// [qr.js](http://neocotic.com/qr.js)  
// (c) 2014 Alasdair Mercer  
// Licensed under the GPL Version 3 license.  
// Based on [jsqrencode](http://code.google.com/p/jsqrencode/)  
// (c) 2010 tz@execpc.com  
// Licensed under the GPL Version 3 license.  
// For all details and documentation:  
// <http://neocotic.com/qr.js>

(function (root) {

  'use strict';

  // Private constants
  // -----------------

  // Alignment pattern.
  var ALIGNMENT_DELTA = [
    0,  11, 15, 19, 23, 27, 31,
    16, 18, 20, 22, 24, 26, 28, 20, 22, 24, 24, 26, 28, 28, 22, 24, 24,
    26, 26, 28, 28, 24, 24, 26, 26, 26, 28, 28, 24, 26, 26, 26, 28, 28
  ];
  // Default MIME type.
  var DEFAULT_MIME = 'image/png';
  // MIME used to initiate a browser download prompt when `qr.save` is called.
  var DOWNLOAD_MIME = 'image/octet-stream';
  // There are four elements per version. The first two indicate the number of blocks, then the
  // data width, and finally the ECC width.
  var ECC_BLOCKS = [
    1,  0,  19,  7,     1,  0,  16,  10,    1,  0,  13,  13,    1,  0,  9,   17,
    1,  0,  34,  10,    1,  0,  28,  16,    1,  0,  22,  22,    1,  0,  16,  28,
    1,  0,  55,  15,    1,  0,  44,  26,    2,  0,  17,  18,    2,  0,  13,  22,
    1,  0,  80,  20,    2,  0,  32,  18,    2,  0,  24,  26,    4,  0,  9,   16,
    1,  0,  108, 26,    2,  0,  43,  24,    2,  2,  15,  18,    2,  2,  11,  22,
    2,  0,  68,  18,    4,  0,  27,  16,    4,  0,  19,  24,    4,  0,  15,  28,
    2,  0,  78,  20,    4,  0,  31,  18,    2,  4,  14,  18,    4,  1,  13,  26,
    2,  0,  97,  24,    2,  2,  38,  22,    4,  2,  18,  22,    4,  2,  14,  26,
    2,  0,  116, 30,    3,  2,  36,  22,    4,  4,  16,  20,    4,  4,  12,  24,
    2,  2,  68,  18,    4,  1,  43,  26,    6,  2,  19,  24,    6,  2,  15,  28,
    4,  0,  81,  20,    1,  4,  50,  30,    4,  4,  22,  28,    3,  8,  12,  24,
    2,  2,  92,  24,    6,  2,  36,  22,    4,  6,  20,  26,    7,  4,  14,  28,
    4,  0,  107, 26,    8,  1,  37,  22,    8,  4,  20,  24,    12, 4,  11,  22,
    3,  1,  115, 30,    4,  5,  40,  24,    11, 5,  16,  20,    11, 5,  12,  24,
    5,  1,  87,  22,    5,  5,  41,  24,    5,  7,  24,  30,    11, 7,  12,  24,
    5,  1,  98,  24,    7,  3,  45,  28,    15, 2,  19,  24,    3,  13, 15,  30,
    1,  5,  107, 28,    10, 1,  46,  28,    1,  15, 22,  28,    2,  17, 14,  28,
    5,  1,  120, 30,    9,  4,  43,  26,    17, 1,  22,  28,    2,  19, 14,  28,
    3,  4,  113, 28,    3,  11, 44,  26,    17, 4,  21,  26,    9,  16, 13,  26,
    3,  5,  107, 28,    3,  13, 41,  26,    15, 5,  24,  30,    15, 10, 15,  28,
    4,  4,  116, 28,    17, 0,  42,  26,    17, 6,  22,  28,    19, 6,  16,  30,
    2,  7,  111, 28,    17, 0,  46,  28,    7,  16, 24,  30,    34, 0,  13,  24,
    4,  5,  121, 30,    4,  14, 47,  28,    11, 14, 24,  30,    16, 14, 15,  30,
    6,  4,  117, 30,    6,  14, 45,  28,    11, 16, 24,  30,    30, 2,  16,  30,
    8,  4,  106, 26,    8,  13, 47,  28,    7,  22, 24,  30,    22, 13, 15,  30,
    10, 2,  114, 28,    19, 4,  46,  28,    28, 6,  22,  28,    33, 4,  16,  30,
    8,  4,  122, 30,    22, 3,  45,  28,    8,  26, 23,  30,    12, 28, 15,  30,
    3,  10, 117, 30,    3,  23, 45,  28,    4,  31, 24,  30,    11, 31, 15,  30,
    7,  7,  116, 30,    21, 7,  45,  28,    1,  37, 23,  30,    19, 26, 15,  30,
    5,  10, 115, 30,    19, 10, 47,  28,    15, 25, 24,  30,    23, 25, 15,  30,
    13, 3,  115, 30,    2,  29, 46,  28,    42, 1,  24,  30,    23, 28, 15,  30,
    17, 0,  115, 30,    10, 23, 46,  28,    10, 35, 24,  30,    19, 35, 15,  30,
    17, 1,  115, 30,    14, 21, 46,  28,    29, 19, 24,  30,    11, 46, 15,  30,
    13, 6,  115, 30,    14, 23, 46,  28,    44, 7,  24,  30,    59, 1,  16,  30,
    12, 7,  121, 30,    12, 26, 47,  28,    39, 14, 24,  30,    22, 41, 15,  30,
    6,  14, 121, 30,    6,  34, 47,  28,    46, 10, 24,  30,    2,  64, 15,  30,
    17, 4,  122, 30,    29, 14, 46,  28,    49, 10, 24,  30,    24, 46, 15,  30,
    4,  18, 122, 30,    13, 32, 46,  28,    48, 14, 24,  30,    42, 32, 15,  30,
    20, 4,  117, 30,    40, 7,  47,  28,    43, 22, 24,  30,    10, 67, 15,  30,
    19, 6,  118, 30,    18, 31, 47,  28,    34, 34, 24,  30,    20, 61, 15,  30
  ];
  // Map of human-readable ECC levels.
