'use strict';

var utils = require('./utils');
/* jshint -W079 */
var Blob = require('blob');
var Promise = utils.Promise;

//
// PRIVATE
//

// From http://stackoverflow.com/questions/14967647/ (continues on next line)
// encode-decode-image-with-base64-breaks-image (2013-04-21)
function binaryStringToArrayBuffer(binary) {
  var length = binary.length;
  var buf = new ArrayBuffer(length);
  var arr = new Uint8Array(buf);
  var i = -1;
  while (++i < length) {
    arr[i] = binary.charCodeAt(i);
  }
  return buf;
}

// Can't find original post, but this is close
// http://stackoverflow.com/questions/6965107/ (continues on next line)
// converting-between-strings-and-arraybuffers
function arrayBufferToBinaryString(buffer) {
  var binary = '';
  var bytes = new Uint8Array(buffer);
  var length = bytes.byteLength;
  var i = -1;
  while (++i < length) {
    binary += String.fromCharCode(bytes[i]);
  }
  return binary;
}

// doesn't download the image more than once, because
// browsers aren't dumb. uses the cache
function loadImage(src, crossOrigin) {
  return new Promise(function (resolve, reject) {
    var img = new Image();
    if (crossOrigin) {
      img.crossOrigin = crossOrigin;
    }
    img.onload = function () {
      resolve(img);
    };
    img.onerror = reject;
    img.src = src;
  });
}

function imgToCanvas(img) {
  var canvas = document.createElement('canvas');

  canvas.width = img.width;
  canvas.height = img.height;

  // copy the image contents to the canvas
  var context = canvas.getContext('2d');
  context.drawImage(
    img,
    0, 0,
    img.width, img.height,
    0, 0,
    img.width, img.height);

  return canvas;
}

//
// PUBLIC
//

/**
 * Shim for
 * [new Blob()]{@link https://developer.mozilla.org/en-US/docs/Web/API/Blob.Blob}
 * to support
 * [older browsers that use the deprecated <code>BlobBuilder</code> API]{@link http://caniuse.com/blob}.
 *
 * @param {Array} parts - content of the <code>Blob</code>
 * @param {Object} options - usually just <code>{type: myContentType}</code>
 * @returns {Blob}
 */
function createBlob(parts, options) {
  options = options || {};
  if (typeof options === 'string') {
    options = {type: options}; // do you a solid here
  }
  return new Blob(parts, options);
}

/**
 * Shim for
 * [URL.createObjectURL()]{@link https://developer.mozilla.org/en-US/docs/Web/API/URL.createObjectURL}
 * to support browsers that only have the prefixed
 * <code>webkitURL</code> (e.g. Android <4.4).
 * @param {Blob} blob
 * @returns {string} url
 */
function createObjectURL(blob) {
  return (window.URL || window.webkitURL).createObjectURL(blob);
}

/**
 * Shim for
 * [URL.revokeObjectURL()]{@link https://developer.mozilla.org/en-US/docs/Web/API/URL.revokeObjectURL}
 * to support browsers that only have the prefixed
 * <code>webkitURL</code> (e.g. Android <4.4).
 * @param {string} url
 */
function revokeObjectURL(url) {
  return (window.URL || window.webkitURL).revokeObjectURL(url);
}

/**
 * Convert a <code>Blob</code> to a binary string. Returns a Promise.
 *
 * @param {Blob} blob
 * @returns {Promise} Promise that resolves with the binary string
 */
function blobToBinaryString(blob) {
  return new Promise(function (resolve, reject) {
    var reader = new FileReader();
    var hasBinaryString = typeof reader.readAsBinaryString === 'function';
    reader.onloadend = function (e) {
      var result = e.target.result || '';
      if (hasBinaryString) {
        return resolve(result);
      }
      resolve(arrayBufferToBinaryString(result));
    };
    reader.onerror = reject;
    if (hasBinaryString) {
      reader.readAsBinaryString(blob);
    } else {
      reader.readAsArrayBuffer(blob);
    }
  });
}

/**
 * Convert a base64-encoded string to a <code>Blob</code>. Returns a Promise.
 * @param {string} base64
 * @param {string|undefined} type - the content type (optional)
 * @returns {Promise} Promise that resolves with the <code>Blob</code>
 */
function base64StringToBlob(base64, type) {
  return Promise.resolve().then(function () {
    var parts = [binaryStringToArrayBuffer(atob(base64))];
    return type ? createBlob(parts, {type: type}) : createBlob(parts);
  });
}

/**
 * Convert a binary string to a <code>Blob</code>. Returns a Promise.
 * @param {string} binary
 * @param {string|undefined} type - the content type (optional)
 * @returns {Promise} Promise that resolves with the <code>Blob</code>
 */
function binaryStringToBlob(binary, type) {
  return Promise.resolve().then(function () {
    return base64StringToBlob(btoa(binary), type);
  });
}

