From 8e8f6e936ebabf68eee42eb212a2863ef1bda02d Mon Sep 17 00:00:00 2001
From: Andrea Carraro <me@andreacarraro.it>
Date: Sun, 9 Jun 2019 21:25:32 +0200
Subject: [PATCH] Add keySelectorCreator option

---
 README.md                                  | 17 +++++++
 src/__tests__/createCachedSelector.spec.js | 53 ++++++++++++++++------
 src/createCachedSelector.js                |  8 ++++
 src/index.d.ts                             | 30 ++++++++++--
 4 files changed, 88 insertions(+), 20 deletions(-)

diff --git a/README.md b/README.md
index 01e49e4e..10a82c67 100644
--- a/README.md
+++ b/README.md
@@ -386,6 +386,23 @@ Default: `reselect`'s [`createSelector`][reselect-create-selector]
 
 An optional function describing a [custom version of createSelector][reselect-create-selector-creator].
 
+#### keySelectorCreator
+
+Type: `function`<br />
+Default: `undefined`
+
+An optional function with the following signature returning the [`keySelector`](#keyselector) used by the cached selector.
+
+```typescript
+export type keySelectorCreator = (selectorInputs: {
+  inputSelectors: InputSelector[];
+  resultFunc: ResultFunc;
+  keySelector: KeySelector;
+}) => KeySelector;
+```
+
+This allows to dynamically **generate `keySelectors` on runtime** based on provided `inputSelectors`/`resultFunc` and support [**key selectors composition**](https://github.com/toomuchdesign/re-reselect/pull/73).
+
 ### re-reselect selector instance
 
 `createCachedSelector` and `createStructuredCachedSelector` return a **selector instance** which extends the API of a **standard reselect selector**.
diff --git a/src/__tests__/createCachedSelector.spec.js b/src/__tests__/createCachedSelector.spec.js
index 1b6f145b..01468848 100644
--- a/src/__tests__/createCachedSelector.spec.js
+++ b/src/__tests__/createCachedSelector.spec.js
@@ -114,24 +114,47 @@ describe('createCachedSelector', () => {
 
   it('Should throw an error when a function is provided as 2° argument', () => {
     expect(() => {
-      const cachedSelector = createCachedSelector(resultFuncMock)(() => {},
-      reselect.createSelector);
+      createCachedSelector(resultFuncMock)(() => {}, reselect.createSelector);
     }).toThrow(/Second argument "options" must be an object/);
   });
 
-  it('Should accept an options object', () => {
-    const cachedSelector = createCachedSelector(resultFuncMock)(
-      (arg1, arg2) => arg2,
-      {
-        cacheObject: new FlatObjectCache(),
-        selectorCreator: reselect.createSelector,
-      }
-    );
-
-    expect(cachedSelector.recomputations()).toBe(0);
-    cachedSelector('foo', 'bar');
-    cachedSelector('foo', 'bar');
-    expect(cachedSelector.recomputations()).toBe(1);
+  describe('options', () => {
+    it('Should accept cacheObject and selectorCreator options', () => {
+      const cachedSelector = createCachedSelector(resultFuncMock)(
+        (arg1, arg2) => arg2,
+        {
+          cacheObject: new FlatObjectCache(),
+          selectorCreator: reselect.createSelector,
+        }
+      );
+
+      expect(cachedSelector.recomputations()).toBe(0);
+      cachedSelector('foo', 'bar');
+      cachedSelector('foo', 'bar');
+      expect(cachedSelector.recomputations()).toBe(1);
+    });
+
+    it('Should accept selectorCreator option', () => {
+      const inputSelector = () => {};
+      const resultFunc = () => {};
+      const keySelector = () => {};
+      const generatedKeySelector = () => {};
+      const keySelectorCreatorMock = jest.fn(() => generatedKeySelector);
+
+      const cachedSelector = createCachedSelector(inputSelector, resultFunc)(
+        keySelector,
+        {
+          keySelectorCreator: keySelectorCreatorMock,
+        }
+      );
+
+      expect(keySelectorCreatorMock).toHaveBeenCalledWith({
+        inputSelectors: [inputSelector],
+        resultFunc: resultFunc,
+        keySelector: keySelector,
+      });
+      expect(cachedSelector.keySelector).toBe(generatedKeySelector);
+    });
   });
 
   describe('getMatchingSelector()', () => {
diff --git a/src/createCachedSelector.js b/src/createCachedSelector.js
index a566edc7..d598fdbb 100644
--- a/src/createCachedSelector.js
+++ b/src/createCachedSelector.js
@@ -28,6 +28,14 @@ function createCachedSelector(...funcs) {
     const selectorCreator = options.selectorCreator || createSelector;
     const isValidCacheKey = cache.isValidCacheKey || defaultCacheKeyValidator;
 
+    if (options.keySelectorCreator) {
+      keySelector = options.keySelectorCreator({
+        inputSelectors: dependencies,
+        resultFunc,
+        keySelector,
+      });
+    }
+
     // Application receives this function
     const selector = function(...args) {
       const cacheKey = keySelector(...args);
diff --git a/src/index.d.ts b/src/index.d.ts
index 38f79396..92689f12 100644
--- a/src/index.d.ts
+++ b/src/index.d.ts
@@ -34,20 +34,25 @@ export type OutputParametricSelector<S, P, R, C, D> = ParametricSelector<
 
 export type CreateSelectorInstance = typeof createSelector;
 
-type Options =
+type Options<S, C, D> =
   | {
       selectorCreator?: CreateSelectorInstance;
-      cacheObject: ICacheObject;
+      cacheObject?: ICacheObject;
+      keySelectorCreator?: KeySelectorCreator<S, C, D>;
     }
+  | CreateSelectorInstance;
+
+type ParametricOptions<S, P, C, D> =
   | {
-      selectorCreator: CreateSelectorInstance;
+      selectorCreator?: CreateSelectorInstance;
       cacheObject?: ICacheObject;
+      keySelectorCreator?: ParametricKeySelectorCreator<S, P, C, D>;
     }
   | CreateSelectorInstance;
 
 export type OutputCachedSelector<S, R, C, D> = (
   keySelector: KeySelector<S>,
-  optionsOrSelectorCreator?: Options
+  optionsOrSelectorCreator?: Options<S, C, D>
 ) => OutputSelector<S, R, C, D> & {
   getMatchingSelector: (state: S, ...args: any[]) => OutputSelector<S, R, C, D>;
   removeMatchingSelector: (state: S, ...args: any[]) => void;
@@ -58,7 +63,7 @@ export type OutputCachedSelector<S, R, C, D> = (
 
 export type OutputParametricCachedSelector<S, P, R, C, D> = (
   keySelector: ParametricKeySelector<S, P>,
-  optionsOrSelectorCreator?: Options
+  optionsOrSelectorCreator?: ParametricOptions<S, P, C, D>
 ) => OutputParametricSelector<S, P, R, C, D> & {
   getMatchingSelector: (
     state: S,
@@ -4447,3 +4452,18 @@ export class LruMapCache implements ICacheObject {
   remove(key: any): void;
   clear(): void;
 }
+
+/*
+ * Key selector creators
+ */
+export type KeySelectorCreator<S, C, D> = (selectorInputs: {
+  inputSelectors: D;
+  resultFunc: C;
+  keySelector: KeySelector<S>;
+}) => KeySelector<S>;
+
+export type ParametricKeySelectorCreator<S, P, C, D> = (selectorInputs: {
+  inputSelectors: D;
+  resultFunc: C;
+  keySelector: ParametricKeySelector<S, P>;
+}) => ParametricKeySelector<S, P>;