added services and interfaces for expense types

src/app/services/http.ts

@@ -0,0 +1,40 @@
+import { Injectable } from '@angular/core';
+import { HttpClient } from '@angular/common/http';
+import { firstValueFrom } from 'rxjs';
+
+@Injectable({
+  providedIn: 'root',
+})
+export class Http {
+  public constructor(private httpClient: HttpClient) { }
+
+  public async get<T>(url: string): Promise<T> {
+    return this.request<T>(url, 'get');
+  }
+
+  public async post<T>(url: string, body?: any): Promise<T> {
+    return this.request<T>(url, 'post', body);
+  }
+
+  public async put<T>(url: string, body?: any): Promise<T> {
+    return this.request<T>(url, 'put', body);
+  }
+
+  public async delete<T>(url: string): Promise<T> {
+    return this.request<T>(url, 'delete');
+  }
+
+  private async request<T>(url: string, method: 'get' | 'post' | 'put' | 'delete', body?: any): Promise<T> {
+    const headers = { 'Accept': 'application/json', 'Content-Type': 'application/json' };
+    switch (method) {
+      case 'post':
+        return firstValueFrom(this.httpClient.post<T>(url, body, { headers }));
+      case 'put':
+        return firstValueFrom(this.httpClient.put<T>(url, body, { headers }));
+      case 'delete':
+        return firstValueFrom(this.httpClient.delete<T>(url, { headers }));
+      default:
+        return firstValueFrom(this.httpClient.get<T>(url, { headers }));
+    }
+  }
+}