/**
 * Convert a <code>Blob</code> to a binary string. Returns a Promise.
 * @param {Blob} blob
 * @returns {Promise} Promise that resolves with the binary string
 */
function blobToBase64String(blob) {
  return blobToBinaryString(blob).then(function (binary) {
    return btoa(binary);
  });
}

/**
 * Convert a data URL string
 * (e.g. <code>'data:image/png;base64,iVBORw0KG...'</code>)
 * to a <code>Blob</code>. Returns a Promise.
 * @param {string} dataURL
 * @returns {Promise} Promise that resolves with the <code>Blob</code>
 */
function dataURLToBlob(dataURL) {
  return Promise.resolve().then(function () {
    var type = dataURL.match(/data:([^;]+)/)[1];
    var base64 = dataURL.replace(/^[^,]+,/, '');

    var buff = binaryStringToArrayBuffer(atob(base64));
    return createBlob([buff], {type: type});
  });
}

/**
 * Convert an image's <code>src</code> URL to a data URL by loading the image and painting
 * it to a <code>canvas</code>. Returns a Promise.
 *
 * <p/>Note: this will coerce the image to the desired content type, and it
 * will only paint the first frame of an animated GIF.
 *
 * @param {string} src
 * @param {string|undefined} type - the content type (optional, defaults to 'image/png')
 * @param {string|undefined} crossOrigin - for CORS-enabled images, set this to
 *                                         'Anonymous' to avoid "tainted canvas" errors
 * @returns {Promise} Promise that resolves with the data URL string
 */
function imgSrcToDataURL(src, type, crossOrigin) {
  type = type || 'image/png';

  return loadImage(src, crossOrigin).then(function (img) {
    return imgToCanvas(img);
  }).then(function (canvas) {
    return canvas.toDataURL(type);
  });
}

/**
 * Convert a <code>canvas</code> to a <code>Blob</code>. Returns a Promise.
 * @param {string} canvas
 * @param {string|undefined} type - the content type (optional, defaults to 'image/png')
 * @returns {Promise} Promise that resolves with the <code>Blob</code>
 */
function canvasToBlob(canvas, type) {
  return Promise.resolve().then(function () {
    if (typeof canvas.toBlob === 'function') {
      return new Promise(function (resolve) {
        canvas.toBlob(resolve, type);
      });
    }
    return dataURLToBlob(canvas.toDataURL(type));
  });
}

/**
 * Convert an image's <code>src</code> URL to a <code>Blob</code> by loading the image and painting
 * it to a <code>canvas</code>. Returns a Promise.
 *
 * <p/>Note: this will coerce the image to the desired content type, and it
 * will only paint the first frame of an animated GIF.
 *
 * @param {string} src
 * @param {string|undefined} type - the content type (optional, defaults to 'image/png')
 * @param {string|undefined} crossOrigin - for CORS-enabled images, set this to
 *                                         'Anonymous' to avoid "tainted canvas" errors
 * @returns {Promise} Promise that resolves with the <code>Blob</code>
 */
function imgSrcToBlob(src, type, crossOrigin) {
  type = type || 'image/png';

  return loadImage(src, crossOrigin).then(function (img) {
    return imgToCanvas(img);
  }).then(function (canvas) {
    return canvasToBlob(canvas, type);
  });
}

/**
 * Convert an <code>ArrayBuffer</code> to a <code>Blob</code>. Returns a Promise.
 *
 * @param {ArrayBuffer} buffer
 * @param {string|undefined} type - the content type (optional)
 * @returns {Promise} Promise that resolves with the <code>Blob</code>
 */
function arrayBufferToBlob(buffer, type) {
  return Promise.resolve().then(function () {
    return createBlob([buffer], type);
  });
}

/**
 * Convert a <code>Blob</code> to an <code>ArrayBuffer</code>. Returns a Promise.
 * @param {Blob} blob
 * @returns {Promise} Promise that resolves with the <code>ArrayBuffer</code>
 */
function blobToArrayBuffer(blob) {
  return blobToBinaryString(blob).then(function (binary) {
    return binaryStringToArrayBuffer(binary);
  });
}

module.exports = {
  createBlob         : createBlob,
  createObjectURL    : createObjectURL,
  revokeObjectURL    : revokeObjectURL,
  imgSrcToBlob       : imgSrcToBlob,
  imgSrcToDataURL    : imgSrcToDataURL,
  canvasToBlob       : canvasToBlob,
  dataURLToBlob      : dataURLToBlob,
  blobToBase64String : blobToBase64String,
  base64StringToBlob : base64StringToBlob,
  binaryStringToBlob : binaryStringToBlob,
  blobToBinaryString : blobToBinaryString,
  arrayBufferToBlob  : arrayBufferToBlob,
  blobToArrayBuffer  : blobToArrayBuffer
};