  var ECC_LEVELS = {
    L: 1,
    M: 2,
    Q: 3,
    H: 4
  };
  // Final format bits with mask (level << 3 | mask).
  var FINAL_FORMAT = [
    0x77c4, 0x72f3, 0x7daa, 0x789d, 0x662f, 0x6318, 0x6c41, 0x6976, /* L */
    0x5412, 0x5125, 0x5e7c, 0x5b4b, 0x45f9, 0x40ce, 0x4f97, 0x4aa0, /* M */
    0x355f, 0x3068, 0x3f31, 0x3a06, 0x24b4, 0x2183, 0x2eda, 0x2bed, /* Q */
    0x1689, 0x13be, 0x1ce7, 0x19d0, 0x0762, 0x0255, 0x0d0c, 0x083b  /* H */
  ];
  // Galois field exponent table.
  var GALOIS_EXPONENT = [
    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1d, 0x3a, 0x74, 0xe8, 0xcd, 0x87, 0x13, 0x26,
    0x4c, 0x98, 0x2d, 0x5a, 0xb4, 0x75, 0xea, 0xc9, 0x8f, 0x03, 0x06, 0x0c, 0x18, 0x30, 0x60, 0xc0,
    0x9d, 0x27, 0x4e, 0x9c, 0x25, 0x4a, 0x94, 0x35, 0x6a, 0xd4, 0xb5, 0x77, 0xee, 0xc1, 0x9f, 0x23,
    0x46, 0x8c, 0x05, 0x0a, 0x14, 0x28, 0x50, 0xa0, 0x5d, 0xba, 0x69, 0xd2, 0xb9, 0x6f, 0xde, 0xa1,
    0x5f, 0xbe, 0x61, 0xc2, 0x99, 0x2f, 0x5e, 0xbc, 0x65, 0xca, 0x89, 0x0f, 0x1e, 0x3c, 0x78, 0xf0,
    0xfd, 0xe7, 0xd3, 0xbb, 0x6b, 0xd6, 0xb1, 0x7f, 0xfe, 0xe1, 0xdf, 0xa3, 0x5b, 0xb6, 0x71, 0xe2,
    0xd9, 0xaf, 0x43, 0x86, 0x11, 0x22, 0x44, 0x88, 0x0d, 0x1a, 0x34, 0x68, 0xd0, 0xbd, 0x67, 0xce,
    0x81, 0x1f, 0x3e, 0x7c, 0xf8, 0xed, 0xc7, 0x93, 0x3b, 0x76, 0xec, 0xc5, 0x97, 0x33, 0x66, 0xcc,
    0x85, 0x17, 0x2e, 0x5c, 0xb8, 0x6d, 0xda, 0xa9, 0x4f, 0x9e, 0x21, 0x42, 0x84, 0x15, 0x2a, 0x54,
    0xa8, 0x4d, 0x9a, 0x29, 0x52, 0xa4, 0x55, 0xaa, 0x49, 0x92, 0x39, 0x72, 0xe4, 0xd5, 0xb7, 0x73,
    0xe6, 0xd1, 0xbf, 0x63, 0xc6, 0x91, 0x3f, 0x7e, 0xfc, 0xe5, 0xd7, 0xb3, 0x7b, 0xf6, 0xf1, 0xff,
    0xe3, 0xdb, 0xab, 0x4b, 0x96, 0x31, 0x62, 0xc4, 0x95, 0x37, 0x6e, 0xdc, 0xa5, 0x57, 0xae, 0x41,
    0x82, 0x19, 0x32, 0x64, 0xc8, 0x8d, 0x07, 0x0e, 0x1c, 0x38, 0x70, 0xe0, 0xdd, 0xa7, 0x53, 0xa6,
    0x51, 0xa2, 0x59, 0xb2, 0x79, 0xf2, 0xf9, 0xef, 0xc3, 0x9b, 0x2b, 0x56, 0xac, 0x45, 0x8a, 0x09,
    0x12, 0x24, 0x48, 0x90, 0x3d, 0x7a, 0xf4, 0xf5, 0xf7, 0xf3, 0xfb, 0xeb, 0xcb, 0x8b, 0x0b, 0x16,
    0x2c, 0x58, 0xb0, 0x7d, 0xfa, 0xe9, 0xcf, 0x83, 0x1b, 0x36, 0x6c, 0xd8, 0xad, 0x47, 0x8e, 0x00
  ];
  // Galois field log table.
  var GALOIS_LOG = [
    0xff, 0x00, 0x01, 0x19, 0x02, 0x32, 0x1a, 0xc6, 0x03, 0xdf, 0x33, 0xee, 0x1b, 0x68, 0xc7, 0x4b,
    0x04, 0x64, 0xe0, 0x0e, 0x34, 0x8d, 0xef, 0x81, 0x1c, 0xc1, 0x69, 0xf8, 0xc8, 0x08, 0x4c, 0x71,
    0x05, 0x8a, 0x65, 0x2f, 0xe1, 0x24, 0x0f, 0x21, 0x35, 0x93, 0x8e, 0xda, 0xf0, 0x12, 0x82, 0x45,
    0x1d, 0xb5, 0xc2, 0x7d, 0x6a, 0x27, 0xf9, 0xb9, 0xc9, 0x9a, 0x09, 0x78, 0x4d, 0xe4, 0x72, 0xa6,
    0x06, 0xbf, 0x8b, 0x62, 0x66, 0xdd, 0x30, 0xfd, 0xe2, 0x98, 0x25, 0xb3, 0x10, 0x91, 0x22, 0x88,
    0x36, 0xd0, 0x94, 0xce, 0x8f, 0x96, 0xdb, 0xbd, 0xf1, 0xd2, 0x13, 0x5c, 0x83, 0x38, 0x46, 0x40,
    0x1e, 0x42, 0xb6, 0xa3, 0xc3, 0x48, 0x7e, 0x6e, 0x6b, 0x3a, 0x28, 0x54, 0xfa, 0x85, 0xba, 0x3d,
    0xca, 0x5e, 0x9b, 0x9f, 0x0a, 0x15, 0x79, 0x2b, 0x4e, 0xd4, 0xe5, 0xac, 0x73, 0xf3, 0xa7, 0x57,
    0x07, 0x70, 0xc0, 0xf7, 0x8c, 0x80, 0x63, 0x0d, 0x67, 0x4a, 0xde, 0xed, 0x31, 0xc5, 0xfe, 0x18,
    0xe3, 0xa5, 0x99, 0x77, 0x26, 0xb8, 0xb4, 0x7c, 0x11, 0x44, 0x92, 0xd9, 0x23, 0x20, 0x89, 0x2e,
    0x37, 0x3f, 0xd1, 0x5b, 0x95, 0xbc, 0xcf, 0xcd, 0x90, 0x87, 0x97, 0xb2, 0xdc, 0xfc, 0xbe, 0x61,
    0xf2, 0x56, 0xd3, 0xab, 0x14, 0x2a, 0x5d, 0x9e, 0x84, 0x3c, 0x39, 0x53, 0x47, 0x6d, 0x41, 0xa2,
    0x1f, 0x2d, 0x43, 0xd8, 0xb7, 0x7b, 0xa4, 0x76, 0xc4, 0x17, 0x49, 0xec, 0x7f, 0x0c, 0x6f, 0xf6,
    0x6c, 0xa1, 0x3b, 0x52, 0x29, 0x9d, 0x55, 0xaa, 0xfb, 0x60, 0x86, 0xb1, 0xbb, 0xcc, 0x3e, 0x5a,
    0xcb, 0x59, 0x5f, 0xb0, 0x9c, 0xa9, 0xa0, 0x51, 0x0b, 0xf5, 0x16, 0xeb, 0x7a, 0x75, 0x2c, 0xd7,
    0x4f, 0xae, 0xd5, 0xe9, 0xe6, 0xe7, 0xad, 0xe8, 0x74, 0xd6, 0xf4, 0xea, 0xa8, 0x50, 0x58, 0xaf
  ];
  // *Badness* coefficients.
  var N1 = 3;
  var N2 = 3;
  var N3 = 40;
  var N4 = 10;
  // Version pattern.
  var VERSION_BLOCK = [ 
    0xc94, 0x5bc, 0xa99, 0x4d3, 0xbf6, 0x762, 0x847, 0x60d, 0x928, 0xb78, 0x45d, 0xa17, 0x532,
    0x9a6, 0x683, 0x8c9, 0x7ec, 0xec4, 0x1e1, 0xfab, 0x08e, 0xc1a, 0x33f, 0xd75, 0x250, 0x9d5,
    0x6f0, 0x8ba, 0x79f, 0xb0b, 0x42e, 0xa64, 0x541, 0xc69
  ];
  // Mode for node.js file system file writes.
  var WRITE_MODE = parseInt('0666', 8);

