worker.js

import jsPDF from 'jspdf';
import html2canvas from 'html2canvas';
import { objType, createElement, cloneNode, toPx } from './utils.js';

/* ----- CONSTRUCTOR ----- */

var Worker = function Worker(opt) {
  // Create the root parent for the proto chain, and the starting Worker.
  var root = Object.assign(Worker.convert(Promise.resolve()),
                           JSON.parse(JSON.stringify(Worker.template)));
  var self = Worker.convert(Promise.resolve(), root);

  // Set progress, optional settings, and return.
  self = self.setProgress(1, Worker, 1, [Worker]);
  self = self.set(opt);
  return self;
};

// Boilerplate for subclassing Promise.
Worker.prototype = Object.create(Promise.prototype);
Worker.prototype.constructor = Worker;

// Converts/casts promises into Workers.
Worker.convert = function convert(promise, inherit) {
  // Uses prototypal inheritance to receive changes made to ancestors' properties.
  promise.__proto__ = inherit || Worker.prototype;
  return promise;
};

Worker.template = {
  prop: {
    src: null,
    canvas: null,
    img: null,
    pdf: null,
    pageSize: null
  },
  progress: {
    val: 0,
    state: null,
    n: 0,
    stack: []
  },
  opt: {
    filename: 'file.pdf',
    margin: [0,0,0,0],
    image: { type: 'jpeg', quality: 0.95 },
    enableLinks: true,
    html2canvas: {},
    jsPDF: {}
  }
};

/* ----- FROM / TO ----- */

Worker.prototype.from = function from(src, type) {
  function getType(src) {
    switch (objType(src)) {
      case 'string':  return 'string';
      case 'element': return src.nodeName.toLowerCase === 'canvas' ? 'canvas' : 'element';
      default:        return 'unknown';
    }
  }

  return this.then(function from_main() {
    type = type || getType(src);
    switch (type) {
      case 'string':  return this.set({ src: createElement('div', {innerHTML: src}) });
      case 'element': return this.set({ src: src });
      case 'canvas':  return this.set({ canvas: src });
      case 'img':     return this.set({ img: src });
      default:        return this.error('Unknown source type.');
    }
  });
};

Worker.prototype.to = function to(target) {
  // Route the 'to' request to the appropriate method.
  switch (target) {
    case 'canvas':
      return this.toCanvas();
    case 'img':
      return this.toImg();
    case 'pdf':
      return this.toPdf();
    default:
      return this.error('Invalid target.');
  }
};

Worker.prototype.toCanvas = function toCanvas() {
  // Set up function prerequisites.
  var prereqs = [
    function checkSrc() { return this.prop.src || this.error('Cannot duplicate - no source HTML.'); },
    function checkPageSize() { return this.prop.pageSize || this.setPageSize(); }
  ];

  // Fulfill prereqs then create the canvas.
  return this.thenList(prereqs).then(function toCanvas_main() {
    // Handle old-fashioned 'onrendered' argument.
    var options = Object.assign({}, this.opt.html2canvas);
    delete options.onrendered;

    // Alter html2canvas options for reflow behaviour.
    var src = this.prop.src;
    var ignoreElements_orig = options.ignoreElements || function () {};
    options.ignoreElements = function (el) {
      // List of metadata tags:   https://www.w3schools.com/html/html_head.asp
      var metaTags = ['HEAD', 'TITLE', 'BASE', 'LINK', 'META', 'SCRIPT', 'STYLE'];
      var toClone = metaTags.indexOf(el.tagName) !== -1 || el.contains(src) || src.contains(el);
      return !toClone || ignoreElements_orig(el);
    }
    options.windowWidth = this.prop.pageSize.inner.px.width;
    options.width = options.windowWidth;

    return html2canvas(src, options);
  }).then(function toCanvas_post(canvas) {
    // Handle old-fashioned 'onrendered' argument.
    var onRendered = this.opt.html2canvas.onrendered || function () {};
    onRendered(canvas);

    this.prop.canvas = canvas;
  });
};

