library.cpp

#include <iostream>
#include <string>
#include <vector>
#include <limits>       // For numeric_limits
#include <algorithm>    // For std::transform, std::remove, std::remove_if
#include <fstream>      // For file handling (CSV)
#include <sstream>      // For string stream parsing (CSV)
#include <cctype>       // For ::tolower

using namespace std;

// --- Utility Functions ---

// Utility function to handle the input stream state after using cin >> int
void clearInputBuffer() {
    // Uses numeric_limits to ignore the maximum possible number of characters up to the newline
    if (cin.fail()) {
        cin.clear();
    }
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

// Utility function to convert a string to lowercase
string toLower(const string& str) {
    string data = str;
    // Use std::tolower from <cctype>
    transform(data.begin(), data.end(), data.begin(),
        [](unsigned char c){ return std::tolower(c); });
    return data;
}

// --- Book Class Definition ---
class Book {
private:
    string bookID;
    string title;
    string author;
    bool isIssued;

public:
    // Constructor
    Book(string id, string t, string a)
        : bookID(id), title(t), author(a), isIssued(false) {}

    // Getters
    string getBookID() const { return bookID; }
    string getTitle() const { return title; }
    string getAuthor() const { return author; }
    bool getIsIssued() const { return isIssued; }

    // Mutator methods for status
    bool issueBook() {
        if (isIssued) {
            return false;
        }
        isIssued = true;
        return true;
    }

    void returnBook() {
        isIssued = false;
    }
    
    // Setter for loading data from file
    void setIsIssued(bool issued) {
        isIssued = issued;
    }

    void display() const {
        cout << " --- Book Details ---\n";
        cout << " ID: " << bookID << "\n";
        cout << " Title: " << title << "\n";
        cout << " Author: " << author << "\n";
        cout << " Status: " << (isIssued ? "Issued" : "Available") << "\n";
    }
};

// --- Member Class Definition ---
class Member {
private:
    string memberID;
    string name;
    vector<string> issuedBookIDs;

public:
    // Constructor
    Member(string id, string n) : memberID(id), name(n) {}
    
    // Overload for loading from CSV with issued books
    Member(string id, string n, const vector<string>& issuedIDs) 
        : memberID(id), name(n), issuedBookIDs(issuedIDs) {}

    // Getters
    string getMemberID() const { return memberID; }
    string getName() const { return name; }
    const vector<string>& getIssuedBookIDs() const { return issuedBookIDs; } 

    void issueBook(string bookID) {
        issuedBookIDs.push_back(bookID);
    }

    void returnBook(const string& bookID) {
        // Use erase-remove idiom for efficient and correct vector removal
        auto it = std::remove(issuedBookIDs.begin(), issuedBookIDs.end(), bookID);
        issuedBookIDs.erase(it, issuedBookIDs.end());
    }

    void display() const {
        cout << " --- Member Details ---\n";
        cout << " Member ID: " << memberID << "\n";
        cout << " Name: " << name << "\n";
        cout << " Books Issued: " << issuedBookIDs.size() << "\n";
        if (!issuedBookIDs.empty()) {
            cout << " Issued Book IDs: ";
            for (const string& id : issuedBookIDs) {
                cout << id << " ";
            }
            cout << "\n";
        }
    }
};

// --- Library Class Definition ---
class Library {
private:
    vector<Book> books;
    vector<Member> members;

    // Helper functions (const and non-const versions)
    Book* findBookByID(const string& bookID) {
        for (Book& b : books) {
            if (b.getBookID() == bookID) {
                return &b;
            }
        }
        return nullptr;
    }

    Member* findMemberByID(const string& memberID) {
        for (Member& m : members) {
            if (m.getMemberID() == memberID) {
                return &m;
            }
        }
        return nullptr;
    }
    
    const Member* findMemberByIDConst(const string& memberID) const {
        for (const Member& m : members) {
            if (m.getMemberID() == memberID) {
                return &m;
            }
        }
        return nullptr;
    }
    
    bool memberHasBook(const Member* member, const string& bookID) const {
        for (const string& id : member->getIssuedBookIDs()) {
            if (id == bookID) {
                return true;
            }
        }
        return false;
    }

public:
    // --- Core Management Functions ---

    void addBook() {
        string id, title, author;
        
        cout << "Enter Book ID: ";
        getline(cin, id);

        if (findBookByID(id) != nullptr) {
            cout << "\nError: A Book with ID '" << id << "' already exists. Addition failed.\n";
            return;
        }

        cout << "Enter Title: ";
        getline(cin, title);
        cout << "Enter Author: ";
        getline(cin, author);

        books.emplace_back(id, title, author);
        cout << "\nSuccess: Book '" << title << "' added.\n";
    }
    
    void removeBook() {
        string id;
        cout << "Enter Book ID to remove: ";
        getline(cin, id);

