package dev.banking.model;

import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class BankAccount {

    private final int accountId;
    private long balance;

    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final ReentrantLock transferLock = new ReentrantLock();

    /*
     * Students may introduce additional fields
     * such as:
     * - Lock / ReentrantLock
     * - ReadWriteLock
     * - Object monitor
     * - etc.
     */

    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() {
       rwLock.readLock().lock();
       try {
           return balance;
       } finally {
           rwLock.readLock().unlock();
       }
    }

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

        if (this.getAccountId() < target.getAccountId()) {
            first = this;
            second = target;
        } else {
            first = target;
            second = this;
        }

        first.transferLock.lock();

        try {
            second.transferLock.lock();
            try {
                first.balance -= amount;
                target.balance += amount;
            } finally {
                second.transferLock.unlock();
            }
        } finally {
            first.transferLock.unlock();
        }
    }
}