optional 0-based offset in bytes to start
+   * streaming from.
+   * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+   * streaming before.
+   *
+   * Warn!: Pass callback if filesize is small enough.
+   * Otherwise consider using stream instead.
+   * @param {Function} [done] a callback to invoke on success or error
+   * @returns {object} a GridFSBucketReadStream instance.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @static
+   * @public
+   * @example
+   *
+   * // small file
+   * Attachment.read({ _id }, (error, content) => { ... });
+   *
+   * // large file
+   * const readstream = Attachment.read({ _id });
+   * stream.on('error', fn);
+   * stream.on('data', fn);
+   * stream.on('close', fn);
+   */
+  FileSchema.statics.read = function read(optns, done) {
+    return bucket.readFile(optns, done);
+  };
+
+  /**
+   * @function unlink
+   * @name unlink
+   * @alias unlink
+   * @description Remove an existing file and its chunks.
+   * @param {object} _id The id of the file doc
+   * @param {Function} done a callback to invoke on success or error
+   * @returns {object} mongoose model instance
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @static
+   * @public
+   * @example
+   *
+   * Attachment.unlink(_id, (error, unlinked) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.statics.unlink = function unlink(_id, done) {
+    return this.findById(_id, function afterFindById(error, file) {
+      // back-off error
+      if (error) {
+        return done(error);
+      }
+
+      if (!file) {
+        return done(new Error('not found'));
+      }
+
+      // remove file from gridfs
+      return file.unlink(done);
+    });
+  };
+
+  // return grifs schema
+  return FileSchema;
+}
+
+const { ObjectId } = MongooseTypes;
+
+/* constants */
+const DEFAULT_BUCKET_MODEL_NAME = 'File';
+const DEFAULT_BUCKET_NAME = 'fs';
+const DEFAULT_BUCKET_CHUNK_SIZE = 255 * 1024;
+const DEFAULT_BUCKET_OPTIONS = {
+  modelName: DEFAULT_BUCKET_MODEL_NAME,
+  bucketName: DEFAULT_BUCKET_NAME,
+  chunkSizeBytes: DEFAULT_BUCKET_CHUNK_SIZE,
+};
+
+/* getters */
+
+/**
+ * @name bucketName
+ * @description Bucket name used to prefix 'files' and 'chunks' collections.
+ * @returns {string}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const bucketName = bucket.bucketName;
+ * //=> fs
+ */
+Object.defineProperty(GridFSBucket.prototype, 'bucketName', {
+  get: function getBucketName() {
+    return this.s.options.bucketName;
+  },
+});
+
+/**
+ * @name collection
+ * @description Collection used to store file data.
+ * @returns {object} Valid mongodb collection
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.6.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const collection = bucket.collection;
+ * //=> Collection { ... }
+ */
+Object.defineProperty(GridFSBucket.prototype, 'collection', {
+  get: function getCollection() {
+    // eslint-disable-next-line no-underscore-dangle
+    return this.s._filesCollection;
+  },
+});
+
+/**
+ * @name collectionName
+ * @description Name of a collection used to store file.
+ * @returns {string} valid mongodb collection name
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const collectionName = bucket.collectionName;
+ * //=> fs.files
+ */
+Object.defineProperty(GridFSBucket.prototype, 'collectionName', {
+  get: function getCollectionName() {
+    // eslint-disable-next-line no-underscore-dangle
+    return this.s._filesCollection.s.namespace.collection;
+  },
+});
+
+/* streams */
+
+/**
+ * @function createWriteStream
+ * @name createWriteStream
+ * @description Creates a writable stream (GridFSBucketWriteStream) for writing
+ * buffers to GridFS for a custom file id. The stream's 'id' property contains
+ * the resulting file's id.
+ * @param {object} optns Valid options for write file.
+ * @param {ObjectId} [optns._id] A custom id used to identify file doc.
+ * @param {string} optns.filename The value of the 'filename' key in the files
+ * doc.
+ * @param {number} [optns.chunkSizeBytes] Optional overwrite this bucket's
+ * chunkSizeBytes for this file.
+ * @param {object} [optns.metadata] Optional object to store in the file
+ * document's `metadata` field.
+ * @param {string} [optns.contentType] Optional string to store in the file
+ * document's `contentType` field.
+ * @param {Array} [optns.aliases] Optional array of strings to store in the
+ * file document's `aliases` field.
+ * @param {boolean} [optns.disableMD5=false] If true, disables adding an
+ * md5 field to file data.
+ * @returns {object} Valid mongodb `GridFSBucketWriteStream`
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const _id = new ObjectId();
+ * const filename = 'filename.txt';
+ * const readStream = fs.createReadStream(filename);
+ * const writeStream = bucket.createWriteStream({_id, filename});
+ * readStream.pipe(writeStream);
+ */
+GridFSBucket.prototype.createWriteStream = function createWriteStream(optns) {
+  // ensure options
+  const defaults = { _id: new ObjectId() };
+  const options = _.merge({}, defaults, optns);
+  const { _id, filename } = options;
+
+  // ensure filename
+  if (_.isEmpty(filename)) {
+    const error = new Error('Missing filename');
+    error.status = 400;
+    throw error;
+  }
+
+  // open write stream
+  const writeStream = this.openUploadStreamWithId(_id, filename, options);
+
+  // return writeStream
+  return writeStream;
+};
+
+/**
+ * @function createReadStream
+ * @name createReadStream
+ * @description Creates a readable stream (GridFSBucketReadStream) for
+ * streaming the file with the given name from GridFS. If there are multiple
+ * files with the same name, this will stream the most recent file with the
+ * given name (as determined by the `uploadDate` field). You can set the
+ * `revision` option to change this behavior.
+ * @param {object} [optns] Valid options for read existing file.
+ * @param {ObjectId} optns._id The id of the file doc
+ * @param {string} [optns.filename] The name of the file doc to stream
+ * @param {number} [optns.revision=-1] The revision number relative to the
+ * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+ * the 2nd oldest, -1 gets you the newest.
+ * @param {number} [optns.start] Optional 0-based offset in bytes to start
+ * streaming from.
+ * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+ * streaming before.
+ * @returns {object} Valid mongodb `GridFSBucketReadStream`
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const _id = new ObjectId();
+ * const filename = 'filename.txt';
+ * const writeStream = fs.createWriteStream(filename);
+ * const readStream = bucket.createReadStream({_id, filename});
+ * readStream.pipe(writeStream);
+ */
+GridFSBucket.prototype.createReadStream = function createReadStream(optns) {
+  // ensure options
+  const options = _.merge({}, optns);
+  const { _id, filename } = options;
+
+  // ensure filename or _id
+  if (_.isEmpty(filename) && !_id) {
+    const error = Error('Missing filename or file id');
+    error.status = 400;
+    throw error;
+  }
+
+  // initalize file read stream
+  let readstream;
+
+  // open download stream by file id
+  if (_id) {
+    readstream = this.openDownloadStream(_id, options);
+  }
+
+  // open download stream by file name
+  if (!_.isEmpty(filename) && !readstream) {
+    readstream = this.openDownloadStreamByName(filename, options);
+  }
+
+  // return read stream
+  return readstream;
+};
+
+/* writers */
+
+/**
+ * @function writeFile
+ * @name writeFile
+ * @description Write provided file into MongoDB GridFS
+ * @param {object} file valid file details
+ * @param {object} readstream valid nodejs `ReadableStream`
+ * @param {Function} [done] a callback to invoke on success or error
+ * @fires GridFSBucketWriteStream#error
+ * @fires GridFSBucketWriteStream#finish
+ * @returns {object} Valid mongodb `GridFSBucketWriteStream` instance.
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+ * @see {@link http://mongodb.github.io/node-mongodb-native}
+ * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+ * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * // large file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * const readStream = fs.createReadStream(filename);
+ * const writeStream = bucket.writeFile({ filename }, readStream);
+ *
+ * // small file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * const readStream = fs.createReadStream(filename);
+ * bucket.writeFile({ filename }, readStream, (error, file) => { ... });
+ */
+GridFSBucket.prototype.writeFile = function writeFile(file, readstream, done) {
+  // ensure file details
+  const $file = _.merge({}, { _id: new ObjectId() }, file);
+
+  // create file write stream
+  const writestream = this.createWriteStream($file);
+
+  // stream file into mongodb gridfs bucket
+  readstream.pipe(writestream);
+
+  // work on the stream
+  if (done && _.isFunction(done)) {
+    // handle errors
+    writestream.on('error', function onWriteFileError(error) {
+      return done(error);
+    });
+
+    // finalize write
+    writestream.on('finish', function onWriteFileFinish($$file) {
+      return done(null, $$file);
+    });
+  }
+
+  // return writestream
+  return writestream;
+};
+
+/* readers */
+
+/**
+ * @function readFile
+ * @name readFile
+ * @description Read file from MongoDB GridFS
+ * @param {object} optns valid criteria for read existing file.
+ * @param {object} optns._id The id of the file doc
+ * @param {string} [optns.filename] The name of the file doc to stream
+ * @param {number} [optns.revision=-1] The revision number relative to the
+ * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+ * the 2nd oldest, -1 gets you the newest.
+ * @param {number} [optns.start] Optional 0-based offset in bytes to start
+ * streaming from.
+ * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+ * streaming before.
+ * @param {Function} [done] a callback to invoke on success or error.
+ *
+ * Warn!: Pass callback if filesize is small enough.
+ * Otherwise consider using stream instead.
+ * @fires GridFSBucketReadStream#error
+ * @fires GridFSBucketReadStream#file
+ * @returns {object} Valid mongodb `GridFSBucketReadStream` instance.
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+ * @see {@link http://mongodb.github.io/node-mongodb-native}
+ * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+ * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * // large file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * const readStream = bucket.readFile({ filename });
+ *
+ * // small file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * bucket.readFile({ filename }, (error, buffer) => { ... });
+ */
+GridFSBucket.prototype.readFile = function readFile(optns, done) {
+  // ensure options
+  const $optns = _.merge({}, optns);
+
+  // create file read stream
+  const readstream = this.createReadStream($optns);
+
+  // pipe the whole stream into buffer if callback provided
+  if (done && _.isFunction(done)) {
+    return read(readstream, done);
+  }
+
+  // return stream
+
+  return readstream;
+};
+
+/* removers */
+
+/**
+ * @function deleteFile
+ * @name deleteFile
+ * @alias unlink
+ * @description Remove an existing file and its chunks.
