refactor: move memoize function to shared utils (#2090)

We move the memoize function to `lib/shared/utils.js` and expose it to
modules across the project.

Change-Type: patch
Changelog-Entry: Move memoize function to shared utils.

lib/gui/app/components/drive-selector/controllers/drive-selector.js

@@ -23,6 +23,7 @@ const constraints = require('../../../../../shared/drive-constraints')
 const analytics = require('../../../modules/analytics')
 const availableDrives = require('../../../../../shared/models/available-drives')
 const selectionState = require('../../../../../shared/models/selection-state')
+const utils = require('../../../../../shared/utils')
 
 module.exports = function (
   $q,
@@ -173,66 +174,17 @@ module.exports = function (
   }
 
   /**
-   * @summary Memoize ImmutableJS list reference
+   * @summary Memoized getDrives function
    * @function
-   * @private
+   * @public
    *
-   * @description
-   * This workaround is needed to avoid AngularJS from getting
-   * caught in an infinite digest loop when using `ngRepeat`
-   * over a function that returns a mutable version of an
-   * ImmutableJS object.
-   *
-   * The problem is that every time you call `myImmutableObject.toJS()`
-   * you will get a new object, whose reference is different from
-   * the one you previously got, even if the data is exactly the same.
-   *
-   * @param {Function} func - function that returns an ImmutableJS list
-   * @returns {Function} memoized function
+   * @returns {Array<Object>} - memoized list of drives
    *
    * @example
-   * const getList = () => {
-   *   return Store.getState().toJS().myList;
-   * };
-   *
-   * const memoizedFunction = memoizeImmutableListReference(getList);
+   * const drives = DriveSelectorController.getDrives()
+   * // Do something with drives
    */
-  this.memoizeImmutableListReference = (func) => {
-    let previousTuples = []
-
-    return (...restArgs) => {
-      let areArgsInTuple = false
-      let state = Reflect.apply(func, this, restArgs)
-
-      previousTuples = _.map(previousTuples, ([ oldArgs, oldState ]) => {
-        if (angular.equals(oldArgs, restArgs)) {
-          areArgsInTuple = true
-
-          if (angular.equals(state, oldState)) {
-            // Use the previously memoized state for this argument
-            state = oldState
-          }
-
-          // Update the tuple state
-          return [ oldArgs, state ]
-        }
-
-        // Return the tuple unchanged
-        return [ oldArgs, oldState ]
-      })
-
-      // Add the state associated with these args to be memoized
-      if (!areArgsInTuple) {
-        previousTuples.push([ restArgs, state ])
-      }
-
-      return state
-    }
-  }
-
-  this.getDrives = this.memoizeImmutableListReference(() => {
-    return this.drives.getDrives()
-  })
+  this.getDrives = utils.memoize(this.drives.getDrives, angular.equals)
 
   /**
    * @summary Get a drive's compatibility status object(s)
@@ -253,9 +205,9 @@ module.exports = function (
    *   // do something
    * }
    */
-  this.getDriveStatuses = this.memoizeImmutableListReference((drive) => {
+  this.getDriveStatuses = utils.memoize((drive) => {
     return this.constraints.getDriveImageCompatibilityStatuses(drive, this.state.getImage())
-  })
+  }, angular.equals)
 
   /**
    * @summary Keyboard event drive toggling

lib/shared/utils.js

@@ -78,3 +78,62 @@ exports.percentageToFloat = (percentage) => {
 
   return percentage / exports.PERCENTAGE_MAXIMUM
 }
+
+/**
+ * @summary Memoize a function
+ * @function
+ * @private
+ *
+ * @description
+ * This workaround is needed to avoid AngularJS from getting
+ * caught in an infinite digest loop when using `ngRepeat`
+ * over a function that returns a mutable version of an
+ * ImmutableJS object.
+ *
+ * The problem is that every time you call `myImmutableObject.toJS()`
+ * you will get a new object, whose reference is different from
+ * the one you previously got, even if the data is exactly the same.
+ *
+ * @param {Function} func - function that returns an ImmutableJS list
+ * @param {Function} comparer - function to compare old and new args and state
+ * @returns {Function} memoized function
+ *
+ * @example
+ * const getList = () => {
+ *   return Store.getState().toJS().myList;
+ * };
+ *
+ * const memoizedFunction = memoize(getList, angular.equals);
+ */
+exports.memoize = (func, comparer) => {
+  let previousTuples = []
+
+  return (...restArgs) => {
+    let areArgsInTuple = false
+    let state = Reflect.apply(func, this, restArgs)
+
+    previousTuples = _.map(previousTuples, ([ oldArgs, oldState ]) => {
+      if (comparer(oldArgs, restArgs)) {
+        areArgsInTuple = true
+
+        if (comparer(state, oldState)) {
+          // Use the previously memoized state for this argument
+          state = oldState
+        }
+
+        // Update the tuple state
+        return [ oldArgs, state ]
+      }
+
+      // Return the tuple unchanged
+      return [ oldArgs, oldState ]
+    })
+
+    // Add the state associated with these args to be memoized
+    if (!areArgsInTuple) {
+      previousTuples.push([ restArgs, state ])
+    }
+
+    return state
+  }
+}