  // Private variables
  // -----------------

  // Run lengths for badness.
  var badBuffer = [];
  // Constructor for `canvas` elements in the node.js environment.
  var Canvas;
  // Data block.
  var dataBlock;
  // ECC data blocks and tables.
  var eccBlock, neccBlock1, neccBlock2;
  // ECC buffer.
  var eccBuffer = [];
  // ECC level (defaults to **L**).
  var eccLevel = 1;
  // Image buffer.
  var frameBuffer = [];
  // Fixed part of the image.
  var frameMask = [];
  // File system within the node.js environment.
  var fs;
  // Constructor for `img` elements in the node.js environment.
  var Image;
  // Indicates whether or not this script is running in node.js.
  var inNode = false;
  // Generator polynomial.
  var polynomial = [];
  // Save the previous value of the `qr` variable.
  var previousQr = root.qr;
  // Data input buffer.
  var stringBuffer = [];
  // Version for the data.
  var version;
  // Data width is based on `version`.
  var width;

  // Private functions
  // -----------------

  // Create a new canvas  using `document.createElement` unless script is running in node.js, in
  // which case the `canvas` module is used.
  function createCanvas() {
    return inNode ? new Canvas() : root.document.createElement('canvas');
  }

  // Create a new image using `document.createElement` unless script is running in node.js, in
  // which case the `canvas` module is used.
  function createImage() {
    return inNode ? new Image() : root.document.createElement('img');
  }