+ * @param {ObjectId} _id The id of the file doc
+ * @param {Function} done a callback to invoke on success or error
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * bucket.deleteFile(_id, (error, results) => { ... });
+ */
+GridFSBucket.prototype.deleteFile = function deleteFile(_id, done) {
+  this.delete(_id, function afterDelete(error) {
+    return done(error, _id);
+  });
+};
+
+GridFSBucket.prototype.unlink = GridFSBucket.prototype.deleteFile;
+
+/* finders */
+
+/**
+ * @function findOne
+ * @name findOne
+ * @description find an existing file using options provided
+ * @param {object} optns valid find criteria
+ * @param {Function} done a callback to invoke on success or error
+ * @returns {object} existing file details
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * bucket.findOne({ _id }, (error, file) => { ... });
+ * bucket.findOne({ filename }, (error, file) => { ... });
+ */
+GridFSBucket.prototype.findOne = function findOne(optns, done) {
+  // ensure file find criteria
+  const options = _.merge({}, optns);
+
+  // find one existing file
+  try {
+    const cursor = this.find(options, { limit: 1 });
+    if (!cursor) {
+      const error = new Error('Collection not found');
+      error.status = 400;
+      return done(error);
+    }
+    return cursor.next(done);
+  } catch (error) {
+    // catch find errors
+    return done(error);
+  }
+};
+
+/**
+ * @function findById
+ * @name findById
+ * @description find an existing file with given objectid
+ * @param {ObjectId} _id valid objectid of the existing file
+ * @param {Function} done a callback to invoke on success or error
+ * @returns {object} existing file details
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * bucket.findById(_id, (error, file) => { ... });
+ */
+GridFSBucket.prototype.findById = function findById(_id, done) {
+  return this.findOne({ _id }, done);
+};
+
+/* multer */
+
+/**
+ * @function _handleFile
+ * @name _handleFile
+ * @description write file to the bucket and return information on how to
+ * access the file in the future
+ * @param {object} request injected request from multer
+ * @param {object} file injected file object from multer
+ * @param {Function} done a callback to invoke on success or error
+ * @author lally elias <lallyelias87@mail.com>
+ * @see {@link https://github.com/expressjs/multer/blob/master/StorageEngine.md}
+ * @since 0.1.0
+ * @version 0.5.0
+ * @instance
+ * @example
+ *
+ * const express = require('express');
+ * const multer  = require('multer');
+ * const { createBucket } = require('mongoose-gridfs');
+ * const app = express();
+ * const storage = createBucket(); // createBucket(optns)
+ * const upload = multer({ storage });
+ *
+ * app.post('/profile', upload.single('avatar'), (req, res, next) => {
+ *   // req.file is the `avatar` file
+ *   // req.body contains the text fields
+ * });
+ */
+// eslint-disable-next-line no-underscore-dangle
+GridFSBucket.prototype._handleFile = function _handleFile(request, file, done) {
+  // obtain file readable stream
+  const { stream } = file;
+
+  // prepare file details
+  const { aliases } = request.body || {};
+  const $file = _.merge(
+    {},
+    {
+      _id: new ObjectId(),
+      filename: file.originalname,
+      contentType: file.mimetype,
+      aliases: aliases ? [].concat(aliases) : aliases,
+      metadata: (request.body || {}).metadata,
+    }
+  );
+
+  // obtain bucket details
+  const { bucketName } = this;
+
+  // write file
+  this.writeFile($file, stream, function afterHandleFile(error, $$file) {
+    if ($$file) {
+      // eslint-disable-next-line no-param-reassign
+      $$file.size = $$file.size || $$file.length;
+      // eslint-disable-next-line no-param-reassign
+      $$file.bucketName = bucketName;
+    }
+    return done(error, $$file);
+  });
+};
+
+/**
+ * @function _removeFile
+ * @name _removeFile
+ * @description remove existing file from bucket
+ * @param {object} request injected request from multer
+ * @param {object} file injected file object from multer
+ * @param {Function} done a callback to invoke on success or error
+ * @returns {object|Error} error or deleted file
+ * @author lally elias <lallyelias87@mail.com>
+ * @see {@link https://github.com/expressjs/multer/blob/master/StorageEngine.md}
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const express = require('express');
+ * const multer  = require('multer');
+ * const { createBucket } = require('mongoose-gridfs');
+ * const app = express();
+ * const storage = createBucket(); // createBucket(optns)
+ * const upload = multer({ storage });
+ *
+ * app.post('/profile', upload.single('avatar'), (req, res, next) => {
+ *   // req.file is the `avatar` file
+ *   // req.body contains the text fields
+ * });
+ */
+// eslint-disable-next-line no-underscore-dangle
+GridFSBucket.prototype._removeFile = function _removeFile(request, file, done) {
+  // remove file
+  // eslint-disable-next-line no-underscore-dangle
+  if (file._id) {
+    // eslint-disable-next-line no-underscore-dangle
+    return this.deleteFile(file._id, done);
+  }
+  // no operation
+
+  return done(null, null);
+};
+
+/* statics */
+
+/**
+ * @function createBucket
+ * @name createBucket
+ * @description Create GridFSBucket
+ * @param {object} [optns] Optional settings.
+ * @param {object} [optns.connection = mongoose.connection] A valid
+ * instance of mongoose connection.
+ * @param {string} [optns.bucketName="fs"] The 'files' and 'chunks' collections
+ * will be prefixed with the bucket name followed by a dot.
+ * @param {number} [optns.chunkSizeBytes=255 * 1024] Number of bytes stored in
+ * each chunk. Defaults to 255KB
+ * @param {object} [optns.writeConcern] Optional write concern to be passed to
+ * write operations, for instance `{ w: 1 }`
+ * @param {object} [optns.readPreference] Optional read preference to be passed
+ * to read operations
+ * @returns {object} an instance of `GridFSBucket`
+ * @author lally elias <lallyelias87@mail.com>
+ * @since 1.0.0
+ * @version 0.1.0
+ * @public
+ * @static
+ * @example
+ *
+ * const bucket = createBucket();
+ * const bucket = createBucket({ bucketName });
+ * const bucket = createBucket({ buketName, connection });
+ */
+function createBucket(optns = {}) {
+  // ensure options
+  let { connection } = optns;
+  connection = connection || mongoose.connection;
+  const options = _.merge(
+    {},
+    DEFAULT_BUCKET_OPTIONS,
+    _.omit(optns, 'connection')
+  );
+
+  // create GridFSBucket
+  const { db } = connection;
+  const bucket = new GridFSBucket(db, options);
+
+  // return bucket
+  return bucket;
+}
+
+/**
+ * @function createModel
+ * @name createModel
+ * @description Create GridFSBucket files collection model
+ * @param {object} [optns] Optional settings.
+ * @param {object} [optns.connection = mongoose.connection] A valid instance
+ * of mongoose connection.
+ * @param {string} [optns.modelName="File"] Valid model name to use with
+ * mongoose
+ * @param {string} [optns.bucketName="fs"] The 'files' and 'chunks' collections
+ * will be prefixed with the bucket name followed by a dot.