Worker.prototype.toImg = function toImg() {
  // Set up function prerequisites.
  var prereqs = [
    function checkCanvas() { return this.prop.canvas || this.toCanvas(); }
  ];

  // Fulfill prereqs then create the image.
  return this.thenList(prereqs).then(function toImg_main() {
    var imgData = this.prop.canvas.toDataURL('image/' + this.opt.image.type, this.opt.image.quality);
    this.prop.img = document.createElement('img');
    this.prop.img.src = imgData;
  });
};

Worker.prototype.toPdf = function toPdf() {
  // Set up function prerequisites.
  var prereqs = [
    function checkCanvas() { return this.prop.canvas || this.toCanvas(); }
  ];

  // Fulfill prereqs then create the image.
  return this.thenList(prereqs).then(function toPdf_main() {
    // Create local copies of frequently used properties.
    var canvas = this.prop.canvas;
    var opt = this.opt;

    // Calculate the number of pages.
    var ctx = canvas.getContext('2d');
    var pxFullHeight = canvas.height;
    var pxPageHeight = Math.floor(canvas.width * this.prop.pageSize.inner.ratio);
    var nPages = Math.ceil(pxFullHeight / pxPageHeight);

    // Define pageHeight separately so it can be trimmed on the final page.
    var pageHeight = this.prop.pageSize.inner.height;

    // Create a one-page canvas to split up the full image.
    var pageCanvas = document.createElement('canvas');
    var pageCtx = pageCanvas.getContext('2d');
    pageCanvas.width = canvas.width;
    pageCanvas.height = pxPageHeight;

    // Initialize the PDF.
    this.prop.pdf = this.prop.pdf || new jsPDF(opt.jsPDF);

    for (var page=0; page<nPages; page++) {
      // Trim the final page to reduce file size.
      if (page === nPages-1 && pxFullHeight % pxPageHeight !== 0) {
        pageCanvas.height = pxFullHeight % pxPageHeight;
        pageHeight = pageCanvas.height * this.prop.pageSize.inner.width / pageCanvas.width;
      }

      // Display the page.
      var w = pageCanvas.width;
      var h = pageCanvas.height;
      pageCtx.fillStyle = 'white';
      pageCtx.fillRect(0, 0, w, h);
      pageCtx.drawImage(canvas, 0, page*pxPageHeight, w, h, 0, 0, w, h);

      // Add the page to the PDF.
      if (page)  this.prop.pdf.addPage();
      var imgData = pageCanvas.toDataURL('image/' + opt.image.type, opt.image.quality);
      this.prop.pdf.addImage(imgData, opt.image.type, opt.margin[1], opt.margin[0],
                        this.prop.pageSize.inner.width, pageHeight);
    }
  });
};


/* ----- OUTPUT / SAVE ----- */

Worker.prototype.output = function output(type, options, src) {
  // Redirect requests to the correct function (outputPdf / outputImg).
  src = src || 'pdf';
  if (src.toLowerCase() === 'img' || src.toLowerCase() === 'image') {
    return this.outputImg(type, options);
  } else {
    return this.outputPdf(type, options);
  }
};

Worker.prototype.outputPdf = function outputPdf(type, options) {
  // Set up function prerequisites.
  var prereqs = [
    function checkPdf() { return this.prop.pdf || this.toPdf(); }
  ];

  // Fulfill prereqs then perform the appropriate output.
  return this.thenList(prereqs).then(function outputPdf_main() {
    /* Currently implemented output types:
     *    https://rawgit.com/MrRio/jsPDF/master/docs/jspdf.js.html#line992
     *  save(options), arraybuffer, blob, bloburi/bloburl,
     *  datauristring/dataurlstring, dataurlnewwindow, datauri/dataurl
     */
    return this.prop.pdf.output(type, options);
  });
};

