// Copyright 2011 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @fileoverview Asynchronous hash computer for the Blob interface.
 *
 * The Blob interface, part of the HTML5 File API, is supported on Chrome 7+,
 * Firefox 4.0 and Opera 11. No Blob interface implementation is expected on
 * Internet Explorer 10. Chrome 11, Firefox 5.0 and the subsequent release of
 * Opera are supposed to use vendor prefixes due to evolving API, see
 * http://dev.w3.org/2006/webapi/FileAPI/ for details.
 *
 * This implementation currently uses upcoming Chrome and Firefox prefixes,
 * plus the original Blob.slice specification, as implemented on Chrome 10
 * and Firefox 4.0.
 *
 */

goog.provide('goog.crypt.BlobHasher');
goog.provide('goog.crypt.BlobHasher.EventType');

goog.require('goog.asserts');
goog.require('goog.crypt');
goog.require('goog.crypt.Hash');
goog.require('goog.debug.Logger');
goog.require('goog.events.EventTarget');
goog.require('goog.fs');



/**
 * Construct the hash computer.
 *
 * @param {!goog.crypt.Hash} hashFn The hash function to use.
 * @param {number=} opt_blockSize Processing block size.
 * @constructor
 * @extends {goog.events.EventTarget}
 */
goog.crypt.BlobHasher = function(hashFn, opt_blockSize) {
  goog.base(this);

  /**
   * The actual hash function.
   * @type {!goog.crypt.Hash}
   * @private
   */
  this.hashFn_ = hashFn;

  /**
   * The blob being processed.
   * @type {Blob}
   * @private
   */
  this.blob_ = null;

  /**
   * Computed hash value.
   * @type {Array.<number>}
   * @private
   */
  this.hashVal_ = null;

  /**
   * Number of bytes already processed.
   * @type {number}
   * @private
   */
  this.bytesProcessed_ = 0;

  /**
   * Processing block size.
   * @type {number}
   * @private
   */
  this.blockSize_ = opt_blockSize || 5000000;

  /**
   * File reader object.
   * @type {FileReader}
   * @private
   */
  this.fileReader_ = null;

  /**
   * The logger used by this object.
   * @type {!goog.debug.Logger}
   * @private
   */
  this.logger_ = goog.debug.Logger.getLogger('goog.crypt.BlobHasher');
};
goog.inherits(goog.crypt.BlobHasher, goog.events.EventTarget);


/**
 * Event names for hash computation events
 * @enum {string}
 */
goog.crypt.BlobHasher.EventType = {
  STARTED: 'started',
  PROGRESS: 'progress',
  COMPLETE: 'complete',
  ABORT: 'abort',
  ERROR: 'error'
};


/**
 * Start the hash computation.
 * @param {!Blob} blob The blob of data to compute the hash for.
 */
goog.crypt.BlobHasher.prototype.hash = function(blob) {
  this.abort();
  this.hashFn_.reset();
  this.blob_ = blob;
  this.hashVal_ = null;
  this.bytesProcessed_ = 0;
  this.dispatchEvent(goog.crypt.BlobHasher.EventType.STARTED);

  this.processNextBlock_();
};


/**
 * Abort hash computation.
 */
goog.crypt.BlobHasher.prototype.abort = function() {
  if (this.fileReader_ &&
      this.fileReader_.readyState != this.fileReader_.DONE) {
    this.fileReader_.abort();
  }
};


/**
 * @return {number} Number of bytes processed so far.
 */
goog.crypt.BlobHasher.prototype.getBytesProcessed = function() {
  return this.bytesProcessed_;
};


/**
 * @return {Array.<number>} The computed hash value or null if not ready.
 */
goog.crypt.BlobHasher.prototype.getHash = function() {
  return this.hashVal_;
};


/**
 * Helper function setting up the processing for the next block, or finalizing
 * the computation if all blocks were processed.
 * @private
 */
goog.crypt.BlobHasher.prototype.processNextBlock_ = function() {
  goog.asserts.assert(this.blob_, 'The blob has disappeared during processing');
  if (this.bytesProcessed_ < this.blob_.size) {
    // We have to reset the FileReader every time, otherwise it fails on
    // Chrome, including the latest Chrome 12 beta.
    // http://code.google.com/p/chromium/issues/detail?id=82346
    this.fileReader_ = new FileReader();
    this.fileReader_.onload = goog.bind(this.onLoad_, this);
    this.fileReader_.onabort = goog.bind(this.dispatchEvent, this,
                                         goog.crypt.BlobHasher.EventType.ABORT);
    this.fileReader_.onerror = goog.bind(this.dispatchEvent, this,
                                         goog.crypt.BlobHasher.EventType.ERROR);

    var size = Math.min(this.blob_.size - this.bytesProcessed_,
                        this.blockSize_);
    var chunk = goog.fs.sliceBlob(this.blob_, this.bytesProcessed_,
                                  this.bytesProcessed_ + size);
    if (!chunk || chunk.size != size) {
      this.logger_.severe('Failed slicing the blob');
      this.dispatchEvent(goog.crypt.BlobHasher.EventType.ERROR);
      return;
    }

    if (this.fileReader_.readAsArrayBuffer) {
      this.fileReader_.readAsArrayBuffer(chunk);
    } else if (this.fileReader_.readAsBinaryString) {
      this.fileReader_.readAsBinaryString(chunk);
    } else {
      this.logger_.severe('Failed calling the chunk reader');
      this.dispatchEvent(goog.crypt.BlobHasher.EventType.ERROR);
    }
  } else {
    this.hashVal_ = this.hashFn_.digest();
    this.dispatchEvent(goog.crypt.BlobHasher.EventType.COMPLETE);
  }
};


/**
 * Handle processing block loaded.
 * @private
 */
goog.crypt.BlobHasher.prototype.onLoad_ = function() {
  this.logger_.info('Successfully loaded a chunk');

  var array = null;
  if (this.fileReader_.result instanceof Array ||
      goog.isString(this.fileReader_.result)) {
    array = this.fileReader_.result;
  } else if (goog.global['ArrayBuffer'] && goog.global['Uint8Array'] &&
             this.fileReader_.result instanceof ArrayBuffer) {
    array = new Uint8Array(this.fileReader_.result);
  }
  if (!array) {
    this.logger_.severe('Failed reading the chunk');
    this.dispatchEvent(goog.crypt.BlobHasher.EventType.ERROR);
    return;
  }
  this.hashFn_.update(array);
  this.bytesProcessed_ += array.length;
  this.dispatchEvent(goog.crypt.BlobHasher.EventType.PROGRESS);

  this.processNextBlock_();
};