+ * @param {number} [optns.chunkSizeBytes=255 * 1024] Number of bytes stored in
+ * each chunk. Defaults to 255KB
+ * @param {object} [optns.writeConcern] Optional write concern to be passed to
+ * write operations, for instance `{ w: 1 }`
+ * @param {object} [optns.readPreference] Optional read preference to be passed
+ * to read operations
+ * @param {...Function} [plugins] list of valid mongoose plugin to apply to
+ * file schema
+ * @returns {object} an instance of `GridFSBucket`
+ * @author lally elias <lallyelias87@mail.com>
+ * @since 1.0.0
+ * @version 0.2.0
+ * @public
+ * @static
+ * @example
+ *
+ * const File = createModel(); // => fs.files
+ * const Photo = createModel({ modelName }); // => photos.files
+ * const Photo = createModel({ modelName, connection }); // => photos.files
+ */
+function createModel(optns, ...plugins) {
+  // ensure options
+  let { connection, modelName, bucketName } = _.merge({}, optns);
+  connection = connection || mongoose.connection;
+  modelName = _.isEmpty(modelName) ? DEFAULT_BUCKET_MODEL_NAME : modelName;
+  bucketName = toCollectionName(modelName);
+  bucketName =
+    modelName === DEFAULT_BUCKET_MODEL_NAME ? DEFAULT_BUCKET_NAME : bucketName;
+
+  // create bucket
+  const options = _.merge({}, { connection, modelName, bucketName }, optns);
+  const bucket = createBucket(options);
+
+  // construct file schema
+  const schema = createFileSchema(bucket);
+
+  // apply schema plugins with model options
+  const schemaOptions = _.merge({}, schema.options);
+  _.forEach([...plugins], (plugin) => {
+    schema.plugin(plugin, schemaOptions);
+  });
+
+  // hack(to be removed): fake timestamp fields
+  schema.statics.CREATED_AT_FIELD = 'uploadDate';
+  schema.statics.UPDATED_AT_FIELD = 'uploadDate';
+
+  // compile file model
+  const fileModel = model(modelName, schema, connection);
+
+  // return model
+  return fileModel;
+}
+
+export { DEFAULT_BUCKET_CHUNK_SIZE, DEFAULT_BUCKET_MODEL_NAME, DEFAULT_BUCKET_NAME, DEFAULT_BUCKET_OPTIONS, createBucket, createModel };
diff --git a/lib/index.js b/lib/index.js
new file mode 100644
index 0000000..9488a35
--- /dev/null
+++ b/lib/index.js
@@ -0,0 +1,952 @@
+'use strict';
+
+const _ = require('lodash');
+const read = require('stream-read');
+const mongoose = require('mongoose');
+const mongooseCommon = require('@lykmapipo/mongoose-common');
+
+/* constants */
+const WRITABLES = ['_id', 'filename', 'contentType', 'aliases', 'metadata'];
+
+/**
+ * @function createFileSchema
+ * @name createFileSchema
+ * @description Create mongoose schema compactible with gridfs files collection.
+ * @param {object} bucket Valid instance of `GridFSBucket`
+ * @returns {object} valid mongoose schema to access specific gridfs
+ * files collection.
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/#the-files-collection}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @private
+ */
+function createFileSchema(bucket) {
+  // obtain collection name from bucket
+  const collection = bucket.collectionName;
+
+  // gridfs files collection compactible schema
+  // see https://docs.mongodb.com/manual/core/gridfs/#the-files-collection
+  const FileSchema = new mongooseCommon.Schema(
+    {
+      length: { type: Number, index: true },
+      chunkSize: { type: Number, index: true },
+      uploadDate: { type: Date, index: true },
+      md5: { type: String, trim: true, index: true, searchable: true },
+      filename: { type: String, trim: true, index: true, searchable: true },
+      contentType: { type: String, trim: true, index: true, searchable: true },
+      aliases: { type: [String], sort: true, index: true, searchable: true },
+      metadata: { type: mongooseCommon.Mixed },
+    },
+    { collection, id: false, emitIndexErrors: true }
+  );
+
+  // expose timestamps as virtuals
+  FileSchema.virtual('createdAt').get(function wireCreatedAtVirtualType() {
+    return this.uploadDate;
+  });
+  FileSchema.virtual('updatedAt').get(function wireUpdateAtVirtualType() {
+    return this.uploadDate;
+  });
+
+  // allow virtuals to be included in toJSON and toObject
+  FileSchema.set('toJSON', { virtuals: true });
+  FileSchema.set('toObject', { virtuals: true });
+
+  // attach bucket instance
+  FileSchema.statics.bucket = bucket;
+
+  /* instances */
+
+  /**
+   * @function write
+   * @name write
+   * @description Write provided file into MongoDB GridFS
+   * @param {stream.Readable} stream readable stream
+   * @param {Function} [done] a callback to invoke in success or error
+   * @returns {object} Valid instance of mongoose model.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @instance
+   * @example
+   *
+   * const attachment = new Attachment({ filename });
+   * attachment.write(readablestream, (error, attached) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.methods.write = function write(stream, done) {
+    // obtain file writable details
+    const file = _.pick(mongooseCommon.copyInstance(this), WRITABLES);
+
+    // stream file to gridfs
+    return bucket.writeFile(
+      file,
+      stream,
+      function afterWriteFile(error, created) {
+        // back-off error
+        if (error) {
+          return done(error);
+        }
+        // read file details
+        // eslint-disable-next-line no-underscore-dangle
+        return this.constructor.findById(created._id, done);
+      }.bind(this)
+    );
+  };
+
+  /**
+   * @function read
+   * @name read
+   * @description Read file from MongoDB GridFS
+   * @param {object} optns valid criteria for read existing file.
+   * @param {number} [optns.revision=-1] The revision number relative to the
+   * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+   * the 2nd oldest, -1 gets you the newest.
+   * @param {number} [optns.start] Optional 0-based offset in bytes to start
+   * streaming from.
+   * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+   * streaming before.
+   * @param {Function} [done] a callback to invoke on success or error.
+   *
+   * Warn!: Pass callback if filesize is small enough.
+   * Otherwise consider using stream instead.