  // Force the canvas image to be downloaded in the browser.  
  // Optionally, a `callback` function can be specified which will be called upon completed. Since
  // this is not an asynchronous operation, this is merely convenient and helps simplify the
  // calling code.
  function download(cvs, data, callback) {
    var mime = data.mime || DEFAULT_MIME;

    root.location.href = cvs.toDataURL(mime).replace(mime, DOWNLOAD_MIME);

    if (typeof callback === 'function') callback();
  }

  // Normalize the `data` that is provided to the main API.
  function normalizeData(data) {
    if (typeof data === 'string') data = { value: data };
    return data || {};
  }

  // Override the `qr` API methods that require HTML5 canvas support to throw a relevant error.
  function overrideAPI(qr) {
    var methods = [ 'canvas', 'image', 'save', 'saveSync', 'toDataURL' ];
    var i;

    function overrideMethod(name) {
      qr[name] = function () {
        throw new Error(name + ' requires HTML5 canvas element support');
      };
    }

    for (i = 0; i < methods.length; i++) {
      overrideMethod(methods[i]);
    }
  }

  // Asynchronously write the data of the rendered canvas to a given file path.
  function writeFile(cvs, data, callback) {
    if (typeof data.path !== 'string') {
      return callback(new TypeError('Invalid path type: ' + typeof data.path));
    }

    var fd, buff;

    // Write the buffer to the open file stream once both prerequisites are met.
    function writeBuffer() {
      fs.write(fd, buff, 0, buff.length, 0, function (error) {
        fs.close(fd);

        callback(error);
      });
    }

    // Create a buffer of the canvas' data.
    cvs.toBuffer(function (error, _buff) {
      if (error) return callback(error);

      buff = _buff;
      if (fd) {
        writeBuffer();
      }
    });

    // Open a stream for the file to be written.
    fs.open(data.path, 'w', WRITE_MODE, function (error, _fd) {
      if (error) return callback(error);

      fd = _fd;
      if (buff) {
        writeBuffer();
      }
    });
  }

  // Write the data of the rendered canvas to a given file path.
  function writeFileSync(cvs, data) {
    if (typeof data.path !== 'string') {
      throw new TypeError('Invalid path type: ' + typeof data.path);
    }

    var buff = cvs.toBuffer();
    var fd = fs.openSync(data.path, 'w', WRITE_MODE);

    try {
      fs.writeSync(fd, buff, 0, buff.length, 0);
    } finally {
      fs.closeSync(fd);
    }
  }

  // Set bit to indicate cell in frame is immutable (symmetric around diagonal).
  function setMask(x, y) {
    var bit;

    if (x > y) {
      bit = x;
      x   = y;
      y   = bit;
    }

    bit   = y;
    bit  *= y;
    bit  += y;
    bit >>= 1;
    bit  += x;

    frameMask[bit] = 1;
  }

  // Enter alignment pattern. Foreground colour to frame, background to mask. Frame will be merged
  // with mask later.
  function addAlignment(x, y) {
    var i;

    frameBuffer[x + width * y] = 1;

    for (i = -2; i < 2; i++) {
      frameBuffer[(x + i)     + width * (y - 2)]     = 1;
      frameBuffer[(x - 2)     + width * (y + i + 1)] = 1;
      frameBuffer[(x + 2)     + width * (y + i)]     = 1;
      frameBuffer[(x + i + 1) + width * (y + 2)]     = 1;
    }

    for (i = 0; i < 2; i++) {
      setMask(x - 1, y + i);
      setMask(x + 1, y - i);
      setMask(x - i, y - 1);
      setMask(x + i, y + 1);
    }
  }

  // Exponentiation mod N.
  function modN(x) {
    while (x >= 255) {
      x -= 255;
      x  = (x >> 8) + (x & 255);
    }

    return x;
  }

  // Calculate and append `ecc` data to the `data` block. If block is in the string buffer the
  // indices to buffers are used.
  function appendData(data, dataLength, ecc, eccLength) {
    var bit, i, j;

    for (i = 0; i < eccLength; i++) {
      stringBuffer[ecc + i] = 0;
    }

    for (i = 0; i < dataLength; i++) {
      bit = GALOIS_LOG[stringBuffer[data + i] ^ stringBuffer[ecc]];

      if (bit !== 255) {
        for (j = 1; j < eccLength; j++) {
          stringBuffer[ecc + j - 1] = stringBuffer[ecc + j] ^
              GALOIS_EXPONENT[modN(bit + polynomial[eccLength - j])];
        }
      } else {
        for (j = ecc; j < ecc + eccLength; j++) {
          stringBuffer[j] = stringBuffer[j + 1];
        }
      }

      stringBuffer[ecc + eccLength - 1] = bit === 255 ? 0 :
          GALOIS_EXPONENT[modN(bit + polynomial[0])];
    }
  }

  // Check mask since symmetricals use half.
  function isMasked(x, y) {
    var bit;

    if (x > y) {
      bit = x;
      x   = y;
      y   = bit;
    }

    bit   = y;
    bit  += y * y;
    bit >>= 1;
    bit  += x;

    return frameMask[bit] === 1;
  }

  // Apply the selected mask out of the 8 options.
  function applyMask(mask) {
    var x, y, r3x, r3y;

    switch (mask) {
      case 0:
        for (y = 0; y < width; y++) {
          for (x = 0; x < width; x++) {
            if (!((x + y) & 1) && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 1:
        for (y = 0; y < width; y++) {
          for (x = 0; x < width; x++) {
            if (!(y & 1) && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 2:
        for (y = 0; y < width; y++) {
          for (r3x = 0, x = 0; x < width; x++, r3x++) {
            if (r3x === 3) r3x = 0;

