Review update 1

Author: kurkle

src/core/core.controller.js

@@ -396,13 +396,17 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 	},
 
 	/**
+	 * Updates the given metaset with the given dataset index. Ensures it's stored at that index
+	 * in the _metasets array by swapping with the metaset at that index if necessary.
+	 * @param {Object} meta - the dataset metadata
+	 * @param {number} index - the dataset index
 	 * @private
 	 */
 	_updateMetasetIndex: function(meta, index) {
 		const metasets = this._metasets;
-		const old = meta.index;
-		if (old !== index) {
-			metasets[old] = metasets[index];
+		const oldIndex = meta.index;
+		if (oldIndex !== index) {
+			metasets[oldIndex] = metasets[index];
 			metasets[index] = meta;
 			meta.index = index;
 		}

test/specs/core.controller.tests.js

@@ -1325,4 +1325,75 @@ describe('Chart', function() {
 			);
 		});
 	});
+
+	describe('metasets', function() {
+		beforeEach(function() {
+			this.chart = acquireChart({
+				type: 'line',
+				data: {
+					datasets: [
+						{label: '1', order: 2},
+						{label: '2', order: 1},
+						{label: '3', order: 4},
+						{label: '4', order: 3},
+					]
+				}
+			});
+		});
+		afterEach(function() {
+			const metasets = this.chart._metasets;
+			expect(metasets.length).toEqual(this.chart.data.datasets.length);
+			for (let i = 0; i < metasets.length; i++) {
+				expect(metasets[i].index).toEqual(i);
+				expect(metasets[i]._dataset).toEqual(this.chart.data.datasets[i]);
+			}
+		});
+		it('should build metasets array in order', function() {
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(1);
+			expect(metasets[2].order).toEqual(4);
+			expect(metasets[3].order).toEqual(3);
+		});
+		it('should build sorted metasets array in correct order', function() {
+			const metasets = this.chart._sortedMetasets;
+			expect(metasets[0].order).toEqual(1);
+			expect(metasets[1].order).toEqual(2);
+			expect(metasets[2].order).toEqual(3);
+			expect(metasets[3].order).toEqual(4);
+		});
+		it('should be moved when datasets are removed from begining', function() {
+			this.chart.data.datasets.splice(0, 2);
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(4);
+			expect(metasets[1].order).toEqual(3);
+		});
+		it('should be moved when datasets are removed from middle', function() {
+			this.chart.data.datasets.splice(1, 2);
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(3);
+		});
+		it('should be moved when datasets are inserted', function() {
+			this.chart.data.datasets.splice(1, 0, {label: '1.5', order: 5});
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(5);
+			expect(metasets[2].order).toEqual(1);
+			expect(metasets[3].order).toEqual(4);
+			expect(metasets[4].order).toEqual(3);
+		});
+		it('should be replaced when dataset is replaced', function() {
+			this.chart.data.datasets.splice(1, 1, {label: '1.5', order: 5});
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(5);
+			expect(metasets[2].order).toEqual(4);
+			expect(metasets[3].order).toEqual(3);
+		});
+	});
 });