+   * @returns {object} a GridFSBucketReadStream instance.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @instance
+   * @example
+   *
+   * // small file
+   * Attachment.findById(_id, (error, attachment) => {
+   *   attachment.read((error, content) => { ... });
+   * });
+   *
+   * // large file
+   * Attachment.findById(_id, (error, attachment) => {
+   *   const readstream = attachment.read();
+   *   stream.on('error', fn);
+   *   stream.on('data', fn);
+   *   stream.on('close', fn);
+   * });
+   */
+  FileSchema.methods.read = function read(optns, done) {
+    // normalize arguments
+    let $optns = optns;
+    let cb = done;
+    if (_.isFunction(optns)) {
+      cb = optns;
+      $optns = {};
+    }
+
+    // stream file out of gridfs
+    const { _id } = this;
+    const { filename } = this;
+    const $$optns = _.merge({}, $optns, { _id, filename });
+    return bucket.readFile($$optns, cb);
+  };
+
+  /**
+   * @function unlink
+   * @name unlink
+   * @alias unlink
+   * @description Remove an existing file and its chunks.
+   * @param {Function} done a callback to invoke on success or error
+   * @returns {object} mongoose model instance
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @instance
+   * @example
+   *
+   * attachment.unlink((error, unlinked) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.methods.unlink = function unlink(done) {
+    // obtain file details
+    return this.constructor.findById(
+      // eslint-disable-next-line no-underscore-dangle
+      this._id,
+      function afterFindFile(error, file) {
+        // back-off error
+        if (error) {
+          return done(error);
+        }
+        // remove file from gridfs
+        return bucket.deleteFile(
+          // eslint-disable-next-line no-underscore-dangle
+          file._id,
+          function afterDeleteFile($error /* , id */) {
+            done($error, file);
+          }
+        );
+      }
+    );
+  };
+
+  /* statics */
+
+  /**
+   * @function
+   * @name write
+   * @description Write provided file into MongoDB GridFS
+   * @param {object} file valid file details
+   * @param {stream.Readable} stream readable stream
+   * @param {Function} [done] a callback to invoke in success or error
+   * @returns {object} a GridFSBucketWriteStream instance.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @static
+   * @public
+   * @example
+   *
+   * // large file
+   * const writeStream = Attachment.write({ filename }, readStream);
+   *
+   * // small file
+   * Attachment.write({ filename }, readstream, (error, file) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.statics.write = function write(file, stream, done) {
+    const $file = new this(file);
+    return $file.write(stream, done);
+  };
+
+  /**
+   * @function read
+   * @name read
+   * @description Read file from MongoDB GridFS
+   * @param {object} optns valid criteria for read existing file.
+   * @param {object} optns._id The id of the file doc
+   * @param {string} [optns.filename] The name of the file doc to stream
+   * @param {number} [optns.revision=-1] The revision number relative to the
+   * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+   * the 2nd oldest, -1 gets you the newest.
+   * @param {number} [optns.start] Optional 0-based offset in bytes to start
+   * streaming from.
+   * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+   * streaming before.
+   *
+   * Warn!: Pass callback if filesize is small enough.
+   * Otherwise consider using stream instead.
+   * @param {Function} [done] a callback to invoke on success or error
+   * @returns {object} a GridFSBucketReadStream instance.
+   * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+   * @see {@link http://mongodb.github.io/node-mongodb-native}
+   * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+   * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @static
+   * @public
+   * @example
+   *
+   * // small file
+   * Attachment.read({ _id }, (error, content) => { ... });
+   *
+   * // large file
+   * const readstream = Attachment.read({ _id });
+   * stream.on('error', fn);
+   * stream.on('data', fn);
+   * stream.on('close', fn);
+   */
+  FileSchema.statics.read = function read(optns, done) {
+    return bucket.readFile(optns, done);
+  };
+
+  /**
+   * @function unlink
+   * @name unlink
+   * @alias unlink
+   * @description Remove an existing file and its chunks.
+   * @param {object} _id The id of the file doc
+   * @param {Function} done a callback to invoke on success or error
+   * @returns {object} mongoose model instance
+   * @author lally elias <lallyelias87@mail.com>
+   * @license MIT
+   * @since 1.0.0
+   * @version 0.1.0
+   * @static
+   * @public
+   * @example
+   *
+   * Attachment.unlink(_id, (error, unlinked) => {
+   *  //=> {_id: ..., filename: ..., ... }
+   * });
+   */
+  FileSchema.statics.unlink = function unlink(_id, done) {
+    return this.findById(_id, function afterFindById(error, file) {
+      // back-off error
+      if (error) {
+        return done(error);
+      }
+
+      if (!file) {
+        return done(new Error('not found'));
+      }
+
+      // remove file from gridfs
+      return file.unlink(done);
+    });
+  };
+
+  // return grifs schema
+  return FileSchema;
+}
+
+const { ObjectId } = mongooseCommon.MongooseTypes;
+
+/* constants */
+const DEFAULT_BUCKET_MODEL_NAME = 'File';
+const DEFAULT_BUCKET_NAME = 'fs';
+const DEFAULT_BUCKET_CHUNK_SIZE = 255 * 1024;
+const DEFAULT_BUCKET_OPTIONS = {
+  modelName: DEFAULT_BUCKET_MODEL_NAME,
+  bucketName: DEFAULT_BUCKET_NAME,
+  chunkSizeBytes: DEFAULT_BUCKET_CHUNK_SIZE,
+};
+
+/* getters */
+
+/**
+ * @name bucketName
+ * @description Bucket name used to prefix 'files' and 'chunks' collections.
+ * @returns {string}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const bucketName = bucket.bucketName;
+ * //=> fs
+ */
+Object.defineProperty(mongooseCommon.GridFSBucket.prototype, 'bucketName', {
+  get: function getBucketName() {
+    return this.s.options.bucketName;
+  },
+});
+
+/**
+ * @name collection
+ * @description Collection used to store file data.
+ * @returns {object} Valid mongodb collection
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.6.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const collection = bucket.collection;
+ * //=> Collection { ... }
+ */
+Object.defineProperty(mongooseCommon.GridFSBucket.prototype, 'collection', {
+  get: function getCollection() {
+    // eslint-disable-next-line no-underscore-dangle
+    return this.s._filesCollection;
+  },
+});
+
+/**
+ * @name collectionName
+ * @description Name of a collection used to store file.
