package dev.banking.model;
import java.util.concurrent.locks.ReentrantLock;

public class BankAccount {

    private final int accountId;
    private long balance;

    /*
     * Students may introduce additional fields
     * such as:
     * - Lock / ReentrantLock
     * - ReadWriteLock
     * - Object monitor
     * - etc.
     */
    private final ReentrantLock lock = new ReentrantLock();

    public BankAccount(int accountId, long initialBalance) {
        this.accountId = accountId;
        this.balance = initialBalance;
    }

    public int getAccountId() {
        return accountId;
    }

    /*
     * TODO:
     * Return the current balance in a thread-safe way.
     *
     * Requirements:
     * - Must be safe under concurrent reads/writes
     * - Should not block unnecessarily if using read/write locks
     */
    public long getBalance() {
        lock.lock();
        try {
            return balance;
        } finally {
            lock.unlock();
        }
    }

    /*
     * TODO:
     * Increase balance atomically.
     *
     * Requirements:
     * - Must not lose updates under concurrency
     */
    public void deposit(long amount) {
        lock.lock();
        try {
            balance += amount;
        } finally {
            lock.unlock();
        }
    }

    /*
     * TODO:
     * Decrease balance atomically.
     *
     * Requirements:
     * - Must not cause race conditions
     * - Negative balance handling is NOT required unless you decide
     *   to extend the system (optional)
     */
    public void withdraw(long amount) {
        lock.lock();
        try {
            balance -= amount;
        } finally {
            lock.unlock();
        }
    }

    /*
     * TODO:
     * Transfer money between two accounts atomically.
     *
     * IMPORTANT REQUIREMENTS:
     * - Must be atomic (no partial transfer)
     * - Must be deadlock-free
     * - Must protect both source and target accounts
     *
     * HINT:
     * - Consider global lock ordering using accountId
     * - Or tryLock with retry strategy
     */
    public void transfer(BankAccount target, long amount) {

        BankAccount firstLock;
        BankAccount secondLock;

        if (this.accountId < target.accountId) {
            firstLock = this;
            secondLock = target;
        } else {
            firstLock = target;
            secondLock = this;
        }

        firstLock.lock.lock();
        secondLock.lock.lock();

        try {
            this.balance -= amount;
            target.balance += amount;
        } finally {
            secondLock.lock.unlock();
            firstLock.lock.unlock();
        }
    }
}