Worker.prototype.outputImg = function outputImg(type, options) {
  // Set up function prerequisites.
  var prereqs = [
    function checkImg() { return this.prop.img || this.toImg(); }
  ];

  // Fulfill prereqs then perform the appropriate output.
  return this.thenList(prereqs).then(function outputImg_main() {
    switch (type) {
      case undefined:
      case 'img':
        return this.prop.img;
      case 'datauristring':
      case 'dataurlstring':
        return this.prop.img.src;
      case 'datauri':
      case 'dataurl':
        return document.location.href = this.prop.img.src;
      default:
        throw 'Image output type "' + type + '" is not supported.';
    }
  });
};

Worker.prototype.save = function save(filename) {
  // Set up function prerequisites.
  var prereqs = [
    function checkPdf() { return this.prop.pdf || this.toPdf(); }
  ];

  // Fulfill prereqs, update the filename (if provided), and save the PDF.
  return this.thenList(prereqs).set(
    filename ? { filename: filename } : null
  ).then(function save_main() {
    this.prop.pdf.save(this.opt.filename);
  });
};

/* ----- SET / GET ----- */

Worker.prototype.set = function set(opt) {
  // TODO: Implement ordered pairs?

  // Silently ignore invalid or empty input.
  if (objType(opt) !== 'object') {
    return this;
  }

  // Build an array of setter functions to queue.
  var fns = Object.keys(opt || {}).map(function (key) {
      if (key in Worker.template.prop) {
        // Set pre-defined properties.
        return function set_prop() { this.prop[key] = opt[key]; }
      } else {
        switch (key) {
          case 'margin':
            return this.setMargin.bind(this, opt.margin);
          case 'jsPDF':
            return function set_jsPDF() { this.opt.jsPDF = opt.jsPDF; return this.setPageSize(); }
          case 'pageSize':
            return this.setPageSize.bind(this, opt.pageSize);
          default:
            // Set any other properties in opt.
            return function set_opt() { this.opt[key] = opt[key] };
        }
      }
  }, this);

  // Set properties within the promise chain.
  return this.then(function set_main() {
    return this.thenList(fns);
  });
};

Worker.prototype.get = function get(key, cbk) {
  return this.then(function get_main() {
    // Fetch the requested property, either as a predefined prop or in opt.
    var val = (key in Worker.template.prop) ? this.prop[key] : this.opt[key];
    return cbk ? cbk(val) : val;
  });
};

Worker.prototype.setMargin = function setMargin(margin) {
  return this.then(function setMargin_main() {
    // Parse the margin property: [top, left, bottom, right].
    switch (objType(margin)) {
      case 'number':
        margin = [margin, margin, margin, margin];
      case 'array':
        if (margin.length === 2) {
          margin = [margin[0], margin[1], margin[0], margin[1]];
        }
        if (margin.length === 4) {
          break;
        }
      default:
        return this.error('Invalid margin array.');
    }

    // Set the margin property, then update pageSize.
    this.opt.margin = margin;
  }).then(this.setPageSize);
}

Worker.prototype.setPageSize = function setPageSize(pageSize) {
  return this.then(function setPageSize_main() {
    // Retrieve page-size based on jsPDF settings, if not explicitly provided.
    pageSize = pageSize || jsPDF.getPageSize(this.opt.jsPDF);

    // Add 'inner' field if not present.
    if (!pageSize.hasOwnProperty('inner')) {
      pageSize.inner = {
        width:  pageSize.width - this.opt.margin[1] - this.opt.margin[3],
        height: pageSize.height - this.opt.margin[0] - this.opt.margin[2]
      };
      pageSize.inner.px = {
        width:  toPx(pageSize.inner.width, pageSize.k),
        height: toPx(pageSize.inner.height, pageSize.k)
      };
      pageSize.inner.ratio = pageSize.inner.height / pageSize.inner.width;
    }