+ * @returns {string} valid mongodb collection name
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const collectionName = bucket.collectionName;
+ * //=> fs.files
+ */
+Object.defineProperty(mongooseCommon.GridFSBucket.prototype, 'collectionName', {
+  get: function getCollectionName() {
+    // eslint-disable-next-line no-underscore-dangle
+    return this.s._filesCollection.s.namespace.collection;
+  },
+});
+
+/* streams */
+
+/**
+ * @function createWriteStream
+ * @name createWriteStream
+ * @description Creates a writable stream (GridFSBucketWriteStream) for writing
+ * buffers to GridFS for a custom file id. The stream's 'id' property contains
+ * the resulting file's id.
+ * @param {object} optns Valid options for write file.
+ * @param {ObjectId} [optns._id] A custom id used to identify file doc.
+ * @param {string} optns.filename The value of the 'filename' key in the files
+ * doc.
+ * @param {number} [optns.chunkSizeBytes] Optional overwrite this bucket's
+ * chunkSizeBytes for this file.
+ * @param {object} [optns.metadata] Optional object to store in the file
+ * document's `metadata` field.
+ * @param {string} [optns.contentType] Optional string to store in the file
+ * document's `contentType` field.
+ * @param {Array} [optns.aliases] Optional array of strings to store in the
+ * file document's `aliases` field.
+ * @param {boolean} [optns.disableMD5=false] If true, disables adding an
+ * md5 field to file data.
+ * @returns {object} Valid mongodb `GridFSBucketWriteStream`
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const _id = new ObjectId();
+ * const filename = 'filename.txt';
+ * const readStream = fs.createReadStream(filename);
+ * const writeStream = bucket.createWriteStream({_id, filename});
+ * readStream.pipe(writeStream);
+ */
+mongooseCommon.GridFSBucket.prototype.createWriteStream = function createWriteStream(optns) {
+  // ensure options
+  const defaults = { _id: new ObjectId() };
+  const options = _.merge({}, defaults, optns);
+  const { _id, filename } = options;
+
+  // ensure filename
+  if (_.isEmpty(filename)) {
+    const error = new Error('Missing filename');
+    error.status = 400;
+    throw error;
+  }
+
+  // open write stream
+  const writeStream = this.openUploadStreamWithId(_id, filename, options);
+
+  // return writeStream
+  return writeStream;
+};
+
+/**
+ * @function createReadStream
+ * @name createReadStream
+ * @description Creates a readable stream (GridFSBucketReadStream) for
+ * streaming the file with the given name from GridFS. If there are multiple
+ * files with the same name, this will stream the most recent file with the
+ * given name (as determined by the `uploadDate` field). You can set the
+ * `revision` option to change this behavior.
+ * @param {object} [optns] Valid options for read existing file.
+ * @param {ObjectId} optns._id The id of the file doc
+ * @param {string} [optns.filename] The name of the file doc to stream
+ * @param {number} [optns.revision=-1] The revision number relative to the
+ * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+ * the 2nd oldest, -1 gets you the newest.
+ * @param {number} [optns.start] Optional 0-based offset in bytes to start
+ * streaming from.
+ * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+ * streaming before.
+ * @returns {object} Valid mongodb `GridFSBucketReadStream`
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * const _id = new ObjectId();
+ * const filename = 'filename.txt';
+ * const writeStream = fs.createWriteStream(filename);
+ * const readStream = bucket.createReadStream({_id, filename});
+ * readStream.pipe(writeStream);
+ */
+mongooseCommon.GridFSBucket.prototype.createReadStream = function createReadStream(optns) {
+  // ensure options
+  const options = _.merge({}, optns);
+  const { _id, filename } = options;
+
+  // ensure filename or _id
+  if (_.isEmpty(filename) && !_id) {
+    const error = Error('Missing filename or file id');
+    error.status = 400;
+    throw error;
+  }
+
+  // initalize file read stream
+  let readstream;
+
+  // open download stream by file id
+  if (_id) {
+    readstream = this.openDownloadStream(_id, options);
+  }
+
+  // open download stream by file name
+  if (!_.isEmpty(filename) && !readstream) {
+    readstream = this.openDownloadStreamByName(filename, options);
+  }
+
+  // return read stream
+  return readstream;
+};
+
+/* writers */
+
+/**
+ * @function writeFile
+ * @name writeFile
+ * @description Write provided file into MongoDB GridFS
+ * @param {object} file valid file details
+ * @param {object} readstream valid nodejs `ReadableStream`
+ * @param {Function} [done] a callback to invoke on success or error
+ * @fires GridFSBucketWriteStream#error
+ * @fires GridFSBucketWriteStream#finish
+ * @returns {object} Valid mongodb `GridFSBucketWriteStream` instance.
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+ * @see {@link http://mongodb.github.io/node-mongodb-native}
+ * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+ * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * // large file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * const readStream = fs.createReadStream(filename);
+ * const writeStream = bucket.writeFile({ filename }, readStream);
+ *
+ * // small file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * const readStream = fs.createReadStream(filename);
+ * bucket.writeFile({ filename }, readStream, (error, file) => { ... });
+ */
+mongooseCommon.GridFSBucket.prototype.writeFile = function writeFile(file, readstream, done) {
+  // ensure file details
+  const $file = _.merge({}, { _id: new ObjectId() }, file);
+
+  // create file write stream
+  const writestream = this.createWriteStream($file);
+
+  // stream file into mongodb gridfs bucket
+  readstream.pipe(writestream);
+
+  // work on the stream
+  if (done && _.isFunction(done)) {
+    // handle errors
+    writestream.on('error', function onWriteFileError(error) {
+      return done(error);
+    });
+
+    // finalize write
+    writestream.on('finish', function onWriteFileFinish($$file) {
+      return done(null, $$file);
+    });
+  }
+
+  // return writestream
+  return writestream;
+};
+
+/* readers */
+
+/**
+ * @function readFile
+ * @name readFile
+ * @description Read file from MongoDB GridFS
+ * @param {object} optns valid criteria for read existing file.
+ * @param {object} optns._id The id of the file doc
+ * @param {string} [optns.filename] The name of the file doc to stream
+ * @param {number} [optns.revision=-1] The revision number relative to the
+ * oldest file with the given filename. 0 gets you the oldest file, 1 gets you
+ * the 2nd oldest, -1 gets you the newest.