        // Find and erase the book using erase-remove idiom with a lambda
        auto it = std::remove_if(books.begin(), books.end(), 
            [&](const Book& b) { 
                return b.getBookID() == id; 
            });

        if (it != books.end()) {
            string title = it->getTitle();
            books.erase(it, books.end());
            
            // Remove book ID from all members' issued lists to maintain consistency
            for (Member& m : members) {
                m.returnBook(id); 
            }
            cout << "\nSuccess: Book '" << title << "' (ID: " << id << ") removed.\n";
        } else {
            cout << "\nError: Book with ID '" << id << "' not found.\n";
        }
    }

    void addMember() {
        string id, name;
        cout << "Enter Member ID: ";
        getline(cin, id);

        if (findMemberByID(id) != nullptr) {
            cout << "\nError: A Member with ID '" << id << "' already exists. Registration failed.\n";
            return;
        }

        cout << "Enter Member Name: ";
        getline(cin, name);

        members.emplace_back(id, name);
        cout << "\nSuccess: Member '" << name << "' added.\n";
    }

    void removeMember() {
        string id;
        cout << "Enter Member ID to remove: ";
        getline(cin, id);

        // Find the member iterator before removal
        auto member_it = std::find_if(members.begin(), members.end(), 
            [&](const Member& m) { return m.getMemberID() == id; });

        if (member_it != members.end()) {
            string name = member_it->getName();
            const vector<string>& issuedIDs = member_it->getIssuedBookIDs();
            
            if (!issuedIDs.empty()) {
                cout << "\nError: Member '" << name << "' still has " << issuedIDs.size() << " book(s) issued. Please return them first.\n";
                return;
            }

            members.erase(member_it);
            cout << "\nSuccess: Member '" << name << "' (ID: " << id << ") removed.\n";
        } else {
            cout << "\nError: Member with ID '" << id << "' not found.\n";
        }
    }

    void issueBook() {
        string memberID, bookID;
        cout << "Enter Member ID: ";
        getline(cin, memberID);
        cout << "Enter Book ID: ";
        getline(cin, bookID);

        Member* member = findMemberByID(memberID);
        if (member == nullptr) {
            cout << "\nError: Member not found with ID " << memberID << ".\n";
            return;
        }

        Book* book = findBookByID(bookID);
        if (book == nullptr) {
            cout << "\nError: Book not found with ID " << bookID << ".\n";
            return;
        }

        if (book->issueBook()) {
            member->issueBook(bookID);
            cout << "\nSuccess: Book '" << book->getTitle() << "' issued to " << member->getName() << ".\n";
        } else {
            cout << "\nError: Book '" << book->getTitle() << "' is already issued.\n";
        }
    }

    void returnBook() {
        string memberID, bookID;
        cout << "Enter Member ID: ";
        getline(cin, memberID);
        cout << "Enter Book ID: ";
        getline(cin, bookID);

        Member* member = findMemberByID(memberID);
        if (member == nullptr) {
            cout << "\nError: Member not found with ID " << memberID << ".\n";
            return;
        }

        Book* book = findBookByID(bookID);
        if (book == nullptr) {
            cout << "\nError: Book not found with ID " << bookID << ".\n";
            return;
        }

        if (!book->getIsIssued()) {
             cout << "\nError: Book '" << book->getTitle() << "' is not currently marked as issued.\n";
             return;
        }
        
        // Note: Even if the member doesn't explicitly list the book, we perform the return 
        // to correct the book's status and clean the member's list if possible.
        
        book->returnBook();
        member->returnBook(bookID); 
        
        cout << "\nSuccess: Book '" << book->getTitle() << "' returned by " << member->getName() << ".\n";
    }

