README.md

Composite Pattern

The Composite Pattern is like a container object, where the container can also have components, forming a recursive tree structure. Clients can handle it uniformly without distinguishing between components and containers.

It combines multiple objects to represent a hierarchical structure with a part-whole relationship. The Composite Pattern allows clients to treat individual objects and composite objects uniformly.

Therefore, the Composite Pattern consists of three roles: Abstract Component, Leaf Component, and Composite Component.

Now, let's develop antivirus software that scans folders and files, using different virus scanning methods for different file types.

1. Create an abstract file class, acting as an abstract component:

export abstract class AbstractFile {
  abstract add(file: AbstractFile): void;
  abstract remove(file: AbstractFile): void;
  abstract getChild(i: number): AbstractFile;
  abstract killVirus(): void;
}

2.1. Create an image file class, acting as a leaf component:

import { AbstractFile } from "./AbstractFile";

export class ImageFile extends AbstractFile {
  #name: string;
  constructor(name: string) {
    super();
    this.#name = name;
  }
  add(file: AbstractFile): void {
    console.log("Sorry, this method is not supported!");
  }
  remove(file: AbstractFile): void {
    console.log("Sorry, this method is not supported!");
  }
  getChild(i: number): null {
    console.log("Sorry, this method is not supported!");
    return null;
  }
  killVirus(): void {
    console.log(`Virus scan successful for image file: ${this.#name}`);
  }
}

2.2. Create a text file class, acting as a leaf component:

import { AbstractFile } from "./AbstractFile";

export class TextFile extends AbstractFile {
  #name: string;
  constructor(name: string) {
    super();
    this.#name = name;
  }
  add(file: AbstractFile): void {
    console.log("Sorry, this method is not supported!");
  }
  remove(file: AbstractFile): void {
    console.log("Sorry, this method is not supported!");
  }
  getChild(i: number): null {
    console.log("Sorry, this method is not supported!");
    return null;
  }
  killVirus(): void {
    console.log(`Virus scan successful for text file: ${this.#name}`);
  }
}

2.3. Create a video file class, acting as a leaf component:

import { AbstractFile } from "./AbstractFile";

export class VideoFile extends AbstractFile {
  #name: string;
  constructor(name: string) {
    super();
    this.#name = name;
  }
  add(file: AbstractFile): void {
    console.log("Sorry, this method is not supported!");
  }
  remove(file: AbstractFile): void {
    console.log("Sorry, this method is not supported!");
  }
  getChild(i: number): null {
    console.log("Sorry, this method is not supported!");
    return null;
  }
  killVirus(): void {
    console.log(`Virus scan successful for video file: ${this.#name}`);
  }
}

3. Create a folder class, acting as a composite component:

import { AbstractFile } from "./AbstractFile";

export class Folder extends AbstractFile {
  #name: string;
  #fileList: AbstractFile[] = [];
  constructor(name: string) {
    super();
    this.#name = name;
  }
  add(file: AbstractFile): void {
    this.#fileList.push(file);
  }
  remove(file: AbstractFile): void {
    const index = this.#fileList.indexOf(file);
    if (index > -1) {
      this.#fileList.splice(index, 1);
    }
  }
  getChild(i: number): AbstractFile {
    return this.#fileList[i];
  }
  killVirus(): void {
    console.log(`\nScanning folder ${this.#name} for viruses`);

    // Recursive call to the killVirus method of member components
    for (const file of this.#fileList) {
      file.killVirus();
    }
  }
}

4. Write a client test method:

import { Folder } from "./Folder";
import { ImageFile } from "./ImageFile";
import { TextFile } from "./TextFile";
import { VideoFile } from "./VideoFile";

export const CompositePatternClient = () => {
  const file1 = new ImageFile("DragonGirl.jpg"),
    file2 = new ImageFile("ZhangWuji.jpg"),
    file3 = new TextFile("NineYinManual.txt"),
    file4 = new TextFile("KuifuaTreasure.txt"),
    file5 = new VideoFile("SmilingProudly.rmvb");

  const folder1 = new Folder("Sunny'sFiles"),
    folder2 = new Folder("ImageFiles"),
    folder3 = new Folder("TextFiles"),
    folder4 = new Folder("VideoFiles");

  folder1.add(file1);
  folder2.add(file2);
  folder3.add(file3);
  folder3.add(file4);
  folder4.add(file5);
  folder1.add(folder2);
  folder1.add(folder3);
  folder1.add(folder4);

  // Start virus scan from the "Sunny'sFiles" node
  folder1.killVirus();

  // Start virus scan from the "VideoFiles" node
  folder4.killVirus();
};