+ * @param {number} [optns.start] Optional 0-based offset in bytes to start
+ * streaming from.
+ * @param {number} [optns.end] Optional 0-based offset in bytes to stop
+ * streaming before.
+ * @param {Function} [done] a callback to invoke on success or error.
+ *
+ * Warn!: Pass callback if filesize is small enough.
+ * Otherwise consider using stream instead.
+ * @fires GridFSBucketReadStream#error
+ * @fires GridFSBucketReadStream#file
+ * @returns {object} Valid mongodb `GridFSBucketReadStream` instance.
+ * @see {@link https://docs.mongodb.com/manual/core/gridfs/}
+ * @see {@link http://mongodb.github.io/node-mongodb-native}
+ * @see {@link https://nodejs.org/api/stream.html#stream_writable_streams}
+ * @see {@link https://nodejs.org/api/stream.html#stream_readable_streams}
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * // large file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * const readStream = bucket.readFile({ filename });
+ *
+ * // small file
+ * const bucket = createBucket();
+ * const filename = 'filename.txt';
+ * bucket.readFile({ filename }, (error, buffer) => { ... });
+ */
+mongooseCommon.GridFSBucket.prototype.readFile = function readFile(optns, done) {
+  // ensure options
+  const $optns = _.merge({}, optns);
+
+  // create file read stream
+  const readstream = this.createReadStream($optns);
+
+  // pipe the whole stream into buffer if callback provided
+  if (done && _.isFunction(done)) {
+    return read(readstream, done);
+  }
+
+  // return stream
+
+  return readstream;
+};
+
+/* removers */
+
+/**
+ * @function deleteFile
+ * @name deleteFile
+ * @alias unlink
+ * @description Remove an existing file and its chunks.
+ * @param {ObjectId} _id The id of the file doc
+ * @param {Function} done a callback to invoke on success or error
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 1.0.0
+ * @version 0.1.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * bucket.deleteFile(_id, (error, results) => { ... });
+ */
+mongooseCommon.GridFSBucket.prototype.deleteFile = function deleteFile(_id, done) {
+  this.delete(_id, function afterDelete(error) {
+    return done(error, _id);
+  });
+};
+
+mongooseCommon.GridFSBucket.prototype.unlink = mongooseCommon.GridFSBucket.prototype.deleteFile;
+
+/* finders */
+
+/**
+ * @function findOne
+ * @name findOne
+ * @description find an existing file using options provided
+ * @param {object} optns valid find criteria
+ * @param {Function} done a callback to invoke on success or error
+ * @returns {object} existing file details
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * bucket.findOne({ _id }, (error, file) => { ... });
+ * bucket.findOne({ filename }, (error, file) => { ... });
+ */
+mongooseCommon.GridFSBucket.prototype.findOne = function findOne(optns, done) {
+  // ensure file find criteria
+  const options = _.merge({}, optns);
+
+  // find one existing file
+  try {
+    const cursor = this.find(options, { limit: 1 });
+    if (!cursor) {
+      const error = new Error('Collection not found');
+      error.status = 400;
+      return done(error);
+    }
+    return cursor.next(done);
+  } catch (error) {
+    // catch find errors
+    return done(error);
+  }
+};
+
+/**
+ * @function findById
+ * @name findById
+ * @description find an existing file with given objectid
+ * @param {ObjectId} _id valid objectid of the existing file
+ * @param {Function} done a callback to invoke on success or error
+ * @returns {object} existing file details
+ * @author lally elias <lallyelias87@mail.com>
+ * @license MIT
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const bucket = createBucket();
+ * bucket.findById(_id, (error, file) => { ... });
+ */
+mongooseCommon.GridFSBucket.prototype.findById = function findById(_id, done) {
+  return this.findOne({ _id }, done);
+};
+
+/* multer */
+
+/**
+ * @function _handleFile
+ * @name _handleFile
+ * @description write file to the bucket and return information on how to
+ * access the file in the future
+ * @param {object} request injected request from multer
+ * @param {object} file injected file object from multer
+ * @param {Function} done a callback to invoke on success or error
+ * @author lally elias <lallyelias87@mail.com>
+ * @see {@link https://github.com/expressjs/multer/blob/master/StorageEngine.md}
+ * @since 0.1.0
+ * @version 0.5.0
+ * @instance
+ * @example
+ *
+ * const express = require('express');
+ * const multer  = require('multer');
+ * const { createBucket } = require('mongoose-gridfs');
+ * const app = express();
+ * const storage = createBucket(); // createBucket(optns)
+ * const upload = multer({ storage });
+ *
+ * app.post('/profile', upload.single('avatar'), (req, res, next) => {
+ *   // req.file is the `avatar` file
+ *   // req.body contains the text fields
+ * });
+ */
+// eslint-disable-next-line no-underscore-dangle
+mongooseCommon.GridFSBucket.prototype._handleFile = function _handleFile(request, file, done) {
+  // obtain file readable stream
+  const { stream } = file;
+
+  // prepare file details
+  const { aliases } = request.body || {};
+  const $file = _.merge(
+    {},
+    {
+      _id: new ObjectId(),
+      filename: file.originalname,
+      contentType: file.mimetype,
+      aliases: aliases ? [].concat(aliases) : aliases,
+      metadata: (request.body || {}).metadata,
+    }
+  );
+
+  // obtain bucket details
+  const { bucketName } = this;
+
+  // write file
+  this.writeFile($file, stream, function afterHandleFile(error, $$file) {
+    if ($$file) {
+      // eslint-disable-next-line no-param-reassign
+      $$file.size = $$file.size || $$file.length;
+      // eslint-disable-next-line no-param-reassign
+      $$file.bucketName = bucketName;
+    }
+    return done(error, $$file);
+  });
+};
+
+/**
+ * @function _removeFile
+ * @name _removeFile
+ * @description remove existing file from bucket
+ * @param {object} request injected request from multer
+ * @param {object} file injected file object from multer
+ * @param {Function} done a callback to invoke on success or error
+ * @returns {object|Error} error or deleted file
+ * @author lally elias <lallyelias87@mail.com>
+ * @see {@link https://github.com/expressjs/multer/blob/master/StorageEngine.md}
+ * @since 0.1.0
+ * @version 0.7.0
+ * @instance
+ * @example
+ *
+ * const express = require('express');
+ * const multer  = require('multer');
+ * const { createBucket } = require('mongoose-gridfs');
+ * const app = express();
+ * const storage = createBucket(); // createBucket(optns)
+ * const upload = multer({ storage });
+ *
+ * app.post('/profile', upload.single('avatar'), (req, res, next) => {
+ *   // req.file is the `avatar` file
+ *   // req.body contains the text fields
+ * });
+ */
+// eslint-disable-next-line no-underscore-dangle
+mongooseCommon.GridFSBucket.prototype._removeFile = function _removeFile(request, file, done) {
+  // remove file
+  // eslint-disable-next-line no-underscore-dangle
+  if (file._id) {
+    // eslint-disable-next-line no-underscore-dangle
+    return this.deleteFile(file._id, done);
+  }
+  // no operation
+
+  return done(null, null);
+};
+
+/* statics */
+
+/**
+ * @function createBucket
+ * @name createBucket
+ * @description Create GridFSBucket
+ * @param {object} [optns] Optional settings.