    // --- Display and Search Functions ---

    void searchBooks() const {
        string query;
        cout << "Enter title or author search query: ";
        getline(cin, query);

        string lowerQuery = toLower(query);
        vector<const Book*> results;

        for (const Book& b : books) {
            string lowerTitle = toLower(b.getTitle());
            string lowerAuthor = toLower(b.getAuthor());

            if (lowerTitle.find(lowerQuery) != string::npos || 
                lowerAuthor.find(lowerQuery) != string::npos) {
                results.push_back(&b);
            }
        }

        cout << "\n--- Search Results (" << results.size() << " found) ---\n";
        if (results.empty()) {
            cout << "No books matched your query: '" << query << "'.\n";
        } else {
            for (const Book* b : results) {
                b->display();
                cout << "----------------------------\n";
            }
        }
    }

    void showAllBooks() const {
        if (books.empty()) {
            cout << "\n--- Library Book Catalog ---\n";
            cout << "No books in the library.\n";
            return;
        }
        cout << "\n--- Library Book Catalog (" << books.size() << " total) ---\n";
        for (const Book& b : books) {
            b.display();
            cout << "----------------------------\n";
        }
    }

    void showAllMembers() const {
        if (members.empty()) {
            cout << "\n--- Library Member List ---\n";
            cout << "No members registered in the library.\n";
            return;
        }
        cout << "\n--- Library Member List (" << members.size() << " total) ---\n";
        for (const Member& m : members) {
            m.display();
            cout << "----------------------------\n";
        }
    }

    // --- CSV Save/Load Functionality ---

    void saveBooksToCSV() const {
        ofstream outFile("books.csv");
        if (!outFile.is_open()) {
            cout << "\nError: Could not open 'books.csv' for saving.\n";
            return;
        }

        // Header
        outFile << "BookID,Title,Author,IsIssued\n";

        for (const Book& b : books) {
            outFile << b.getBookID() << ","
                    << b.getTitle() << ","
                    << b.getAuthor() << ","
                    << (b.getIsIssued() ? 1 : 0) << "\n";
        }

        outFile.close();
        cout << "\nSuccess: " << books.size() << " books saved to 'books.csv'.\n";
    }

    void loadBooksFromCSV() {
        ifstream inFile("books.csv");
        if (!inFile.is_open()) {
            cout << "\nWarning: 'books.csv' not found or could not be opened. No book data loaded.\n";
            return;
        }

        string line;
        // Skip header line
        getline(inFile, line); 

        int loadedCount = 0;
        int duplicateCount = 0;
        
        while (getline(inFile, line)) {
            stringstream ss(line);
            string id, title, author, issuedStatusStr;
            int issuedInt;

            if (getline(ss, id, ',') &&
                getline(ss, title, ',') &&
                getline(ss, author, ',') &&
                (ss >> issuedInt)) { 

                if (findBookByID(id) == nullptr) {
                    Book newBook(id, title, author);
                    if (issuedInt == 1) {
                        newBook.setIsIssued(true);
                    }
                    books.push_back(newBook);
                    loadedCount++;
                } else {
                    duplicateCount++;
                }
            }
        }

        inFile.close();
        cout << "\nSuccess: Loaded " << loadedCount << " new books from 'books.csv'. "
             << (duplicateCount > 0 ? to_string(duplicateCount) + " duplicates skipped." : "") << "\n";
    }
    
    void saveMembersToCSV() const {
        ofstream outFile("members.csv");
        if (!outFile.is_open()) {
            cout << "\nError: Could not open 'members.csv' for saving.\n";
            return;
        }

        // Header
        outFile << "MemberID,Name,IssuedBookIDs\n";

        for (const Member& m : members) {
            outFile << m.getMemberID() << ","
                    << m.getName() << ",";
                    
            // Join all issued book IDs with a semicolon (;)
            const vector<string>& issuedIDs = m.getIssuedBookIDs();
            for (size_t i = 0; i < issuedIDs.size(); ++i) {
                outFile << issuedIDs[i];
                if (i < issuedIDs.size() - 1) {
                    outFile << ";"; 
                }
            }
            outFile << "\n";
        }

        outFile.close();
        cout << "\nSuccess: " << members.size() << " members saved to 'members.csv'.\n";
    }

    void loadMembersFromCSV() {
        ifstream inFile("members.csv");
        if (!inFile.is_open()) {
            cout << "\nWarning: 'members.csv' not found or could not be opened. No member data loaded.\n";
            return;
        }

        string line;
        // Skip header line
        getline(inFile, line); 

        int loadedCount = 0;
        int duplicateCount = 0;
        
        while (getline(inFile, line)) {
            stringstream ss(line);
            string id, name, issuedIDsStr;

            if (getline(ss, id, ',') &&
                getline(ss, name, ',') &&
                getline(ss, issuedIDsStr)) { 