tests/gui/components/drive-selector.spec.js

@@ -20,6 +20,7 @@ const _ = require('lodash')
 const m = require('mochainon')
 const angular = require('angular')
 require('angular-mocks')
+const utils = require('../../../lib/shared/utils')
 
 describe('Browser: DriveSelector', function () {
   beforeEach(angular.mock.module(
@@ -27,64 +28,9 @@ describe('Browser: DriveSelector', function () {
   ))
 
   describe('DriveSelectorController', function () {
-    let $controller
-    let $rootScope
-    let $q
-    let $uibModalInstance
-    let WarningModalService
-
-    let controller
-
-    beforeEach(angular.mock.inject(function (
-      _$controller_,
-      _$rootScope_,
-      _$q_,
-      _WarningModalService_
-    ) {
-      $controller = _$controller_
-      $rootScope = _$rootScope_
-      $q = _$q_
-      $uibModalInstance = {}
-      WarningModalService = _WarningModalService_
-    }))
-
-    beforeEach(() => {
-      controller = $controller('DriveSelectorController', {
-        $scope: $rootScope.$new(),
-        $q,
-        $uibModalInstance,
-        WarningModalService
-      })
-    })
-
-    describe('.memoizeImmutableListReference()', function () {
-      it('constant true should return memoized true', function () {
-        const memoizedConstTrue = controller.memoizeImmutableListReference(_.constant(true))
-        m.chai.expect(memoizedConstTrue()).to.be.true
-      })
-
-      it('should reflect state changes', function () {
-        let stateA = false
-        const memoizedStateA = controller.memoizeImmutableListReference(() => {
-          return stateA
-        })
-
-        m.chai.expect(memoizedStateA()).to.be.false
-
-        stateA = true
-
-        m.chai.expect(memoizedStateA()).to.be.true
-      })
-
-      it('should reflect different arguments', function () {
-        const memoizedParameter = controller.memoizeImmutableListReference(_.identity)
-
-        m.chai.expect(memoizedParameter(false)).to.be.false
-        m.chai.expect(memoizedParameter(true)).to.be.true
-      })
-
+    describe('.memoize()', function () {
       it('should handle equal angular objects with different hashes', function () {
-        const memoizedParameter = controller.memoizeImmutableListReference(_.identity)
+        const memoizedParameter = utils.memoize(_.identity, angular.equals)
         const angularObjectA = {
           $$hashKey: 1,
           keyA: true

tests/shared/utils.spec.js

@@ -16,6 +16,7 @@
 
 'use strict'
 
+const _ = require('lodash')
 const m = require('mochainon')
 const utils = require('../../lib/shared/utils')
 
@@ -125,4 +126,31 @@ describe('Shared: Utils', function () {
       }).to.throw('Invalid percentage: 100.01')
     })
   })
+
+  describe('.memoize()', function () {
+    it('constant true should return memoized true', function () {
+      const memoizedConstTrue = utils.memoize(_.constant(true), _.isEqual)
+      m.chai.expect(memoizedConstTrue()).to.be.true
+    })
+
+    it('should reflect state changes', function () {
+      let stateA = false
+      const memoizedStateA = utils.memoize(() => {
+        return stateA
+      }, _.isEqual)
+
+      m.chai.expect(memoizedStateA()).to.be.false
+
+      stateA = true
+
+      m.chai.expect(memoizedStateA()).to.be.true
+    })
+
+    it('should reflect different arguments', function () {
+      const memoizedParameter = utils.memoize(_.identity, _.isEqual)
+
+      m.chai.expect(memoizedParameter(false)).to.be.false
+      m.chai.expect(memoizedParameter(true)).to.be.true
+    })
+  })
 })