From 6120835f023cf6349fbbee21768894d3fa9ea7c9 Mon Sep 17 00:00:00 2001
From: Lars Gyrup Brink Nielsen <larsbrinknielsen@gmail.com>
Date: Tue, 23 May 2023 01:29:02 +0200
Subject: [PATCH] feat: add WIP `RouterHistoryStore#nextUrl$` property

---
 .../router-history.store.spec.ts              | 70 ++++++++++++++++++-
 .../router-history.store.ts                   | 32 +++++++++
 2 files changed, 99 insertions(+), 3 deletions(-)

diff --git a/packages/router-component-store/src/lib/router-history-store/router-history.store.spec.ts b/packages/router-component-store/src/lib/router-history-store/router-history.store.spec.ts
index cd4d8d1..a46f4da 100644
--- a/packages/router-component-store/src/lib/router-history-store/router-history.store.spec.ts
+++ b/packages/router-component-store/src/lib/router-history-store/router-history.store.spec.ts
@@ -30,6 +30,14 @@ function createTestComponent(name: string, selector: string) {
       >&lt; Back</a
     >
 
+    <a
+      id="forward-link"
+      *ngIf="routerHistory.nextUrl$ | async as nextUrl"
+      [href]="nextUrl"
+      (click)="onNext($event)"
+      >&gt; Next</a
+    >
+
     <a id="home-link" routerLink="/">Home</a>
     <a id="about-link" routerLink="about">About</a>
     <a id="company-link" routerLink="company">Company</a>
@@ -45,6 +53,11 @@ class TestAppComponent {
     event.preventDefault();
     this.routerHistory.onNavigateBack();
   }
+
+  onNext(event: MouseEvent) {
+    event.preventDefault();
+    this.routerHistory.onNavigateForward();
+  }
 }
 
 describe(RouterHistoryStore.name, () => {
@@ -98,7 +111,7 @@ describe(RouterHistoryStore.name, () => {
   }
 
   it('the URLs behave like the History API when navigating using links', async () => {
-    expect.assertions(2);
+    expect.assertions(3);
 
     const { click, routerHistory } = await setup();
 
@@ -112,10 +125,11 @@ describe(RouterHistoryStore.name, () => {
 
     expect(await firstValueFrom(routerHistory.currentUrl$)).toBe('/products');
     expect(await firstValueFrom(routerHistory.previousUrl$)).toBe('/company');
+    expect(await firstValueFrom(routerHistory.nextUrl$)).toBe(undefined);
   });
 
   it('the URLs behave like the History API when navigating back', async () => {
-    expect.assertions(2);
+    expect.assertions(3);
 
     const { click, routerHistory } = await setup();
 
@@ -129,10 +143,31 @@ describe(RouterHistoryStore.name, () => {
 
     expect(await firstValueFrom(routerHistory.currentUrl$)).toBe('/about');
     expect(await firstValueFrom(routerHistory.previousUrl$)).toBe('/home');
+    expect(await firstValueFrom(routerHistory.nextUrl$)).toBe('/company');
+  });
+
+  it('the URLs behave like the History API when navigating back twice', async () => {
+    expect.assertions(3);
+
+    const { click, routerHistory } = await setup();
+
+    // At Home
+    await click('#about-link');
+    // At About
+    await click('#company-link');
+    // At Company
+    await click('#back-link');
+    // At About
+    await click('#back-link');
+    // At Home
+
+    expect(await firstValueFrom(routerHistory.currentUrl$)).toBe('/home');
+    expect(await firstValueFrom(routerHistory.previousUrl$)).toBe(undefined);
+    expect(await firstValueFrom(routerHistory.nextUrl$)).toBe('/about');
   });
 
   it('the URLs behave like the History API when navigating back then using links', async () => {
-    expect.assertions(2);
+    expect.assertions(3);
 
     const { click, routerHistory } = await setup();
 
@@ -148,5 +183,34 @@ describe(RouterHistoryStore.name, () => {
 
     expect(await firstValueFrom(routerHistory.currentUrl$)).toBe('/products');
     expect(await firstValueFrom(routerHistory.previousUrl$)).toBe('/about');
+    expect(await firstValueFrom(routerHistory.nextUrl$)).toBe(undefined);
+  });
+
+  it('the URLs behave like the History API when navigating back then forward', async () => {
+    expect.assertions(3);
+
+    const { click, routerHistory } = await setup();
+
+    // At Home
+    await click('#about-link');
+    // At About
+    // Previous: Home
+    // Next: None
+    await click('#company-link');
+    // At Company
+    // Previous: About
+    // Next: None
+    await click('#back-link');
+    // At About
+    // Previous: Home
+    // Next: Company
+    await click('#forward-link');
+    // At Company
+    // Previous: About
+    // Next: None
+
+    expect(await firstValueFrom(routerHistory.currentUrl$)).toBe('/company');
+    expect(await firstValueFrom(routerHistory.previousUrl$)).toBe('/about');
+    expect(await firstValueFrom(routerHistory.nextUrl$)).toBe(undefined);
   });
 });
diff --git a/packages/router-component-store/src/lib/router-history-store/router-history.store.ts b/packages/router-component-store/src/lib/router-history-store/router-history.store.ts
index b161743..ee09b15 100644
--- a/packages/router-component-store/src/lib/router-history-store/router-history.store.ts
+++ b/packages/router-component-store/src/lib/router-history-store/router-history.store.ts
@@ -127,6 +127,38 @@ export class RouterHistoryStore extends ComponentStore<RouterHistoryState> {
     this.#latestRouterNavigatedSequence$,
     ([, navigationEnd]) => navigationEnd.urlAfterRedirects
   );
+  /**
+   * The next URL when taking `popstate` events into account.
+   *
+   * `undefined` is emitted when the current navigation is the last in the
+   * navigation history.
+   */
+  nextUrl$: Observable<string | undefined> = this.select(
+    this.#history$,
+    this.#maxNavigatedId$,
+    (history, maxNavigatedId) => {
+      if (maxNavigatedId === 1) {
+        return undefined;
+      }
+
+      const [sourceNavigationStart] = this.#findSourceNavigatedSequence(
+        maxNavigatedId,
+        history
+      );
+
+      if (sourceNavigationStart.id === maxNavigatedId) {
+        return undefined;
+      }
+
+      const nextNavigationId = sourceNavigationStart.id + 1;
+      const [, nextNavigationEnd] = this.#findSourceNavigatedSequence(
+        nextNavigationId,
+        history
+      );
+
+      return nextNavigationEnd.urlAfterRedirects;
+    }
+  );
   /**
    * The previous URL when taking `popstate` events into account.
    *