scanning: Sort resolutions in resolution dropdown

Sort the resolutions in descending order and correctly select the
default option.

Bug: 1059779
Change-Id: If971e961b8174aec7d538cd21ca5ef0eada0f2c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2533395Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826571}

chrome/test/data/webui/chromeos/scanning/resolution_select_test.js

@@ -44,12 +44,12 @@ export function resolutionSelectTest() {
     assertFalse(select.disabled);
     assertEquals(2, select.length);
     assertEquals(
-        firstResolution.toString() + ' dpi',
+        secondResolution.toString() + ' dpi',
         select.options[0].textContent.trim());
     assertEquals(
-        secondResolution.toString() + ' dpi',
+        firstResolution.toString() + ' dpi',
         select.options[1].textContent.trim());
-    assertEquals(firstResolution.toString(), select.value);
+    assertEquals(secondResolution.toString(), select.value);
 
     // Selecting a different option should update the selected value.
     return changeSelect(
@@ -80,4 +80,27 @@ export function resolutionSelectTest() {
     assertEquals(2, select.length);
     assertFalse(select.disabled);
   });
+
+  test('resolutionsSortedCorrectly', () => {
+    resolutionSelect.resolutions = [150, 300, 75, 600, 1200, 200];
+    flush();
+
+    // Verify the resolutions are sorted in descending order and that 300 is
+    // selected by default.
+    for (let i = 0; i < resolutionSelect.resolutions.length - 1; i++) {
+      assert(
+          resolutionSelect.resolutions[i] >
+          resolutionSelect.resolutions[i + 1]);
+    }
+    assertEquals('300', resolutionSelect.selectedResolution);
+  });
+
+  test('firstResolutionUsedWhenDefaultNotAvailable', () => {
+    resolutionSelect.resolutions = [150, 75, 600, 1200, 200];
+    flush();
+
+    // Verify the first resolution in the sorted resolution array is selected by
+    // default when 300 is not an available option.
+    assertEquals('1200', resolutionSelect.selectedResolution);
+  });
 }

chromeos/components/scanning/resources/resolution_select.html

@@ -8,7 +8,8 @@
         disabled="[[disabled]]">
       <!-- TODO(jschettler): Sort the resolutions. -->
       <template is="dom-repeat" items="[[resolutions]]" as="resolution">
-        <option value="[[resolution]]">
+        <option value="[[resolution]]"
+            selected$="[[isDefaultResolution_(resolution)]]">
           [[getResolutionString_(resolution)]]
         </option>
       </template>

chromeos/components/scanning/resources/resolution_select.js

@@ -12,6 +12,9 @@ import {html, Polymer} from 'chrome://resources/polymer/v3_0/polymer/polymer_bun
 
 import {SelectBehavior} from './select_behavior.js';
 
+/** @type {number} */
+const DEFAULT_RESOLUTION = 300;
+
 /**
  * @fileoverview
  * 'resolution-select' displays the available scan resolutions in a dropdown.
@@ -37,7 +40,10 @@ Polymer({
     },
   },
 
-  observers: ['onNumOptionsChange(resolutions.length)'],
+  observers: [
+    'onNumOptionsChange(resolutions.length)',
+    'onResolutionsChange_(resolutions.*)'
+  ],
 
   /**
    * @param {number} resolution
@@ -48,4 +54,47 @@ Polymer({
     return loadTimeData.getStringF(
         'resolutionOptionText', resolution.toString());
   },
+
+  /**
+   * 300 dpi should be the default option if it exists. If not, use the first
+   * resolution in the resolutions array.
+   * @return {string}
+   * @private
+   */
+  getDefaultSelectedResolution_() {
+    const defaultResolutionIndex = this.resolutions.findIndex((resolution) => {
+      return this.isDefaultResolution_(resolution);
+    });
+
+    return defaultResolutionIndex === -1 ?
+        this.resolutions[0].toString() :
+        this.resolutions[defaultResolutionIndex].toString();
+  },
+
+  /**
+   * Sorts the resolutions and sets the selected resolution when the resolutions
+   * array changes.
+   * @private
+   */
+  onResolutionsChange_() {
+    if (this.resolutions.length > 1) {
+      // Sort the resolutions in descending order.
+      this.resolutions.sort(function(a, b) {
+        return b - a;
+      });
+    }
+
+    if (this.resolutions.length > 0) {
+      this.selectedResolution = this.getDefaultSelectedResolution_();
+    }
+  },
+
+  /**
+   * @param {number} resolution
+   * @return {boolean}
+   * @private
+   */
+  isDefaultResolution_(resolution) {
+    return resolution === DEFAULT_RESOLUTION;
+  },
 });

chromeos/components/scanning/resources/scanning_app.js

@@ -232,7 +232,6 @@ Polymer({
     this.selectedColorMode = this.capabilities_.colorModes[0].toString();
     this.selectedPageSize =
         this.capabilities_.sources[0].pageSizes[0].toString();
-    this.selectedResolution = this.capabilities_.resolutions[0].toString();
 
     // TODO(jschettler): Change default file type back to PDF when it's
     // supported.