Improve navigator by splitting it into 2 separate

.changeset/late-donuts-call.md

@@ -0,0 +1,10 @@
+---
+"@tma.js/navigation": patch
+---
+
+Divide `Navigator` into 2 separate:
+
+1. `BasicNavigator` which encapsulates logic related to any type of navigation.
+2. `HashNavigator` which is based on `BasicNavigator` and allows client routing via `window.location.history` and location hash.
+
+This engagement allows developers to implement some other routers. For example, it allows creating `MemoryNavigator` or bind to the Next router.

packages/navigation/src/BasicNavigator.ts

@@ -0,0 +1,199 @@
+import { EventEmitter } from '@tma.js/event-emitter';
+
+import type {
+  NavigationEntry,
+  NavigatorEventsMap,
+  AllowedEntry,
+} from './types.js';
+
+/**
+ * Represents a navigator which can be used in Telegram Mini Apps providing stable routing.
+ */
+export class BasicNavigator {
+  private readonly ee = new EventEmitter<NavigatorEventsMap>();
+
+  constructor(
+    private entries: NavigationEntry[],
+    private entriesCursor: number,
+  ) {
+    if (entries.length === 0) {
+      throw new Error('Entries should not be empty');
+    }
+
+    if (entriesCursor >= entries.length) {
+      throw new Error('Cursor should be less than or equal to entries count');
+    }
+  }
+
+  /**
+   * Converts externally specified entry data to the full entry.
+   * @param entry - entry data
+   */
+  private formatAllowedEntry(entry: AllowedEntry): NavigationEntry {
+    let url: URL;
+    const absolutePath = `https://localhost${this.path}`;
+
+    if (typeof entry === 'string') {
+      url = new URL(entry, absolutePath);
+    } else {
+      const { pathname = '', search = '' } = entry;
+      url = new URL(`${pathname}${search.startsWith('?') ? '' : '?'}${search}`);
+    }
+
+    return {
+      pathname: url.pathname,
+      search: url.search,
+    };
+  }
+
+  /**
+   * Emits "change" event with current navigator data.
+   */
+  private emitChange() {
+    this.ee.emit('change', {
+      pathname: this.pathname,
+      search: this.search,
+    });
+  }
+
+  /**
+   * Returns current entries cursor.
+   */
+  get cursor(): number {
+    return this.entriesCursor;
+  }
+
+  /**
+   * Returns true in case, navigator can go back.
+   */
+  canGoBack(): boolean {
+    return this.entriesCursor > 0;
+  }
+
+  /**
+   * Returns true in case, navigator can go forward.
+   */
+  canGoForward(): boolean {
+    return this.entriesCursor !== this.entries.length - 1;
+  }
+
+  /**
+   * Moves cursor by specified delta.
+   * @param delta - cursor delta.
+   * @returns True if changes were done.
+   */
+  go(delta: number): boolean {
+    // Cursor should be in bounds: [0, this.entries).
+    const cursor = Math.min(
+      this.entries.length - 1,
+      Math.max(this.entriesCursor + delta, 0),
+    );
+
+    if (this.entriesCursor === cursor) {
+      return false;
+    }
+
+    this.entriesCursor = cursor;
+    this.emitChange();
+
+    return true;
+  }
+
+  /**
+   * Returns readonly version of current entries.
+   */
+  getEntries(): readonly Readonly<NavigationEntry>[] {
+    return this.entries.map((item) => Object.freeze(item));
+  }
+
+  /**
+   * Adds new event listener.
+   */
+  on = this.ee.on.bind(this.ee);
+
+  /**
+   * Removes event listener.
+   */
+  off = this.ee.off.bind(this.ee);
+
+  /**
+   * Pushes new entry. It removes all entries after the current one and inserts new one.
+   * @param entry - entry data.
+   *
+   * @example Pushing absolute pathname.
+   * push("/absolute-path"); // "/absolute-path"
+   *
+   * @example Pushing relative pathname.
+   * // Pushing relative path replaces N last path parts, where N is pushed pathname parts count.
+   * // Pushing empty path is recognized as relative, but not replacing the last pathname part.
+   * push("relative"); // "/home/root" -> "/home/relative"
+   *
+   * @example Pushing query parameters.
+   * push("/absolute?my-param=1"); // "/home" -> "/absolute?my-param=1"
+   * push("relative?my-param=1"); // "/home/root" -> "/home/relative?my-param=1"
+   * push("?my-param=1"); // "/home" -> "/home?my-param=1"
+   */
+  push(entry: AllowedEntry): void {
+    // In case, current cursor refers not to the last one element in the history, we should
+    // remove everything after the cursor.
+    if (this.entriesCursor !== this.entries.length - 1) {
+      this.entries = this.entries.slice(0, this.entriesCursor + 1);
+    }
+
+    const formatted = this.formatAllowedEntry(entry);
+    this.entriesCursor += 1;
+    this.entries[this.entriesCursor] = formatted;
+    this.emitChange();
+  }
+
+  /**
+   * Returns current full path including pathname and query parameters.
+   */
+  get path(): string {
+    return `${this.pathname}${this.search}`;
+  }
+
+  /**
+   * Returns current pathname.
+   *
+   * @example Always returned value.
+   * "/abc"
+   */
+  get pathname(): string {
+    return this.entries[this.entriesCursor].pathname;
+  }
+
+  /**
+   * Replaces current entry. Has the same logic as "push" method does.
+   * @param entry - entry data.
+   * @see push
+   * @returns True if changes were done.
+   */
+  replace(entry: AllowedEntry): boolean {
+    const item = this.formatAllowedEntry(entry);
+    if (this.search === item.search && this.pathname === item.pathname) {
+      return false;
+    }
+
+    this.entries[this.entriesCursor] = item;
+    this.emitChange();
+
+    return true;
+  }
+
+  /**
+   * Returns current query parameters.
+   *
+   * @example Empty parameters.
+   * ""
+   *
+   * @example Empty parameters but with question mark.
+   * "?"
+   *
+   * @example Parameters list.
+   * "?param=1"
+   */
+  get search(): string {
+    return this.entries[this.entriesCursor].search;
+  }
+}