            if (!r3x && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 3:
        for (r3y = 0, y = 0; y < width; y++, r3y++) {
          if (r3y === 3) r3y = 0;

          for (r3x = r3y, x = 0; x < width; x++, r3x++) {
            if (r3x === 3) r3x = 0;

            if (!r3x && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 4:
        for (y = 0; y < width; y++) {
          for (r3x = 0, r3y = ((y >> 1) & 1), x = 0; x < width; x++, r3x++) {
            if (r3x === 3) {
              r3x = 0;
              r3y = !r3y;
            }

            if (!r3y && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 5:
        for (r3y = 0, y = 0; y < width; y++, r3y++) {
          if (r3y === 3) r3y = 0;

          for (r3x = 0, x = 0; x < width; x++, r3x++) {
            if (r3x === 3) r3x = 0;

            if (!((x & y & 1) + !(!r3x | !r3y)) && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 6:
        for (r3y = 0, y = 0; y < width; y++, r3y++) {
          if (r3y === 3) r3y = 0;

          for (r3x = 0, x = 0; x < width; x++, r3x++) {
            if (r3x === 3) r3x = 0;

            if (!(((x & y & 1) + (r3x && (r3x === r3y))) & 1) && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
      case 7:
        for (r3y = 0, y = 0; y < width; y++, r3y++) {
          if (r3y === 3) r3y = 0;

          for (r3x = 0, x = 0; x < width; x++, r3x++) {
            if (r3x === 3) r3x = 0;

            if (!(((r3x && (r3x === r3y)) + ((x + y) & 1)) & 1) && !isMasked(x, y)) {
              frameBuffer[x + y * width] ^= 1;
            }
          }
        }

        break;
    }
  }

  // Using the table for the length of each run, calculate the amount of bad image. Long runs or
  // those that look like finders are called twice; once for X and Y.
  function getBadRuns(length) {
    var badRuns = 0;
    var i;

    for (i = 0; i <= length; i++) {
      if (badBuffer[i] >= 5) {
        badRuns += N1 + badBuffer[i] - 5;
      }
    }

    // FBFFFBF as in finder.
    for (i = 3; i < length - 1; i += 2) {
      if (badBuffer[i - 2] === badBuffer[i + 2] &&
          badBuffer[i + 2] === badBuffer[i - 1] &&
          badBuffer[i - 1] === badBuffer[i + 1] &&
          badBuffer[i - 1] * 3 === badBuffer[i] &&
          // Background around the foreground pattern? Not part of the specs.
          (badBuffer[i - 3] === 0 || i + 3 > length ||
           badBuffer[i - 3] * 3 >= badBuffer[i] * 4 ||
           badBuffer[i + 3] * 3 >= badBuffer[i] * 4)) {
        badRuns += N3;
      }
    }

    return badRuns;
  }

  // Calculate how bad the masked image is (e.g. blocks, imbalance, runs, or finders).
  function checkBadness() {
    var b, b1, bad, big, bw, count, h, x, y;
    bad = bw = count = 0;

    // Blocks of same colour.
    for (y = 0; y < width - 1; y++) {
      for (x = 0; x < width - 1; x++) {
            // All foreground colour.
        if ((frameBuffer[x + width * y] &&
             frameBuffer[(x + 1) + width * y] &&
             frameBuffer[x + width * (y + 1)] &&
             frameBuffer[(x + 1) + width * (y + 1)]) ||
            // All background colour.
            !(frameBuffer[x + width * y] ||
              frameBuffer[(x + 1) + width * y] ||
              frameBuffer[x + width * (y + 1)] ||
              frameBuffer[(x + 1) + width * (y + 1)])) {
          bad += N2;
        }
      }
    }

    // X runs.
    for (y = 0; y < width; y++) {
      badBuffer[0] = 0;

      for (h = b = x = 0; x < width; x++) {
        if ((b1 = frameBuffer[x + width * y]) === b) {
          badBuffer[h]++;
        } else {
          badBuffer[++h] = 1;
        }

        b   = b1;
        bw += b ? 1 : -1;
      }

      bad += getBadRuns(h);
    }

    if (bw < 0) bw = -bw;

    big   = bw;
    big  += big << 2;
    big <<= 1;

    while (big > width * width) {
      big -= width * width;
      count++;
    }

    bad += count * N4;

    // Y runs.
    for (x = 0; x < width; x++) {
      badBuffer[0] = 0;

      for (h = b = y = 0; y < width; y++) {
        if ((b1 = frameBuffer[x + width * y]) === b) {
          badBuffer[h]++;
        } else {
          badBuffer[++h] = 1;
        }

        b = b1;
      }

      bad += getBadRuns(h);
    }

    return bad;
  }

  // Generate the encoded QR image for the string provided.
  function generateFrame(str) {
    var i, j, k, m, t, v, x, y;

    // Find the smallest version that fits the string.
    t = str.length;

    version = 0;

    do {
      version++;

      k = (eccLevel - 1) * 4 + (version - 1) * 16;

      neccBlock1 = ECC_BLOCKS[k++];
      neccBlock2 = ECC_BLOCKS[k++];
      dataBlock  = ECC_BLOCKS[k++];
      eccBlock   = ECC_BLOCKS[k];

      k = dataBlock * (neccBlock1 + neccBlock2) + neccBlock2 - 3 + (version <= 9);

      if (t <= k) break;
    } while (version < 40);

    // FIXME: Ensure that it fits insted of being truncated.
    width = 17 + 4 * version;

