Sample USSD implementation for a friend

ussd.ts

type PageId = number;

type PageOption = {
  optionText: string;
  dialIndex: number;
  pageId: PageId;
};

class Page {
  id: PageId;
  title: string;
  pageOptions: PageOption[];

  constructor(title: string, options: PageOption[] = []) {
    this.pageOptions = options;
    this.id = Math.random();
    this.title = title;
  }

  addPageOption(option: PageOption) {
    this.pageOptions.push(option);
  }

  getPageOptionByDialindex(dialIndex: number): PageOption | undefined {
    return this.pageOptions.find(
      (pageOption) => pageOption.dialIndex === dialIndex
    );
  }

  print() {
    console.log(`
        ${this.pageOptions.reduce((finalString: string, option) => {
          finalString = finalString.concat(`

            ${option.dialIndex}. ${option.optionText}`);
          return finalString;
        }, `${this.title}`)}
    `);
  }
}

// Code is something like *555*
class UssdSystem {
  code: number;
  pages: Record<PageId, Page>;
  rootPageId: PageId;

  constructor(code: number, rootPage: Page) {
    this.pages = { ...this.pages, [rootPage.id]: rootPage };
    this.rootPageId = rootPage.id;
    this.code = code;
  }

  addPages(pages: Page[]): void {
    pages.forEach((page) => {
      this.pages = { ...this.pages, [page.id]: page };
    });
  }

  getPageById(id: PageId): Page {
    return this.pages[id];
  }

  // *number*number*number
  parsePathAndPrint(path: string) {
    const dialIndexPath = path.split("*").map((val) => Number(val));
    const rootPage = this.pages[this.rootPageId];
    let currentPageId: PageId = rootPage.id;

    for (let i = 0; i < dialIndexPath.length; i++) {
      const dialIndex = dialIndexPath[i];
      const pageOption =
        this.pages[currentPageId].getPageOptionByDialindex(dialIndex);
      if (pageOption) {
        currentPageId = pageOption.pageId;
      } else {
        // ERROR HANDLING
      }
    }
    this.pages[currentPageId].print();
  }
}

const createAirtimeBuyingUssd = (): UssdSystem => {
  const firstPage = new Page("Welcome To Our Service");
  const buyAirtimePage = new Page("Buy Airtime Here");
  const buyDataPage = new Page("Buy Data Here");
  const buyAirtimeFromBankPage = new Page("Buy From Your Bank Here");

  const rechargeCardSystem = new UssdSystem(555, firstPage);
  rechargeCardSystem.addPages([
    firstPage,
    buyAirtimePage,
    buyDataPage,
    buyAirtimeFromBankPage,
  ]);

  /// Start of populating the "first page"
  firstPage.addPageOption({
    dialIndex: 1,
    optionText: "Buy Airtime",
    pageId: buyAirtimePage.id,
  });
  firstPage.addPageOption({
    dialIndex: 2,
    optionText: "Buy Data",
    pageId: buyDataPage.id,
  });
  /// End of populating the first page

  /// Start of populating the "Buy Airtime page"
  buyAirtimePage.addPageOption({
    dialIndex: 99,
    optionText: "Go to first page",
    pageId: firstPage.id,
  });
  buyAirtimePage.addPageOption({
    dialIndex: 1,
    optionText: "Buy From Bank",
    pageId: buyAirtimeFromBankPage.id,
  });
  /// End of populating the "Buy Airtime page"

  /// Start of populating the "Buy Airtime page"
  buyDataPage.addPageOption({
    dialIndex: 99,
    optionText: "Go to first page",
    pageId: firstPage.id,
  });
  buyDataPage.addPageOption({
    dialIndex: 1,
    optionText: "Buy From Bank",
    pageId: buyAirtimeFromBankPage.id,
  });
  /// End of populating the "Buy Airtime page"

  /// Start of populating the "Buy From Your Bank"
  buyAirtimeFromBankPage.addPageOption({
    dialIndex: 99,
    optionText: "Go to first page",
    pageId: firstPage.id,
  });
  /// End of populating the "Buy From Your Bank"

  return rechargeCardSystem;
};

const rechargeCardSystem = createAirtimeBuyingUssd();

rechargeCardSystem.parsePathAndPrint("1*1");