mozPrintCallback_polyfill.js

/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
/* Copyright 2013 Mozilla Foundation
 *
 * 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.
 */
/* globals HTMLCanvasElement */

'use strict';
(function mozPrintCallbackPolyfillClosure() {
  if ('mozPrintCallback' in document.createElement('canvas')) {
    return;
  }
  // Cause positive result on feature-detection:
  HTMLCanvasElement.prototype.mozPrintCallback = undefined;

  var canvases;   // During print task: non-live NodeList of <canvas> elements
  var index;      // Index of <canvas> element that is being processed

  var print = window.print;
  window.print = function print() {
    if (canvases) {
      console.warn('Ignored window.print() because of a pending print job.');
      return;
    }
    try {
      dispatchEvent('beforeprint');
    } finally {
      canvases = document.querySelectorAll('canvas');
      index = -1;
      next();
    }
  };

  function dispatchEvent(eventType) {
    var event = document.createEvent('CustomEvent');
    event.initCustomEvent(eventType, false, false, 'custom');
    window.dispatchEvent(event);
  }

  function next() {
    if (!canvases) {
      return; // Print task cancelled by user (state reset in abort())
    }

    renderProgress();
    if (++index < canvases.length) {
      var canvas = canvases[index];
      if (typeof canvas.mozPrintCallback === 'function') {
        canvas.mozPrintCallback({
          context: canvas.getContext('2d'),
          abort: abort,
          done: next
        });
      } else {
        next();
      }
    } else {
      renderProgress();
      print.call(window);
      setTimeout(abort, 20); // Tidy-up
    }
  }

  function abort() {
    if (canvases) {
      canvases = null;
      renderProgress();
      dispatchEvent('afterprint');
    }
  }

  function renderProgress() {
    var progressContainer = document.getElementById('mozPrintCallback-shim');
    if (canvases) {
      var progress = Math.round(100 * index / canvases.length);
      var progressBar = progressContainer.querySelector('progress');
      var progressPerc = progressContainer.querySelector('.relative-progress');
      progressBar.value = progress;
      progressPerc.textContent = progress + '%';
      progressContainer.removeAttribute('hidden');
      progressContainer.onclick = abort;
    } else {
      progressContainer.setAttribute('hidden', '');
    }
  }

  var hasAttachEvent = !!document.attachEvent;

  window.addEventListener('keydown', function(event) {
    // Intercept Cmd/Ctrl + P in all browsers.
    // Also intercept Cmd/Ctrl + Shift + P in Chrome and Opera
    if (event.keyCode === 80/*P*/ && (event.ctrlKey || event.metaKey) &&
        !event.altKey && (!event.shiftKey || window.chrome || window.opera)) {
      window.print();
      if (hasAttachEvent) {
        // Only attachEvent can cancel Ctrl + P dialog in IE <=10
        // attachEvent is gone in IE11, so the dialog will re-appear in IE11.
        return;
      }
      event.preventDefault();
      if (event.stopImmediatePropagation) {
        event.stopImmediatePropagation();
      } else {
        event.stopPropagation();
      }
      return;
    }
    if (event.keyCode === 27 && canvases) { // Esc
      abort();
    }
  }, true);
  if (hasAttachEvent) {
    document.attachEvent('onkeydown', function(event) {
      event = event || window.event;
      if (event.keyCode === 80/*P*/ && event.ctrlKey) {
        event.keyCode = 0;
        return false;
      }
    });
  }

  if ('onbeforeprint' in window) {
    // Do not propagate before/afterprint events when they are not triggered
    // from within this polyfill. (FF/IE).
    var stopPropagationIfNeeded = function(event) {
      if (event.detail !== 'custom' && event.stopImmediatePropagation) {
        event.stopImmediatePropagation();
      }
    };
    window.addEventListener('beforeprint', stopPropagationIfNeeded, false);
    window.addEventListener('afterprint', stopPropagationIfNeeded, false);
  }
})();