pdf.js/web/text_layer_builder.js

/* Copyright 2012 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.
 */

import { getGlobalEventBus } from './dom_events';
import { renderTextLayer } from 'pdfjs-lib';

var EXPAND_DIVS_TIMEOUT = 300; // ms

/**
 * @typedef {Object} TextLayerBuilderOptions
 * @property {HTMLDivElement} textLayerDiv - The text layer container.
 * @property {EventBus} eventBus - The application event bus.
 * @property {number} pageIndex - The page index.
 * @property {PageViewport} viewport - The viewport of the text layer.
 * @property {PDFFindController} findController
 * @property {boolean} enhanceTextSelection - Option to turn on improved
 *   text selection.
 */

/**
 * TextLayerBuilder provides text-selection functionality for the PDF.
 * It does this by creating overlay divs over the PDF text. These divs
 * contain text that matches the PDF text they are overlaying. This object
 * also provides a way to highlight text that is being searched for.
 * @class
 */
var TextLayerBuilder = (function TextLayerBuilderClosure() {
  function TextLayerBuilder(options) {
    this.textLayerDiv = options.textLayerDiv;
    this.eventBus = options.eventBus || getGlobalEventBus();
    this.textContent = null;
    this.textContentItemsStr = [];
    this.textContentStream = null;
    this.renderingDone = false;
    this.pageIdx = options.pageIndex;
    this.pageNumber = this.pageIdx + 1;
    this.matches = [];
    this.viewport = options.viewport;
    this.textDivs = [];
    this.findController = options.findController || null;
    this.textLayerRenderTask = null;
    this.enhanceTextSelection = options.enhanceTextSelection;
    this._bindMouse();
  }

  TextLayerBuilder.prototype = {
    /**
     * @private
     */
    _finishRendering: function TextLayerBuilder_finishRendering() {
      this.renderingDone = true;

      if (!this.enhanceTextSelection) {
        var endOfContent = document.createElement('div');
        endOfContent.className = 'endOfContent';
        this.textLayerDiv.appendChild(endOfContent);
      }

      this.eventBus.dispatch('textlayerrendered', {
        source: this,
        pageNumber: this.pageNumber,
        numTextDivs: this.textDivs.length,
      });
    },

    /**
     * Renders the text layer.
     * @param {number} timeout (optional) if specified, the rendering waits
     *   for specified amount of ms.
     */
    render: function TextLayerBuilder_render(timeout) {
      if (!(this.textContent || this.textContentStream) || this.renderingDone) {
        return;
      }
      this.cancel();

      this.textDivs = [];
      var textLayerFrag = document.createDocumentFragment();
      this.textLayerRenderTask = renderTextLayer({
        textContent: this.textContent,
        textContentStream: this.textContentStream,
        container: textLayerFrag,
        viewport: this.viewport,
        textDivs: this.textDivs,
        textContentItemsStr: this.textContentItemsStr,
        timeout,
        enhanceTextSelection: this.enhanceTextSelection,
      });
      this.textLayerRenderTask.promise.then(() => {
        this.textLayerDiv.appendChild(textLayerFrag);
        this._finishRendering();
        this.updateMatches();
      }, function (reason) {
        // cancelled or failed to render text layer -- skipping errors
      });
    },

    /**
     * Cancels rendering of the text layer.
     */
    cancel: function TextLayerBuilder_cancel() {
      if (this.textLayerRenderTask) {
        this.textLayerRenderTask.cancel();
        this.textLayerRenderTask = null;
      }
    },

    setTextContentStream(readableStream) {
      this.cancel();
      this.textContentStream = readableStream;
    },

    setTextContent: function TextLayerBuilder_setTextContent(textContent) {
      this.cancel();
      this.textContent = textContent;
    },

    convertMatches: function TextLayerBuilder_convertMatches(matches,
                                                             matchesLength) {
      var i = 0;
      var iIndex = 0;
      let textContentItemsStr = this.textContentItemsStr;
      var end = textContentItemsStr.length - 1;
      var queryLen = (this.findController === null ?
                      0 : this.findController.state.query.length);
      var ret = [];
      if (!matches) {
        return ret;
      }
      for (var m = 0, len = matches.length; m < len; m++) {
        // Calculate the start position.
        var matchIdx = matches[m];

