Project 4 — Design Library Management System

classDiagram
    class Library {
        -catalog: BookCatalog
        -members: Member[]
        +searchBook(query: string): Book[]
        +borrowBook(member: Member, book: Book): Borrowing
        +returnBook(borrowing: Borrowing): double
        +registerMember(name: string): Member
    }
    class BookCatalog {
        -books: Book[]
        +addBook(book: Book): void
        +search(query: string): Book[]
        +findByIsbn(isbn: string): Book
    }
    class Book {
        +isbn: string
        +title: string
        +author: string
        +genre: string
        +totalCopies: int
        -availableCopies: int
        +isAvailable(): boolean
        +borrow(): boolean
        +return(): void
    }
    class Member {
        +id: string
        +name: string
        -borrowedBooks: Borrowing[]
        +canBorrow(): boolean
        +getOutstandingFine(): double
    }
    class Borrowing {
        +id: string
        +book: Book
        +member: Member
        +borrowDate: Date
        +dueDate: Date
        +returnDate: Date
        +calculateFine(): double
    }

    Library --> BookCatalog
    Library *-- Member
    Member *-- Borrowing
    Borrowing --> Book

class Book {
  constructor(
    public isbn: string,
    public title: string,
    public author: string,
    public genre: string,
    public totalCopies: number,
    private availableCopies: number = totalCopies
  ) {}

  isAvailable(): boolean { return this.availableCopies > 0; }

  borrow(): boolean {
    if (!this.isAvailable()) return false;
    this.availableCopies--;
    return true;
  }

  returnBook(): void { this.availableCopies++; }
}

class Member {
  public borrowedBooks: Borrowing[] = [];

  constructor(public id: string, public name: string) {}

  canBorrow(): boolean {
    const active = this.borrowedBooks.filter(b => !b.returnDate).length;
    return active < 5;
  }

  getOutstandingFine(): number {
    return this.borrowedBooks
      .filter(b => !b.returnDate)
      .reduce((sum, b) => sum + b.calculateFine(), 0);
  }
}

class Borrowing {
  public borrowDate: Date = new Date();
  public dueDate: Date = new Date(Date.now() + 14 * 24 * 60 * 60 * 1000);
  public returnDate?: Date;

  constructor(public book: Book, public member: Member) {}

  calculateFine(): number {
    if (!this.returnDate) {
      const now = new Date();
      if (now <= this.dueDate) return 0;
      const daysOverdue = Math.ceil((now.getTime() - this.dueDate.getTime()) / (1000 * 60 * 60 * 24));
      return daysOverdue * 0.5; // $0.50/day
    }
    return 0;
  }
}