Project 7 — The Library Management System

// library.cpp — Programming Fundamentals Using C++
// Project 7 · The Library Management System
// Build: g++ -std=c++17 -Wall -Wextra library.cpp -o library

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <stdexcept>
using namespace std;

// Format contract — books.csv, one record per line:
//   title,author,copies,initial
//   (no commas inside title/author; 1 <= initial <= 99; 0 <= copies <= initial)
// This comment governs BOTH loadBooks and saveBooks; change them together.

struct Book {
    string title, author;
    int copies, initial;
};

void seedIfMissing(const string& path) {
    ifstream probe(path);
    if (probe) return;                       // file exists: nothing to seed
    ofstream out(path);
    out << "Clean Code,Martin,2,2\n";
    out << "Algorithms,Cormen,1,3\n";
    out << "C++ Primer,Lippman,3,3\n";
}

int loadBooks(const string& path, vector<Book>& out) {
    ifstream in(path);
    if (!in) return 0;
    string line;
    int skipped = 0;
    while (getline(in, line)) {              // read the line, then the line's end
        if (line.empty()) continue;
        size_t c1 = line.find(',');
        size_t c2 = (c1 == string::npos) ? string::npos : line.find(',', c1 + 1);
        size_t c3 = (c2 == string::npos) ? string::npos : line.find(',', c2 + 1);
        if (c3 == string::npos) { ++skipped; continue; }
        try {
            Book b;
            b.title   = line.substr(0, c1);
            b.author  = line.substr(c1 + 1, c2 - c1 - 1);
            b.copies  = stoi(line.substr(c2 + 1, c3 - c2 - 1));
            b.initial = stoi(line.substr(c3 + 1));
            bool valid = !b.title.empty() && !b.author.empty()
                         && b.initial >= 1 && b.initial <= 99
                         && b.copies >= 0 && b.copies <= b.initial;
            if (!valid) { ++skipped; continue; }
            out.push_back(b);
        } catch (const exception&) {          // stoi refused: malformed line
            ++skipped;
        }
    }
    return skipped;
}

void saveBooks(const string& path, const vector<Book>& books) {
    ofstream out(path);                       // truncating: the whole library is rewritten
    for (const Book& b : books)
        out << b.title << "," << b.author << "," << b.copies << "," << b.initial << "\n";
}

Book* findBook(vector<Book>& books, const string& title) {
    for (Book& b : books)
        if (b.title == title) return &b;
    return nullptr;
}

void listAll(const vector<Book>& books) {
    if (books.empty()) { cout << "Library empty\n"; return; }
    for (const Book& b : books)
        cout << "  " << b.title << " by " << b.author
             << " (" << b.copies << "/" << b.initial << " available)\n";
}

void searchByPrefix(const vector<Book>& books, const string& prefix) {
    bool any = false;
    for (const Book& b : books)
        if (b.title.find(prefix) == 0) {      // prefix = find at position 0
            cout << "  " << b.title << " by " << b.author << "\n";
            any = true;
        }
    if (!any) cout << "  no matches\n";
}

bool borrowBook(Book& b) {                    // the state transition, bounded
    if (b.copies <= 0) return false;
    --b.copies;
    return true;
}

bool returnBook(Book& b) {
    if (b.copies >= b.initial) return false;
    ++b.copies;
    return true;
}

bool addBook(vector<Book>& books, const Book& candidate) {
    if (findBook(books, candidate.title) != nullptr) return false;   // duplicate title
    if (candidate.initial < 1 || candidate.initial > 99) return false;
    if (candidate.copies < 0 || candidate.copies > candidate.initial) return false;
    books.push_back(candidate);
    return true;
}

int main() {
    const string PATH = "books.csv";
    seedIfMissing(PATH);

    vector<Book> books;
    int skipped = loadBooks(PATH, books);
    if (skipped) cout << "Skipped " << skipped << " malformed line(s)\n";
    cout << "Loaded " << books.size() << " books\n";

    int choice;
    do {
        cout << "\n1 List · 2 Search · 3 Borrow · 4 Return · 5 Add · 6 Save · 0 Save & quit: ";
        cin >> choice;
        cin.ignore(1000, '\n');

        if (choice == 1) {
            listAll(books);
        } else if (choice == 2) {
            cout << "Title (or prefix): ";
            string prefix; getline(cin, prefix);
            searchByPrefix(books, prefix);
        } else if (choice == 3 || choice == 4) {
            cout << "Title: ";
            string title; getline(cin, title);
            Book* b = findBook(books, title);
            if (!b) { cout << "No such book\n"; continue; }
            bool ok = (choice == 3) ? borrowBook(*b) : returnBook(*b);
            if (ok) cout << (choice == 3 ? "Borrowed — " : "Returned — ")
                         << b->copies << " of " << b->initial << " available\n";
            else    cout << "Refused: "
                         << (choice == 3 ? "no copies left" : "already at initial count")
                         << "\n";
        } else if (choice == 5) {
            Book candidate;
            cout << "Title: ";  getline(cin, candidate.title);
            cout << "Author: "; getline(cin, candidate.author);
            cout << "Initial copies (1-99): ";
            cin >> candidate.initial;
            candidate.copies = candidate.initial;
            if (addBook(books, candidate)) cout << "Added\n";
            else cout << "Refused: duplicate title or invalid counts\n";
            cin.ignore(1000, '\n');
        } else if (choice == 6) {
            saveBooks(PATH, books);
            cout << "Saved " << books.size() << " books\n";
        } else if (choice != 0) {
            cout << "Invalid choice\n";
        }
    } while (choice != 0);

    saveBooks(PATH, books);
    cout << "Saved " << books.size() << " books — goodbye\n";
    return 0;
}