    // Allocate, clear and setup data structures.
    v = dataBlock + (dataBlock + eccBlock) * (neccBlock1 + neccBlock2) + neccBlock2;

    for (t = 0; t < v; t++) {
      eccBuffer[t] = 0;
    }

    stringBuffer = str.slice(0);

    for (t = 0; t < width * width; t++) {
      frameBuffer[t] = 0;
    }

    for (t = 0; t < (width * (width + 1) + 1) / 2; t++) {
      frameMask[t] = 0;
    }

    // Insert finders: Foreground colour to frame and background to mask.
    for (t = 0; t < 3; t++) {
      k = y = 0;

      if (t === 1) k = (width - 7);
      if (t === 2) y = (width - 7);

      frameBuffer[(y + 3) + width * (k + 3)] = 1;

      for (x = 0; x < 6; x++) {
        frameBuffer[(y + x) + width * k] = 1;
        frameBuffer[y + width * (k + x + 1)] = 1;
        frameBuffer[(y + 6) + width * (k + x)] = 1;
        frameBuffer[(y + x + 1) + width * (k + 6)] = 1;
      }

      for (x = 1; x < 5; x++) {
        setMask(y + x, k + 1);
        setMask(y + 1, k + x + 1);
        setMask(y + 5, k + x);
        setMask(y + x + 1, k + 5);
      }

      for (x = 2; x < 4; x++) {
        frameBuffer[(y + x) + width * (k + 2)] = 1;
        frameBuffer[(y + 2) + width * (k + x + 1)] = 1;
        frameBuffer[(y + 4) + width * (k + x)] = 1;
        frameBuffer[(y + x + 1) + width * (k + 4)] = 1;
      }
    }

    // Alignment blocks.
    if (version > 1) {
      t = ALIGNMENT_DELTA[version];
      y = width - 7;

      for (;;) {
        x = width - 7;

        while (x > t - 3) {
          addAlignment(x, y);

          if (x < t) break;

          x -= t;
        }

        if (y <= t + 9) break;

        y -= t;

        addAlignment(6, y);
        addAlignment(y, 6);
      }
    }

    // Single foreground cell.
    frameBuffer[8 + width * (width - 8)] = 1;

    // Timing gap (mask only).
    for (y = 0; y < 7; y++) {
      setMask(7, y);
      setMask(width - 8, y);
      setMask(7, y + width - 7);
    }

    for (x = 0; x < 8; x++) {
      setMask(x, 7);
      setMask(x + width - 8, 7);
      setMask(x, width - 8);
    }

    // Reserve mask, format area.
    for (x = 0; x < 9; x++) {
      setMask(x, 8);
    }

    for (x = 0; x < 8; x++) {
      setMask(x + width - 8, 8);
      setMask(8, x);
    }

    for (y = 0; y < 7; y++) {
      setMask(8, y + width - 7);
    }

    // Timing row/column.
    for (x = 0; x < width - 14; x++) {
      if (x & 1) {
        setMask(8 + x, 6);
        setMask(6, 8 + x);
      } else {
        frameBuffer[(8 + x) + width * 6] = 1;
        frameBuffer[6 + width * (8 + x)] = 1;
      }
    }

    // Version block.
    if (version > 6) {
      t = VERSION_BLOCK[version - 7];
      k = 17;

      for (x = 0; x < 6; x++) {
        for (y = 0; y < 3; y++, k--) {
          if (1 & (k > 11 ? version >> (k - 12) : t >> k)) {
            frameBuffer[(5 - x) + width * (2 - y + width - 11)] = 1;
            frameBuffer[(2 - y + width - 11) + width * (5 - x)] = 1;
          } else {
            setMask(5 - x, 2 - y + width - 11);
            setMask(2 - y + width - 11, 5 - x);
          }
        }
      }
    }

    // Sync mask bits. Only set above for background cells, so now add the foreground.
    for (y = 0; y < width; y++) {
      for (x = 0; x <= y; x++) {
        if (frameBuffer[x + width * y]) {
          setMask(x, y);
        }
      }
    }

    // Convert string to bit stream. 8-bit data to QR-coded 8-bit data (numeric, alphanum, or kanji
    // not supported).
    v = stringBuffer.length;

    // String to array.
    for (i = 0; i < v; i++) {
      eccBuffer[i] = stringBuffer.charCodeAt(i);
    }

    stringBuffer = eccBuffer.slice(0);

    // Calculate max string length.
    x = dataBlock * (neccBlock1 + neccBlock2) + neccBlock2;

    if (v >= x - 2) {
      v = x - 2;

      if (version > 9) v--;
    }

    // Shift and re-pack to insert length prefix.
    i = v;

    if (version > 9) {
      stringBuffer[i + 2] = 0;
      stringBuffer[i + 3] = 0;

      while (i--) {
        t = stringBuffer[i];

        stringBuffer[i + 3] |= 255 & (t << 4);
        stringBuffer[i + 2] = t >> 4;
      }

      stringBuffer[2] |= 255 & (v << 4);
      stringBuffer[1] = v >> 4;
      stringBuffer[0] = 0x40 | (v >> 12);
    } else {
      stringBuffer[i + 1] = 0;
      stringBuffer[i + 2] = 0;

      while (i--) {
        t = stringBuffer[i];

        stringBuffer[i + 2] |= 255 & (t << 4);
        stringBuffer[i + 1] = t >> 4;
      }

      stringBuffer[1] |= 255 & (v << 4);
      stringBuffer[0] = 0x40 | (v >> 4);
    }

