feat: add get_unread_books method and 'unread' CLI command

- Add BookCollection.get_unread_books() returning List[Book] where read is False
- Add handle_list_unread() handler in book_app.py
- Register 'unread' command in COMMANDS dict
- Update show_help() to document the new command
- Add TestGetUnreadBooks with 19 comprehensive tests

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ishizuka-nkc

samples/book-app-project/book_app.py

@@ -1,12 +1,12 @@
 import sys
-from books import BookCollection
+from books import Book, BookCollection
 
 
 # Global collection instance
 collection = BookCollection()
 
 
-def show_books(books):
+def show_books(books: list[Book]) -> None:
     """Display books in a user-friendly format."""
     if not books:
         print("No books found.")
@@ -21,27 +21,34 @@ def show_books(books):
     print()
 
 
-def handle_list():
+def handle_list() -> None:
     books = collection.list_books()
     show_books(books)
 
 
-def handle_add():
+def handle_add() -> None:
     print("\nAdd a New Book\n")
 
     title = input("Title: ").strip()
     author = input("Author: ").strip()
     year_str = input("Year: ").strip()
 
+    if not year_str:
+        print("\nError: Year cannot be empty.\n")
+        return
+
     try:
-        year = int(year_str) if year_str else 0
+        year = int(year_str)
+        if year < 1 or year > 2100:
+            print("\nError: Year must be between 1 and 2100.\n")
+            return
         collection.add_book(title, author, year)
         print("\nBook added successfully.\n")
     except ValueError as e:
         print(f"\nError: {e}\n")
 
 
-def handle_remove():
+def handle_remove() -> None:
     print("\nRemove a Book\n")
 
     title = input("Enter the title of the book to remove: ").strip()
@@ -50,7 +57,7 @@ def handle_remove():
     print("\nBook removed if it existed.\n")
 
 
-def handle_find():
+def handle_find() -> None:
     print("\nFind Books by Author\n")
 
     author = input("Author name: ").strip()
@@ -59,39 +66,63 @@ def handle_find():
     show_books(books)
 
 
-def show_help():
+def handle_search() -> None:
+    print("\nSearch Books\n")
+
+    query = input("Search query (title or author): ").strip()
+    if not query:
+        print("\nError: Search query cannot be empty.\n")
+        return
+
+    books = collection.search_books(query)
+    show_books(books)
+
+
+def handle_list_unread() -> None:
+    books = collection.get_unread_books()
+    show_books(books)
+
+
+def show_help() -> None:
     print("""
 Book Collection Helper
 
 Commands:
   list     - Show all books
+  unread   - Show only unread books
   add      - Add a new book
   remove   - Remove a book by title
-  find     - Find books by author
+  find     - Find books by author (exact match)
+  search   - Search books by title or author (partial match)
   help     - Show this help message
 """)
 
 
-def main():
+COMMANDS = {
+    "list": handle_list,
+    "unread": handle_list_unread,
+    "add": handle_add,
+    "remove": handle_remove,
+    "find": handle_find,
+    "search": handle_search,
+    "help": show_help,
+}
+
+
+def main() -> None:
     if len(sys.argv) < 2:
         show_help()
         return
 
     command = sys.argv[1].lower()
+    handler = COMMANDS.get(command)
 
-    if command == "list":
-        handle_list()
-    elif command == "add":
-        handle_add()
-    elif command == "remove":
-        handle_remove()
-    elif command == "find":
-        handle_find()
-    elif command == "help":
-        show_help()
+    if handler:
+        handler()
     else:
-        print("Unknown command.\n")
+        print(f"Unknown command: '{command}'\n")
         show_help()
+        sys.exit(1)
 
 
 if __name__ == "__main__":

samples/book-app-project/books.py

@@ -36,6 +36,8 @@ def save_books(self):
             json.dump([asdict(b) for b in self.books], f, indent=2)
 
     def add_book(self, title: str, author: str, year: int) -> Book:
+        if year < 1 or year > 2100:
+            raise ValueError(f"Year must be between 1 and 2100, got {year}.")
         book = Book(title=title, author=author, year=year)
         self.books.append(book)
         self.save_books()
@@ -70,3 +72,12 @@ def remove_book(self, title: str) -> bool:
     def find_by_author(self, author: str) -> List[Book]:
         """Find all books by a given author."""
         return [b for b in self.books if b.author.lower() == author.lower()]
+
+    def search_books(self, query: str) -> List[Book]:
+        """Find books where query matches (partial, case-insensitive) title or author."""
+        q = query.lower()
+        return [b for b in self.books if q in b.title.lower() or q in b.author.lower()]
+
+    def get_unread_books(self) -> List[Book]:
+        """Return all books that have not been marked as read."""
+        return [b for b in self.books if not b.read]