Filter: deduplicate annotations before filtering

If there are many spans of text for an annotation (many table cells,
say), previously the filter would be applied once for each span, and
matching annotations would appear n times in filter.annotations. In and
of itself this is relatively harmless, but filterHighlights then maps
back from annotations to highlights, and:

    for (var i = 0, len = filtered.length; i < len; i++) {
         highlights = highlights.not(filtered[i]._local.highlights);
    }

is ruinous. This change dramatically improves filtering performance on
my pet test case of big, overlapping highlights on a 5000×3 table.

I have mixed feelings about using a new identifier in _local for this,
but we don't have any guarantee that the id provided by the server is
unique, or even present.

I also have mixed feelings about setting the id in highlighter.js and
using it in filter.js, but the same coupling exists for
.data('annotation') already...

src/ui/filter.js

@@ -160,10 +160,14 @@ Filter.prototype.updateFilter = function (filter) {
         return;
     }
 
-    var annotations = this.highlights.map(function () {
-        return $(this).data('annotation');
-    });
-    annotations = $.makeArray(annotations);
+    var annotations = (function (highlights) {
+        var annotationsById = {};
+        highlights.each(function () {
+            var a = $(this).data('annotation');
+            annotationsById[a._local.id] = a;
+        });
+        return $.map(annotationsById, function(a) { return a; });
+    }(this.highlights));
 
     for (var i = 0, len = annotations.length; i < len; i++) {
         var annotation = annotations[i],

src/ui/highlighter.js

@@ -119,6 +119,15 @@ Highlighter.prototype.drawAll = function (annotations) {
     return p;
 };
 
+// local unique IDs for annotations, used to deduplicate when recovering them
+// from highlights.
+var id = (function () {
+    var counter = 0;
+    return function() {
+        return '_local_id_' + (++counter);
+    }
+}());
+
 // Public: Draw highlights for the annotation.
 //
 // annotation - An annotation Object for which to draw highlights.
@@ -144,6 +153,11 @@ Highlighter.prototype.draw = function (annotation) {
     if (!hasHighlights) {
         annotation._local.highlights = [];
     }
+    var hasLocalId = (typeof annotation._local.id !== 'undefined' &&
+                      annotation._local.id === null);
+    if (!hasLocalId) {
+        annotation._local.id = id();
+    }
 
     for (var j = 0, jlen = normedRanges.length; j < jlen; j++) {
         var normed = normedRanges[j];

test/spec/ui/filter_spec.js

@@ -125,10 +125,14 @@ describe('ui.filter.Filter', function () {
             };
             annotations = [{text: 'cat'}, {text: 'dog'}, {text: 'car'}];
             $.each(annotations, function(i, annotation) {
-                $('<span class="annotator-hl">')
-                    .text(annotation)
-                    .data('annotation', annotation)
-                    .appendTo(element);
+                this._local = {id: this.text};
+                for (var j = 0; j < annotation.text.length; j++) {
+                    var ch = annotation.text[j]
+                    $('<span class="annotator-hl">')
+                        .text(ch)
+                        .data('annotation', annotation)
+                        .appendTo(element);
+                }
             });
             plugin.filters = {'text': testFilter};
             plugin.highlights = $(element).find('.annotator-hl');