    // Fill to end with pad pattern.
    i = v + 3 - (version < 10);

    while (i < x) {
      stringBuffer[i++] = 0xec;
      stringBuffer[i++] = 0x11;
    }

    // Calculate generator polynomial.
    polynomial[0] = 1;

    for (i = 0; i < eccBlock; i++) {
      polynomial[i + 1] = 1;

      for (j = i; j > 0; j--) {
        polynomial[j] = polynomial[j] ? polynomial[j - 1] ^
            GALOIS_EXPONENT[modN(GALOIS_LOG[polynomial[j]] + i)] : polynomial[j - 1];
      }

      polynomial[0] = GALOIS_EXPONENT[modN(GALOIS_LOG[polynomial[0]] + i)];
    }

    // Use logs for generator polynomial to save calculation step.
    for (i = 0; i <= eccBlock; i++) {
      polynomial[i] = GALOIS_LOG[polynomial[i]];
    }

    // Append ECC to data buffer.
    k = x;
    y = 0;

    for (i = 0; i < neccBlock1; i++) {
      appendData(y, dataBlock, k, eccBlock);

      y += dataBlock;
      k += eccBlock;
    }

    for (i = 0; i < neccBlock2; i++) {
      appendData(y, dataBlock + 1, k, eccBlock);

      y += dataBlock + 1;
      k += eccBlock;
    }

    // Interleave blocks.
    y = 0;

    for (i = 0; i < dataBlock; i++) {
      for (j = 0; j < neccBlock1; j++) {
        eccBuffer[y++] = stringBuffer[i + j * dataBlock];
      }

      for (j = 0; j < neccBlock2; j++) {
        eccBuffer[y++] = stringBuffer[(neccBlock1 * dataBlock) + i + (j * (dataBlock + 1))];
      }
    }

    for (j = 0; j < neccBlock2; j++) {
      eccBuffer[y++] = stringBuffer[(neccBlock1 * dataBlock) + i + (j * (dataBlock + 1))];
    }

    for (i = 0; i < eccBlock; i++) {
      for (j = 0; j < neccBlock1 + neccBlock2; j++) {
        eccBuffer[y++] = stringBuffer[x + i + j * eccBlock];
      }
    }

    stringBuffer = eccBuffer;

    // Pack bits into frame avoiding masked area.
    x = y = width - 1;
    k = v = 1;

    // inteleaved data and ECC codes.
    m = (dataBlock + eccBlock) * (neccBlock1 + neccBlock2) + neccBlock2;

    for (i = 0; i < m; i++) {
      t = stringBuffer[i];

      for (j = 0; j < 8; j++, t <<= 1) {
        if (0x80 & t) {
          frameBuffer[x + width * y] = 1;
        }

        // Find next fill position.
        do {
          if (v) {
            x--;
          } else {
            x++;

            if (k) {
              if (y !== 0) {
                y--;
              } else {
                x -= 2;
                k  = !k;

                if (x === 6) {
                  x--;
                  y = 9;
                }
              }
            } else {
              if (y !== width - 1) {
                y++;
              } else {
                x -= 2;
                k  = !k;

                if (x === 6) {
                  x--;
                  y -= 8;
                }
              }
            }
          }

          v = !v;
        } while (isMasked(x, y));
      }
    }

    // Save pre-mask copy of frame.
    stringBuffer = frameBuffer.slice(0);

    t = 0;
    y = 30000;

    // Using `for` instead of `while` since in original Arduino code if an early mask was *good
    // enough* it wouldn't try for a better one since they get more complex and take longer.
    for (k = 0; k < 8; k++) {
      // Returns foreground-background imbalance.
      applyMask(k);

      x = checkBadness();

      // Is current mask better than previous best?
      if (x < y) {
        y = x;
        t = k;
      }

      // Don't increment `i` to a void redoing mask.
      if (t === 7) break;

      // Reset for next pass.
      frameBuffer = stringBuffer.slice(0);
    }

    // Redo best mask as none were *good enough* (i.e. last wasn't `t`).
    if (t !== k) {
      applyMask(t);
    }

    // Add in final mask/ECC level bytes.
    y = FINAL_FORMAT[t + ((eccLevel - 1) << 3)];

    // Low byte.
    for (k = 0; k < 8; k++, y >>= 1) {
      if (y & 1) {
        frameBuffer[(width - 1 - k) + width * 8] = 1;

        if (k < 6) {
          frameBuffer[8 + width * k] = 1;
        } else {
          frameBuffer[8 + width * (k + 1)] = 1;
        }
      }
    }

    // High byte.
    for (k = 0; k < 7; k++, y >>= 1) {
      if (y & 1) {
        frameBuffer[8 + width * (width - 7 + k)] = 1;

        if (k) {
          frameBuffer[(6 - k) + width * 8] = 1;
        } else {
          frameBuffer[7 + width * 8] = 1;
        }
      }
    }

    // Finally, return the image data.
    return frameBuffer;
  }

  // qr.js setup
  // -----------

  // Build the publicly exposed API.
  var qr = {

    // Constants
    // ---------

    // Current version of `qr`.
    VERSION: '1.1.3',

    // QR functions
    // ------------

    // Generate the QR code using the data provided and render it on to a `<canvas>` element.  
    // If no `<canvas>` element is specified in the argument provided a new one will be created and
    // used.  
    // ECC (error correction capacity) determines how many intential errors are contained in the QR
    // code.
    canvas: function(data) {
      data = normalizeData(data);

      // Module size of the generated QR code (i.e. 1-10).
      var size = data.size >= 1 && data.size <= 10 ? data.size : 4;
      // Actual size of the QR code symbol and is scaled to 25 pixels (e.g. 1 = 25px, 3 = 75px).
      size *= 25;