        // Loop over the divIdxs.
        while (i !== end && matchIdx >=
               (iIndex + textContentItemsStr[i].length)) {
          iIndex += textContentItemsStr[i].length;
          i++;
        }

        if (i === textContentItemsStr.length) {
          console.error('Could not find a matching mapping');
        }

        var match = {
          begin: {
            divIdx: i,
            offset: matchIdx - iIndex,
          },
        };

        // Calculate the end position.
        if (matchesLength) { // multiterm search
          matchIdx += matchesLength[m];
        } else { // phrase search
          matchIdx += queryLen;
        }

        // Somewhat the same array as above, but use > instead of >= to get
        // the end position right.
        while (i !== end && matchIdx >
               (iIndex + textContentItemsStr[i].length)) {
          iIndex += textContentItemsStr[i].length;
          i++;
        }

        match.end = {
          divIdx: i,
          offset: matchIdx - iIndex,
        };
        ret.push(match);
      }

      return ret;
    },

    renderMatches: function TextLayerBuilder_renderMatches(matches) {
      // Early exit if there is nothing to render.
      if (matches.length === 0) {
        return;
      }

      let textContentItemsStr = this.textContentItemsStr;
      var textDivs = this.textDivs;
      var prevEnd = null;
      var pageIdx = this.pageIdx;
      var isSelectedPage = (this.findController === null ?
        false : (pageIdx === this.findController.selected.pageIdx));
      var selectedMatchIdx = (this.findController === null ?
                              -1 : this.findController.selected.matchIdx);
      var highlightAll = (this.findController === null ?
                          false : this.findController.state.highlightAll);
      var infinity = {
        divIdx: -1,
        offset: undefined,
      };

      function beginText(begin, className) {
        var divIdx = begin.divIdx;
        textDivs[divIdx].textContent = '';
        appendTextToDiv(divIdx, 0, begin.offset, className);
      }

      function appendTextToDiv(divIdx, fromOffset, toOffset, className) {
        var div = textDivs[divIdx];
        var content =
          textContentItemsStr[divIdx].substring(fromOffset, toOffset);
        var node = document.createTextNode(content);
        if (className) {
          var span = document.createElement('span');
          span.className = className;
          span.appendChild(node);
          div.appendChild(span);
          return;
        }
        div.appendChild(node);
      }

      var i0 = selectedMatchIdx, i1 = i0 + 1;
      if (highlightAll) {
        i0 = 0;
        i1 = matches.length;
      } else if (!isSelectedPage) {
        // Not highlighting all and this isn't the selected page, so do nothing.
        return;
      }

      for (var i = i0; i < i1; i++) {
        var match = matches[i];
        var begin = match.begin;
        var end = match.end;
        var isSelected = (isSelectedPage && i === selectedMatchIdx);
        var highlightSuffix = (isSelected ? ' selected' : '');

        if (this.findController) {
          this.findController.updateMatchPosition(pageIdx, i, textDivs,
                                                  begin.divIdx);
        }

        // Match inside new div.
        if (!prevEnd || begin.divIdx !== prevEnd.divIdx) {
          // If there was a previous div, then add the text at the end.
          if (prevEnd !== null) {
            appendTextToDiv(prevEnd.divIdx, prevEnd.offset, infinity.offset);
          }
          // Clear the divs and set the content until the starting point.
          beginText(begin);
        } else {
          appendTextToDiv(prevEnd.divIdx, prevEnd.offset, begin.offset);
        }

        if (begin.divIdx === end.divIdx) {
          appendTextToDiv(begin.divIdx, begin.offset, end.offset,
                          'highlight' + highlightSuffix);
        } else {
          appendTextToDiv(begin.divIdx, begin.offset, infinity.offset,
                          'highlight begin' + highlightSuffix);
          for (var n0 = begin.divIdx + 1, n1 = end.divIdx; n0 < n1; n0++) {
            textDivs[n0].className = 'highlight middle' + highlightSuffix;
          }
          beginText(end, 'highlight end' + highlightSuffix);
        }
        prevEnd = end;
      }

      if (prevEnd) {
        appendTextToDiv(prevEnd.divIdx, prevEnd.offset, infinity.offset);
      }
    },

    updateMatches: function TextLayerBuilder_updateMatches() {
      // Only show matches when all rendering is done.
      if (!this.renderingDone) {
        return;
      }

      // Clear all matches.
      var matches = this.matches;
      var textDivs = this.textDivs;
      let textContentItemsStr = this.textContentItemsStr;
      var clearedUntilDivIdx = -1;

