HORIZON PROJECT

/**

 * Create a blob builder even when vendor prefixes exist

 */

var BlobBuilder = global.BlobBuilder

  || global.WebKitBlobBuilder

  || global.MSBlobBuilder

  || global.MozBlobBuilder;

/**

 * Check if Blob constructor is supported

 */

var blobSupported = (function() {

  try {

    var a = new Blob(['hi']);

    return a.size === 2;

  } catch(e) {

    return false;

  }

})();

/**

 * Check if Blob constructor supports ArrayBufferViews

 * Fails in Safari 6, so we need to map to ArrayBuffers there.

 */

var blobSupportsArrayBufferView = blobSupported && (function() {

  try {

    var b = new Blob([new Uint8Array([1,2])]);

    return b.size === 2;

  } catch(e) {

    return false;

  }

})();

/**

 * Check if BlobBuilder is supported

 */

var blobBuilderSupported = BlobBuilder

  && BlobBuilder.prototype.append

  && BlobBuilder.prototype.getBlob;

/**

 * Helper function that maps ArrayBufferViews to ArrayBuffers

 * Used by BlobBuilder constructor and old browsers that didn't

 * support it in the Blob constructor.

 */

function mapArrayBufferViews(ary) {

  for (var i = 0; i < ary.length; i++) {

    var chunk = ary[i];

    if (chunk.buffer instanceof ArrayBuffer) {

      var buf = chunk.buffer;

      // if this is a subarray, make a copy so we only

      // include the subarray region from the underlying buffer

      if (chunk.byteLength !== buf.byteLength) {

        var copy = new Uint8Array(chunk.byteLength);

        copy.set(new Uint8Array(buf, chunk.byteOffset, chunk.byteLength));

        buf = copy.buffer;

      }

      ary[i] = buf;

    }

  }

}

function BlobBuilderConstructor(ary, options) {

  options = options || {};

  var bb = new BlobBuilder();

  mapArrayBufferViews(ary);

  for (var i = 0; i < ary.length; i++) {

    bb.append(ary[i]);

  }

  return (options.type) ? bb.getBlob(options.type) : bb.getBlob();

};

function BlobConstructor(ary, options) {

  mapArrayBufferViews(ary);

  return new Blob(ary, options || {});

};

module.exports = (function() {

  if (blobSupported) {

    return blobSupportsArrayBufferView ? global.Blob : BlobConstructor;

  } else if (blobBuilderSupported) {

    return BlobBuilderConstructor;

  } else {

    return undefined;

  }

})();