      // `<canvas>` element used to render the QR code.
      var cvs = data.canvas || createCanvas();
      // Retreive the 2D context of the canvas.
      var c2d = cvs.getContext('2d');
      // Ensure the canvas has the correct dimensions.
      c2d.canvas.width  = size;
      c2d.canvas.height = size;
      // Fill the canvas with the correct background colour.
      c2d.fillStyle = data.background || '#fff';
      c2d.fillRect(0, 0, size, size);

      // Determine the ECC level to be applied.
      eccLevel = ECC_LEVELS[(data.level && data.level.toUpperCase()) || 'L'];

      // Generate the image frame for the given `value`.
      var frame = generateFrame(data.value || '');

      c2d.lineWidth = 1;

      // Determine the *pixel* size.
      var px = size;
      px /= width;
      px  = Math.floor(px);

      // Draw the QR code.
      c2d.clearRect(0, 0, size, size);
      c2d.fillStyle = data.background || '#fff';
      c2d.fillRect(0, 0, px * (width + 8), px * (width + 8));
      c2d.fillStyle = data.foreground || '#000';

      var i, j;

      for (i = 0; i < width; i++) {
        for (j = 0; j < width; j++) {
          if (frame[j * width + i]) {
            c2d.fillRect(px * i, px * j, px, px);
          }
        }
      }

      return cvs;
    },

    // Generate the QR code using the data provided and render it on to a `<img>` element.  
    // If no `<img>` element is specified in the argument provided a new one will be created and
    // used.  
    // ECC (error correction capacity) determines how many intential errors are contained in the QR
    // code.
    image: function(data) {
      data = normalizeData(data);

      // `<canvas>` element only which the QR code is rendered.
      var cvs = this.canvas(data);
      // `<img>` element used to display the QR code.
      var img = data.image || createImage();

      // Apply the QR code to `img`.
      img.src    = cvs.toDataURL(data.mime || DEFAULT_MIME);
      img.height = cvs.height;
      img.width  = cvs.width;

      return img;
    },

    // Generate the QR code using the data provided and render it on to a `<canvas>` element and
    // save it as an image file.  
    // If no `<canvas>` element is specified in the argument provided a new one will be created and
    // used.  
    // ECC (error correction capacity) determines how many intential errors are contained in the QR
    // code.  
    // If called in a browser the `path` property/argument is ignored and will simply prompt the
    // user to choose a location and file name. However, if called within node.js the file will be
    // saved to specified path.  
    // A `callback` function must be provided which will be called once the saving process has
    // started. If an error occurs it will be passed as the first argument to this function,
    // otherwise this argument will be `null`.
    save: function(data, path, callback) {
      data = normalizeData(data);

      switch (typeof path) {
        case 'function':
          callback = path;
          path = null;
          break;
        case 'string':
          data.path = path;
          break;
      }

      // Callback function is required.
      if (typeof callback !== 'function') {
        throw new TypeError('Invalid callback type: ' + typeof callback);
      }

      var completed = false;
      // `<canvas>` element only which the QR code is rendered.
      var cvs = this.canvas(data);

      // Simple function to try and ensure that the `callback` function is only called once.
      function done(error) {
        if (!completed) {
          completed = true;

          callback(error);
        }
      }

      if (inNode) {
        writeFile(cvs, data, done);
      } else {
        download(cvs, data, done);
      }
    },

    // Generate the QR code using the data provided and render it on to a `<canvas>` element and
    // save it as an image file.  
    // If no `<canvas>` element is specified in the argument provided a new one will be created and
    // used.  
    // ECC (error correction capacity) determines how many intential errors are contained in the QR
    // code.  
    // If called in a browser the `path` property/argument is ignored and will simply prompt the
    // user to choose a location and file name. However, if called within node.js the file will be
    // saved to specified path.
    saveSync: function(data, path) {
      data = normalizeData(data);

      if (typeof path === 'string') data.path = path;

      // `<canvas>` element only which the QR code is rendered.
      var cvs = this.canvas(data);

      if (inNode) {
        writeFileSync(cvs, data);
      } else {
        download(cvs, data);
      }
    },

    // Generate the QR code using the data provided and render it on to a `<canvas>` element before
    // returning its data URI.  
    // If no `<canvas>` element is specified in the argument provided a new one will be created and
    // used.  
    // ECC (error correction capacity) determines how many intential errors are contained in the QR
    // code.
    toDataURL: function(data) {
      data = normalizeData(data);

      return this.canvas(data).toDataURL(data.mime || DEFAULT_MIME);
    },

    // Utility functions
    // -----------------

    // Run qr.js in *noConflict* mode, returning the `qr` variable to its previous owner.  
    // Returns a reference to `qr`.
    noConflict: function() {
      root.qr = previousQr;
      return this;
    }

  };

  // Support
  // -------

  // Export `qr` for node.js and CommonJS.
  if (typeof exports !== 'undefined') {
    inNode = true;

    if (typeof module !== 'undefined' && module.exports) {
      exports = module.exports = qr;
    }
    exports.qr = qr;

    // Import required node.js modules.
    Canvas = require('canvas');
    Image = Canvas.Image;
    fs = require('fs');
  } else if (typeof define === 'function' && define.amd) {
    define(function () {
      return qr;
    });
  } else {
    // In non-HTML5 browser so strip base functionality.
    if (!root.HTMLCanvasElement) {
      overrideAPI(qr);
    }

    root.qr = qr;
  }

})(this);