+ * @param {object} [optns.connection = mongoose.connection] A valid
+ * instance of mongoose connection.
+ * @param {string} [optns.bucketName="fs"] The 'files' and 'chunks' collections
+ * will be prefixed with the bucket name followed by a dot.
+ * @param {number} [optns.chunkSizeBytes=255 * 1024] Number of bytes stored in
+ * each chunk. Defaults to 255KB
+ * @param {object} [optns.writeConcern] Optional write concern to be passed to
+ * write operations, for instance `{ w: 1 }`
+ * @param {object} [optns.readPreference] Optional read preference to be passed
+ * to read operations
+ * @returns {object} an instance of `GridFSBucket`
+ * @author lally elias <lallyelias87@mail.com>
+ * @since 1.0.0
+ * @version 0.1.0
+ * @public
+ * @static
+ * @example
+ *
+ * const bucket = createBucket();
+ * const bucket = createBucket({ bucketName });
+ * const bucket = createBucket({ buketName, connection });
+ */
+function createBucket(optns = {}) {
+  // ensure options
+  let { connection } = optns;
+  connection = connection || mongoose.connection;
+  const options = _.merge(
+    {},
+    DEFAULT_BUCKET_OPTIONS,
+    _.omit(optns, 'connection')
+  );
+
+  // create GridFSBucket
+  const { db } = connection;
+  const bucket = new mongooseCommon.GridFSBucket(db, options);
+
+  // return bucket
+  return bucket;
+}
+
+/**
+ * @function createModel
+ * @name createModel
+ * @description Create GridFSBucket files collection model
+ * @param {object} [optns] Optional settings.
+ * @param {object} [optns.connection = mongoose.connection] A valid instance
+ * of mongoose connection.
+ * @param {string} [optns.modelName="File"] Valid model name to use with
+ * mongoose
+ * @param {string} [optns.bucketName="fs"] The 'files' and 'chunks' collections
+ * will be prefixed with the bucket name followed by a dot.
+ * @param {number} [optns.chunkSizeBytes=255 * 1024] Number of bytes stored in
+ * each chunk. Defaults to 255KB
+ * @param {object} [optns.writeConcern] Optional write concern to be passed to
+ * write operations, for instance `{ w: 1 }`
+ * @param {object} [optns.readPreference] Optional read preference to be passed
+ * to read operations
+ * @param {...Function} [plugins] list of valid mongoose plugin to apply to
+ * file schema
+ * @returns {object} an instance of `GridFSBucket`
+ * @author lally elias <lallyelias87@mail.com>
+ * @since 1.0.0
+ * @version 0.2.0
+ * @public
+ * @static
+ * @example
+ *
+ * const File = createModel(); // => fs.files
+ * const Photo = createModel({ modelName }); // => photos.files
+ * const Photo = createModel({ modelName, connection }); // => photos.files
+ */
+function createModel(optns, ...plugins) {
+  // ensure options
+  let { connection, modelName, bucketName } = _.merge({}, optns);
+  connection = connection || mongoose.connection;
+  modelName = _.isEmpty(modelName) ? DEFAULT_BUCKET_MODEL_NAME : modelName;
+  bucketName = mongooseCommon.toCollectionName(modelName);
+  bucketName =
+    modelName === DEFAULT_BUCKET_MODEL_NAME ? DEFAULT_BUCKET_NAME : bucketName;
+
+  // create bucket
+  const options = _.merge({}, { connection, modelName, bucketName }, optns);
+  const bucket = createBucket(options);
+
+  // construct file schema
+  const schema = createFileSchema(bucket);
+
+  // apply schema plugins with model options
+  const schemaOptions = _.merge({}, schema.options);
+  _.forEach([...plugins], (plugin) => {
+    schema.plugin(plugin, schemaOptions);
+  });
+
+  // hack(to be removed): fake timestamp fields
+  schema.statics.CREATED_AT_FIELD = 'uploadDate';
+  schema.statics.UPDATED_AT_FIELD = 'uploadDate';
+
+  // compile file model
+  const fileModel = mongooseCommon.model(modelName, schema, connection);
+
+  // return model
+  return fileModel;
+}
+
+Object.defineProperty(exports, 'GridFSBucket', {
+  enumerable: true,
+  get: function () { return mongooseCommon.GridFSBucket; }
+});
+exports.DEFAULT_BUCKET_CHUNK_SIZE = DEFAULT_BUCKET_CHUNK_SIZE;
+exports.DEFAULT_BUCKET_MODEL_NAME = DEFAULT_BUCKET_MODEL_NAME;
+exports.DEFAULT_BUCKET_NAME = DEFAULT_BUCKET_NAME;
+exports.DEFAULT_BUCKET_OPTIONS = DEFAULT_BUCKET_OPTIONS;
+exports.createBucket = createBucket;
+exports.createModel = createModel;