import re
import datetime
import json


available_books = []
borrowed_books = {}

def load_data():
    global available_books, borrowed_books

    # Load available books
    try:
        with open("books.txt", "r", encoding="utf-8") as f:
            available_books = [line.strip() for line in f if line.strip()]
    except FileNotFoundError:
        pass

    # Load borrowed books
    borrowed_books = {}
    try:
        with open("borrowed_books.txt", "r", encoding="utf-8") as f:
            for line in f:
                parts = line.strip().split("|")
                if len(parts) < 2:
                    continue
                title = parts[0]
                borrowed_books[title] = {
                    "name": parts[1],
                    "first_name": parts[2] if len(parts) > 2 else "",
                    "last_name": parts[3] if len(parts) > 3 else "",
                    "email": parts[4] if len(parts) > 4 else "",
                    "due": parts[5] if len(parts) > 5 else "",
                    "emailed": parts[6].lower() == "true" if len(parts) > 6 else False,
                }
    except FileNotFoundError:
        pass


def save_data():
    with open("books.txt", "w", encoding="utf-8") as f:
        for book in available_books:
            f.write(book + "\n")

    with open("borrowed_books.txt", "w", encoding="utf-8") as f:
        for title, data in borrowed_books.items():
            f.write(
                "|".join([
                    title,
                    data.get("name", ""),
                    data.get("first_name", ""),
                    data.get("last_name", ""),
                    data.get("email", ""),
                    data.get("due", ""),
                    str(data.get("emailed", False))
                ]) + "\n"
            )


def generate_email(first, last):
    first = re.sub(r"[^a-zA-Z]", "", first).lower()
    last = re.sub(r"[^a-zA-Z]", "", last).lower()
    if not first and not last:
        return ""
    return f"{first}.{last}@bourne-grammar.lincs.sch.uk"


def display_menu():
    print("\nLibrary Menu")
    print("1. View books")
    print("2. Borrow a book")
    print("3. Return a book")
    print("4. Exit")

def view_books():
    print("\nAvailable books:")
    if available_books:
        for i, book in enumerate(available_books, 1):
            print(f" {i}. {book}")
    else:
        print(" None")

    print("\nBorrowed books:")
    if borrowed_books:
        for i, (title, info) in enumerate(borrowed_books.items(), 1):
            print(f" {i}. {title} (borrowed by {info['name']}, due {info['due']})")
    else:
        print(" None")

def borrow_book():
    if not available_books:
        print("No books available.")
        return

    view_books()
    choice = input("Select book number: ")
    if not choice.isdigit():
        return

    idx = int(choice) - 1
    if idx < 0 or idx >= len(available_books):
        return

    first = input("First name: ")
    last = input("Last name: ")
    if not first and not last:
        print("Name required.")
        return

    title = available_books.pop(idx)
    due = (datetime.date.today() + datetime.timedelta(days=14)).isoformat()

    borrowed_books[title] = {
        "name": f"{first} {last}".strip(),
        "first_name": first,
        "last_name": last,
        "email": generate_email(first, last),
        "due": due,
        "emailed": False
    }

    save_data()
    print(f"Borrowed '{title}'")

def return_book():
    if not borrowed_books:
        print("No borrowed books.")
        return

    titles = list(borrowed_books.keys())
    for i, title in enumerate(titles, 1):
        print(f" {i}. {title}")

    choice = input("Select book number: ")
    if not choice.isdigit():
        return

    idx = int(choice) - 1
    if idx < 0 or idx >= len(titles):
        return

    title = titles[idx]
    del borrowed_books[title]
    available_books.append(title)

    save_data()
    print(f"Returned '{title}'")


load_data()

while True:
    display_menu()
    choice = input("Choose (1-4): ")

    if choice == "1":
        view_books()
    elif choice == "2":
        borrow_book()
    elif choice == "3":
        return_book()
    elif choice == "4":
        save_data()
        print("Goodbye.")
        break