feat: add RouterHistoryStore

packages/router-component-store/src/lib/router-history-store/router-history.store.ts

@@ -0,0 +1,177 @@
+import { inject, Injectable, Provider } from '@angular/core';
+import {
+  Navigation,
+  NavigationEnd,
+  NavigationStart,
+  Router,
+} from '@angular/router';
+import { ComponentStore, provideComponentStore } from '@ngrx/component-store';
+import { concatMap, filter, Observable, take } from 'rxjs';
+
+interface RouterHistoryRecord {
+  readonly id: number;
+  readonly url: string;
+}
+
+interface RouterHistoryState {
+  readonly currentIndex: number;
+  readonly event: NavigationStart | NavigationEnd | null;
+  readonly history: readonly RouterHistoryRecord[];
+  readonly id: number;
+  readonly idToRestore?: number;
+  readonly trigger?: Navigation['trigger'];
+}
+
+export function provideRouterHistoryStore(): Provider[] {
+  return [provideComponentStore(RouterHistoryStore)];
+}
+
+@Injectable()
+export class RouterHistoryStore extends ComponentStore<RouterHistoryState> {
+  #router = inject(Router);
+
+  #currentIndex$: Observable<number> = this.select(
+    (state) => state.currentIndex
+  );
+  #history$: Observable<readonly RouterHistoryRecord[]> = this.select(
+    (state) => state.history
+  );
+  #navigationEnd$: Observable<NavigationEnd> = this.#router.events.pipe(
+    filter((event): event is NavigationEnd => event instanceof NavigationEnd)
+  );
+  #navigationStart$: Observable<NavigationStart> = this.#router.events.pipe(
+    filter(
+      (event): event is NavigationStart => event instanceof NavigationStart
+    )
+  );
+  #imperativeNavigationEnd$: Observable<NavigationEnd> =
+    this.#navigationStart$.pipe(
+      filter((event) => event.navigationTrigger === 'imperative'),
+      concatMap(() => this.#navigationEnd$.pipe(take(1)))
+    );
+  #popstateNavigationEnd$: Observable<NavigationEnd> =
+    this.#navigationStart$.pipe(
+      filter((event) => event.navigationTrigger === 'popstate'),
+      concatMap(() => this.#navigationEnd$.pipe(take(1)))
+    );
+
+  currentUrl$: Observable<string> = this.select(
+    this.#navigationEnd$.pipe(
+      concatMap(() =>
+        this.select(
+          this.#currentIndex$,
+          this.#history$,
+          (currentIndex, history) => [currentIndex, history] as const
+        )
+      )
+    ),
+    ([currentIndex, history]) => history[currentIndex].url
+  );
+  previousUrl$: Observable<string | null> = this.select(
+    this.#navigationEnd$.pipe(
+      concatMap(() =>
+        this.select(
+          this.#currentIndex$,
+          this.#history$,
+          (currentIndex, history) => [currentIndex, history] as const
+        )
+      )
+    ),
+    ([currentIndex, history]) => history[currentIndex - 1]?.url ?? null
+  );
+
+  constructor() {
+    super(initialState);
+
+    this.#updateRouterHistoryOnNavigationStart(this.#navigationStart$);
+    this.#updateRouterHistoryOnImperativeNavigationEnd(
+      this.#imperativeNavigationEnd$
+    );
+    this.#updateRouterHistoryOnPopstateNavigationEnd(
+      this.#popstateNavigationEnd$
+    );
+  }
+
+  /**
+   * Update router history on imperative navigation end (`Router#navigate`,
+   * `Router#navigateByUrl`, or `RouterLink`).
+   */
+  #updateRouterHistoryOnImperativeNavigationEnd = this.updater<NavigationEnd>(
+    (state, event): RouterHistoryState => {
+      let currentIndex = state.currentIndex;
+      let history = state.history;
+      // remove all events in history that come after the current index
+      history = [
+        ...history.slice(0, currentIndex),
+        // add the new event to the end of the history
+        {
+          id: state.id,
+          url: event.urlAfterRedirects,
+        },
+      ];
+      // set the new event as our current history index
+      currentIndex = history.length - 1;
+
+      return {
+        ...state,
+        currentIndex,
+        event,
+        history,
+      };
+    }
+  );
+
+  #updateRouterHistoryOnNavigationStart = this.updater<NavigationStart>(
+    (state, event): RouterHistoryState => ({
+      ...state,
+      id: event.id,
+      idToRestore: event.restoredState?.navigationId ?? undefined,
+      event,
+      trigger: event.navigationTrigger,
+    })
+  );
+
+  /**
+   * Update router history on browser navigation end (back, forward, and other
+   * `popstate` events).
+   */
+  #updateRouterHistoryOnPopstateNavigationEnd = this.updater<NavigationEnd>(
+    (state, event): RouterHistoryState => {
+      let currentIndex = 0;
+      let { history } = state;
+      // get the history item that references the idToRestore
+      const historyIndexToRestore = history.findIndex(
+        (historyRecord) => historyRecord.id === state.idToRestore
+      );
+
+      // if found, set the current index to that history item and update the id
+      if (historyIndexToRestore > -1) {
+        currentIndex = historyIndexToRestore;
+        history = [
+          ...history.slice(0, historyIndexToRestore),
+          {
+            ...history[historyIndexToRestore],
+            id: state.id,
+          },
+          ...history.slice(historyIndexToRestore + 1),
+        ];
+      }
+
+      return {
+        ...state,
+        currentIndex,
+        event,
+        history,
+      };
+    }
+  );
+}
+
+export const initialState: RouterHistoryState = {
+  currentIndex: 0,
+  event: null,
+  history: [],
+  id: 0,
+  idToRestore: 0,
+  trigger: undefined,
+};