    // Attach pageSize to this.
    this.prop.pageSize = pageSize;
  });
}

Worker.prototype.setProgress = function setProgress(val, state, n, stack) {
  // Immediately update all progress values.
  if (val != null)    this.progress.val = val;
  if (state != null)  this.progress.state = state;
  if (n != null)      this.progress.n = n;
  if (stack != null)  this.progress.stack = stack;
  this.progress.ratio = this.progress.val / this.progress.state;

  // Return this for command chaining.
  return this;
};

Worker.prototype.updateProgress = function updateProgress(val, state, n, stack) {
  // Immediately update all progress values, using setProgress.
  return this.setProgress(
    val ? this.progress.val + val : null,
    state ? state : null,
    n ? this.progress.n + n : null,
    stack ? this.progress.stack.concat(stack) : null
  );
};

/* ----- PROMISE MAPPING ----- */

Worker.prototype.then = function then(onFulfilled, onRejected) {
  // Wrap `this` for encapsulation.
  var self = this;

  return this.thenCore(onFulfilled, onRejected, function then_main(onFulfilled, onRejected) {
    // Update progress while queuing, calling, and resolving `then`.
    self.updateProgress(null, null, 1, [onFulfilled]);
    return Promise.prototype.then.call(this, function then_pre(val) {
      self.updateProgress(null, onFulfilled);
      return val;
    }).then(onFulfilled, onRejected).then(function then_post(val) {
      self.updateProgress(1);
      return val;
    });
  });
};

Worker.prototype.thenCore = function thenCore(onFulfilled, onRejected, thenBase) {
  // Handle optional thenBase parameter.
  thenBase = thenBase || Promise.prototype.then;

  // Wrap `this` for encapsulation and bind it to the promise handlers.
  var self = this;
  if (onFulfilled)  { onFulfilled = onFulfilled.bind(self); }
  if (onRejected)   { onRejected = onRejected.bind(self); }

  // Cast self into a Promise to avoid polyfills recursively defining `then`.
  var isNative = Promise.toString().indexOf('[native code]') !== -1 && Promise.name === 'Promise';
  var selfPromise = isNative ? self : Worker.convert(Object.assign({}, self), Promise.prototype);

  // Return the promise, after casting it into a Worker and preserving props.
  var returnVal = thenBase.call(selfPromise, onFulfilled, onRejected);
  return Worker.convert(returnVal, self.__proto__);
};

Worker.prototype.thenExternal = function thenExternal(onFulfilled, onRejected) {
  // Call `then` and return a standard promise (exits the Worker chain).
  return Promise.prototype.then.call(this, onFulfilled, onRejected);
};

Worker.prototype.thenList = function thenList(fns) {
  // Queue a series of promise 'factories' into the promise chain.
  var self = this;
  fns.forEach(function thenList_forEach(fn) {
    self = self.thenCore(fn);
  });
  return self;
};

Worker.prototype['catch'] = function (onRejected) {
  // Bind `this` to the promise handler, call `catch`, and return a Worker.
  if (onRejected)   { onRejected = onRejected.bind(this); }
  var returnVal = Promise.prototype['catch'].call(this, onRejected);
  return Worker.convert(returnVal, this);
};

Worker.prototype.catchExternal = function catchExternal(onRejected) {
  // Call `catch` and return a standard promise (exits the Worker chain).
  return Promise.prototype['catch'].call(this, onRejected);
};

Worker.prototype.error = function error(msg) {
  // Throw the error in the Promise chain.
  return this.then(function error_main() {
    throw new Error(msg);
  });
};


/* ----- ALIASES ----- */

Worker.prototype.using = Worker.prototype.set;
Worker.prototype.saveAs = Worker.prototype.save;
Worker.prototype.export = Worker.prototype.output;
Worker.prototype.run = Worker.prototype.then;


/* ----- FINISHING ----- */

// Expose the Worker class.
export default Worker;