      // Clear all current matches.
      for (var i = 0, len = matches.length; i < len; i++) {
        var match = matches[i];
        var begin = Math.max(clearedUntilDivIdx, match.begin.divIdx);
        for (var n = begin, end = match.end.divIdx; n <= end; n++) {
          var div = textDivs[n];
          div.textContent = textContentItemsStr[n];
          div.className = '';
        }
        clearedUntilDivIdx = match.end.divIdx + 1;
      }

      if (this.findController === null || !this.findController.active) {
        return;
      }

      // Convert the matches on the page controller into the match format
      // used for the textLayer.
      var pageMatches, pageMatchesLength;
      if (this.findController !== null) {
        pageMatches = this.findController.pageMatches[this.pageIdx] || null;
        pageMatchesLength = (this.findController.pageMatchesLength) ?
          this.findController.pageMatchesLength[this.pageIdx] || null : null;
      }

      this.matches = this.convertMatches(pageMatches, pageMatchesLength);
      this.renderMatches(this.matches);
    },

    /**
     * Fixes text selection: adds additional div where mouse was clicked.
     * This reduces flickering of the content if mouse slowly dragged down/up.
     * @private
     */
    _bindMouse: function TextLayerBuilder_bindMouse() {
      var div = this.textLayerDiv;
      var self = this;
      var expandDivsTimer = null;

      div.addEventListener('mousedown', function (e) {
        if (self.enhanceTextSelection && self.textLayerRenderTask) {
          self.textLayerRenderTask.expandTextDivs(true);
          if ((typeof PDFJSDev === 'undefined' ||
               !PDFJSDev.test('FIREFOX || MOZCENTRAL')) &&
              expandDivsTimer) {
            clearTimeout(expandDivsTimer);
            expandDivsTimer = null;
          }
          return;
        }
        var end = div.querySelector('.endOfContent');
        if (!end) {
          return;
        }
        if (typeof PDFJSDev === 'undefined' ||
            !PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
        // On non-Firefox browsers, the selection will feel better if the height
        // of the endOfContent div will be adjusted to start at mouse click
        // location -- this will avoid flickering when selections moves up.
        // However it does not work when selection started on empty space.
        var adjustTop = e.target !== div;
        if (typeof PDFJSDev === 'undefined' || PDFJSDev.test('GENERIC')) {
          adjustTop = adjustTop && window.getComputedStyle(end).
            getPropertyValue('-moz-user-select') !== 'none';
        }
        if (adjustTop) {
          var divBounds = div.getBoundingClientRect();
          var r = Math.max(0, (e.pageY - divBounds.top) / divBounds.height);
          end.style.top = (r * 100).toFixed(2) + '%';
        }
        }
        end.classList.add('active');
      });

      div.addEventListener('mouseup', function (e) {
        if (self.enhanceTextSelection && self.textLayerRenderTask) {
          if (typeof PDFJSDev === 'undefined' ||
              !PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
            expandDivsTimer = setTimeout(function() {
              if (self.textLayerRenderTask) {
                self.textLayerRenderTask.expandTextDivs(false);
              }
              expandDivsTimer = null;
            }, EXPAND_DIVS_TIMEOUT);
          } else {
            self.textLayerRenderTask.expandTextDivs(false);
          }
          return;
        }
        var end = div.querySelector('.endOfContent');
        if (!end) {
          return;
        }
        if (typeof PDFJSDev === 'undefined' ||
            !PDFJSDev.test('FIREFOX || MOZCENTRAL')) {
          end.style.top = '';
        }
        end.classList.remove('active');
      });
    },
  };
  return TextLayerBuilder;
})();

/**
 * @constructor
 * @implements IPDFTextLayerFactory
 */
function DefaultTextLayerFactory() {}
DefaultTextLayerFactory.prototype = {
  /**
   * @param {HTMLDivElement} textLayerDiv
   * @param {number} pageIndex
   * @param {PageViewport} viewport
   * @param {boolean} enhanceTextSelection
   * @returns {TextLayerBuilder}
   */
  createTextLayerBuilder(textLayerDiv, pageIndex, viewport,
                         enhanceTextSelection = false) {
    return new TextLayerBuilder({
      textLayerDiv,
      pageIndex,
      viewport,
      enhanceTextSelection,
    });
  },
};

export {
  TextLayerBuilder,
  DefaultTextLayerFactory,
};