Refactoring an Angular Component for Improved Readability and Testability

This challenge focuses on refactoring an existing Angular component to improve its readability, maintainability, and testability. You'll be given a component with some common code smells – long methods, tightly coupled logic, and difficulty in unit testing. Your task is to apply appropriate refactoring techniques to address these issues, resulting in a cleaner, more robust component.

Problem Description

You are provided with an Angular component (ProductListComponent) that displays a list of products fetched from a service. The component currently has a single, long method (loadProducts) that handles fetching data, filtering, and formatting. This method is difficult to read, understand, and test. Your goal is to refactor this component to:

1. Extract Logic into Smaller, Reusable Functions: Break down the loadProducts method into smaller, well-named functions, each responsible for a specific task (e.g., fetching data, filtering products, formatting product data).
2. Improve Testability: Make the component easier to unit test by isolating dependencies and reducing the complexity of the component's logic. Specifically, you should aim to mock the product service easily.
3. Enhance Readability: Improve the overall readability of the component's code by using clear variable names, consistent formatting, and appropriate comments where necessary.
4. Consider Observables: The component uses Observables for data fetching. Ensure your refactoring doesn't negatively impact the observable handling.

Expected Behavior:

The refactored component should maintain the same functionality as the original component: it should fetch a list of products, filter them based on a search term (if provided), and display the filtered list. The component's template should remain unchanged. The refactored code should be more readable, maintainable, and easier to test.

Edge Cases to Consider:

• Empty Product List: Handle the case where the product list is empty gracefully.
• Error Handling: The original component has basic error handling. Ensure your refactoring preserves this functionality.
• Search Term: The component filters products based on a search term. Ensure this filtering logic is correctly refactored.

Examples

Example 1:

Input: Original ProductListComponent (see provided code below)
Output: Refactored ProductListComponent with smaller functions, improved testability, and enhanced readability.
Explanation: The `loadProducts` method is broken down into `fetchProducts`, `filterProducts`, and `formatProducts`. The product service is now easily mockable in unit tests.

Example 2:

Input: ProductListComponent with an empty product list.
Output: The component displays a message indicating that no products are available.
Explanation: The component correctly handles the edge case of an empty product list.

Constraints

• Angular Version: Assume Angular version 15 or later.
• TypeScript: The code must be written in TypeScript.
• No External Libraries: You are not allowed to use any external libraries beyond those typically included in an Angular project (e.g., RxJS).
• Template Unchanged: The component's HTML template should remain identical to the original.
• Functional Equivalence: The refactored component must produce the same output as the original component for the same input.

Notes

• Focus on applying refactoring principles rather than introducing new features.
• Consider using techniques like extracting methods, dependency injection, and functional programming to improve the code.
• Think about how your refactoring will impact the component's testability. Write unit tests to verify the correctness of your refactored code (though writing the tests themselves is not part of this challenge - the goal is to make them possible).
• The provided code contains some deliberate code smells to guide your refactoring efforts.

Original ProductListComponent Code (to be refactored):

import { Component, OnInit } from '@angular/core';
import { ProductService } from '../product.service';

interface Product {
  id: number;
  name: string;
  description: string;
  price: number;
}

@Component({
  selector: 'app-product-list',
  templateUrl: './product-list.component.html',
  styleUrls: ['./product-list.component.css']
})
export class ProductListComponent implements OnInit {
  products: Product[] = [];
  searchTerm: string = '';
  loading: boolean = true;
  error: string = '';

  constructor(private productService: ProductService) {}

  ngOnInit(): void {
    this.loadProducts();
  }

  loadProducts(): void {
    this.loading = true;
    this.error = '';

    this.productService.getProducts()
      .subscribe({
        next: (data) => {
          this.products = data;
          this.loading = false;
        },
        error: (err) => {
          this.error = err.message;
          this.loading = false;
        }
      });
  }

  filterProducts(): void {
    if (this.searchTerm) {
      this.products = this.products.filter(product =>
        product.name.toLowerCase().includes(this.searchTerm.toLowerCase()) ||
        product.description.toLowerCase().includes(this.searchTerm.toLowerCase())
      );
    } else {
      this.loadProducts(); // Reload all products if no search term
    }
  }
}

product.service.ts (for context - do not modify):

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

interface Product {
  id: number;
  name: string;
  description: string;
  price: number;
}

@Injectable({
  providedIn: 'root'
})
export class ProductService {

  private apiUrl = 'https://fakestoreapi.com/products';

  constructor(private http: HttpClient) {}

  getProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(this.apiUrl);
  }
}

product-list.component.html (do not modify):

<div *ngIf="loading; else productsSection">
  <p>Loading products...</p>
</div>

<ng-template #productsSection>
  <div *ngIf="error; else productList">
    <p>{{ error }}</p>
  </div>

  <div *ngIf="productList; else noProducts">
    <input type="text" [(ngModel)]="searchTerm" (keyup.enter)="filterProducts()" placeholder="Search products...">
    <ul>
      <li *ngFor="let product of products">
        {{ product.name }} - ${{ product.price }}
      </li>
    </ul>
  </div>

  <div *ngIf="noProducts">
    <p>No products found.</p>
  </div>
</ng-template>