                // 1. Parse Issued Book IDs by splitting the string stream by ';'
                vector<string> issuedIDs;
                stringstream issuedSS(issuedIDsStr);
                string bookID;
                
                while (getline(issuedSS, bookID, ';')) {
                    if (!bookID.empty()) {
                        issuedIDs.push_back(bookID);
                    }
                }
                
                // 2. Add Member (check for duplicates)
                if (findMemberByID(id) == nullptr) {
                    members.emplace_back(id, name, issuedIDs);
                    loadedCount++;
                } else {
                    duplicateCount++;
                }
            }
        }

        inFile.close();
        cout << "\nSuccess: Loaded " << loadedCount << " new members from 'members.csv'. "
             << (duplicateCount > 0 ? to_string(duplicateCount) + " duplicates skipped." : "") << "\n";
    }
};

// Displays the main menu options
void showMenu() {
    cout << "\n===== Library Management System =====\n";
    cout << "1. Add New Book\n";
    cout << "2. Register New Member\n";
    cout << "3. Issue a Book\n";
    cout << "4. Return a Book\n";
    cout << "5. Show All Books\n";
    cout << "6. Show All Members\n";
    cout << "7. Search Books (Title/Author)\n";
    cout << "8. Remove Book\n";
    cout << "9. Remove Member\n";
    cout << "10. Save Books to CSV\n";
    cout << "11. Load Books from CSV\n";
    cout << "12. Save Members to CSV\n";
    cout << "13. Load Members from CSV\n";
    cout << "14. Exit\n";
    cout << "=====================================\n";
    cout << "Enter your choice (1-14): ";
}

// --- Main Program Loop ---
int main() {
    // Ensure the console starts clean
    cout << "Welcome! Library Management System is ready.\n";
    
    // Create the library object
    Library myLibrary;
    int choice;

    cout << "\nAttempting to load persistent data...\n";
    myLibrary.loadBooksFromCSV();
    myLibrary.loadMembersFromCSV();
    cout << "Data loading complete.\n";
    
    while (true) {
        showMenu();
        
        // Use temporary stream variable to handle potential bad input before cin >> choice
        if (!(cin >> choice)) {
            clearInputBuffer(); // Clear the bad input
            cout << "\nError: Invalid input. Please enter a number (1-14).\n";
            continue;
        }

        // Clear the buffer after successful int read to prepare for subsequent getline() calls
        clearInputBuffer(); 

        switch (choice) {
            case 1:
                cout << "\n--- Add New Book ---\n";
                myLibrary.addBook();
                break;
            case 2:
                cout << "\n--- Register New Member ---\n";
                myLibrary.addMember();
                break;
            case 3:
                cout << "\n--- Issue a Book ---\n";
                myLibrary.issueBook();
                break;
            case 4:
                cout << "\n--- Return a Book ---\n";
                myLibrary.returnBook();
                break;
            case 5:
                myLibrary.showAllBooks();
                break;
            case 6:
                myLibrary.showAllMembers();
                break;
            case 7:
                cout << "\n--- Search Library ---\n";
                myLibrary.searchBooks();
                break;
            case 8:
                cout << "\n--- Remove Book ---\n";
                myLibrary.removeBook();
                break;
            case 9:
                cout << "\n--- Remove Member ---\n";
                myLibrary.removeMember();
                break;
            case 10:
                cout << "\n--- Saving Book Data ---\n";
                myLibrary.saveBooksToCSV();
                break;
            case 11:
                cout << "\n--- Loading Book Data ---\n";
                myLibrary.loadBooksFromCSV();
                break;
            case 12:
                cout << "\n--- Saving Member Data ---\n";
                myLibrary.saveMembersToCSV();
                break;
            case 13:
                cout << "\n--- Loading Member Data ---\n";
                myLibrary.loadMembersFromCSV();
                break;
            case 14:
                cout << "\nSaving all data before exit...\n";
                myLibrary.saveBooksToCSV();
                myLibrary.saveMembersToCSV();
                cout << "Thank you for using the Library Management System. Goodbye!\n";
                return 0;
            default:
                cout << "\nError: Invalid choice. Please select from 1-14.\n";
                break;
        }
    }

    return 0;
}