#include "ChatServer.h"

#include <QJsonObject>
#include <QJsonArray>
#include <QJsonDocument>
#include <QDateTime>
#include <QDebug>

// ─────────────────────────────────────────────────────────────────────────────
//  Constructor
// ─────────────────────────────────────────────────────────────────────────────
ChatServer::ChatServer(QObject *parent) : QTcpServer(parent)
{
}

// ─────────────────────────────────────────────────────────────────────────────
//  Qt calls this automatically when a new client connects
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::incomingConnection(qintptr socketDescriptor)
{
    auto *socket = new QTcpSocket(this);

    // Qt docs recommend checking setSocketDescriptor actually succeeded
    if (!socket->setSocketDescriptor(socketDescriptor)) {
        qWarning() << "[Server] Failed to set descriptor:" << socket->errorString();
        delete socket;
        return;
    }

    // wire up this socket's signals to our slots
    connect(socket, &QTcpSocket::readyRead,    this, &ChatServer::onReadyRead);
    connect(socket, &QTcpSocket::disconnected, this, &ChatServer::onDisconnected);

    m_clients[socket] = "";  // socket known, username not yet
    qInfo() << "[Server] New connection from" << socket->peerAddress().toString();

    sendSystemMessage(socket, QString("Connected to server. %1 user(s) online.")
                      .arg(m_clients.size()));
}

// ─────────────────────────────────────────────────────────────────────────────
//  Fires when data arrives from any client
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::onReadyRead()
{
    auto *socket = qobject_cast<QTcpSocket *>(sender());
    if (!socket) return;

    // append whatever arrived to this client's buffer
    m_buffers[socket] += socket->readAll();

    // guard against a client sending huge amounts of data with no newlines
    if (m_buffers[socket].size() > MAX_BUFFER_SIZE) {
        qWarning() << "[Server] Buffer overflow from"
                   << m_clients.value(socket, "unknown") << "— disconnecting.";
        socket->disconnectFromHost();
        return;
    }

    // extract and process complete messages (delimited by \n)
    while (m_buffers[socket].contains('\n')) {
        int idx         = m_buffers[socket].indexOf('\n');
        QByteArray line = m_buffers[socket].left(idx).trimmed();
        m_buffers[socket] = m_buffers[socket].mid(idx + 1);

        if (line.isEmpty()) continue;
        processFrame(socket, line);
    }
}

// ─────────────────────────────────────────────────────────────────────────────
//  Fires when a client disconnects
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::onDisconnected()
{
    // Qt docs: use deleteLater() when deleting sender() of disconnected signal
    auto *socket = qobject_cast<QTcpSocket *>(sender());
    if (!socket) return;

    QString username = m_clients.value(socket, "Unknown");
    m_clients.remove(socket);
    m_buffers.remove(socket);
    socket->deleteLater();

    qInfo() << "[Server]" << username << "disconnected.";
    broadcast(nullptr, buildFrame("system", "Server",
              username + " has left the chat.", ""));
    broadcastUserList();
}

// ─────────────────────────────────────────────────────────────────────────────
//  Handle one complete JSON message from a client
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::processFrame(QTcpSocket *socket, const QByteArray &data)
{
    // parse raw bytes into a JSON document
    QJsonParseError err;
    QJsonDocument doc = QJsonDocument::fromJson(data, &err);
    if (err.error != QJsonParseError::NoError || !doc.isObject()) {
        qWarning() << "[Server] Bad JSON from client:" << err.errorString();
        return;
    }

    QJsonObject obj  = doc.object();
    QString type     = obj["type"].toString();
    QString username = obj["username"].toString().trimmed();

    // ── JOIN ──────────────────────────────────────────────────────────────────
    if (type == "join") {
        if (username.isEmpty()) {
            sendSystemMessage(socket, "Username cannot be empty.");
            return;
        }

        // check for duplicate username (case insensitive)
        for (auto it = m_clients.begin(); it != m_clients.end(); ++it) {
            if (it.value().toLower() == username.toLower() && it.key() != socket) {
                sendSystemMessage(socket, "Username '" + username + "' is already taken.");
                return;
            }
        }

        m_clients[socket] = username;
        qInfo() << "[Server]" << username << "joined.";

        sendSystemMessage(socket, "Welcome, " + username + "!");
        broadcast(socket, buildFrame("system", "Server",
                  username + " joined the chat.", ""));
        broadcastUserList();
        return;
    }

    // ── GUARD: must have a username before doing anything else ────────────────
    if (m_clients.value(socket).isEmpty()) {
        sendSystemMessage(socket, "Please join with a username first.");
        return;
    }

    // ── MESSAGE ───────────────────────────────────────────────────────────────
    if (type == "message") {
        QString text = obj["text"].toString().trimmed();
        if (text.isEmpty()) return;

        QString ts = QDateTime::currentDateTime().toString("hh:mm");
        qInfo() << "[Server]" << username << ":" << text;
        broadcast(nullptr, buildFrame("message", username, text, ts));
    }
}

// ─────────────────────────────────────────────────────────────────────────────
//  Package data into a JSON frame ready to send
// ─────────────────────────────────────────────────────────────────────────────
QByteArray ChatServer::buildFrame(const QString &type, const QString &from,
                                   const QString &text, const QString &ts)
{
    QJsonObject obj;
    obj["type"] = type;
    obj["from"] = from;
    obj["text"] = text;
    obj["ts"]   = ts;
    // Compact = no spaces, everything on one line. \n is the message delimiter.
    return QJsonDocument(obj).toJson(QJsonDocument::Compact) + "\n";
}

// ─────────────────────────────────────────────────────────────────────────────
//  Send a frame to all clients, optionally excluding one
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::broadcast(QTcpSocket *exclude, const QByteArray &frame)
{
    for (auto *s : m_clients.keys()) {
        if (s != exclude && s->state() == QAbstractSocket::ConnectedState)
            s->write(frame);
    }
}

// ─────────────────────────────────────────────────────────────────────────────
//  Send a system notification to one specific client
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::sendSystemMessage(QTcpSocket *socket, const QString &text)
{
    socket->write(buildFrame("system", "Server", text, ""));
}

// ─────────────────────────────────────────────────────────────────────────────
//  Send the current online user list to all clients
// ─────────────────────────────────────────────────────────────────────────────
void ChatServer::broadcastUserList()
{
    // QJsonArray is explicitly included — don't rely on indirect includes
    QJsonArray names;
    for (const QString &name : m_clients.values())
        if (!name.isEmpty()) names.append(name);

    QJsonObject obj;
    obj["type"]  = "userlist";
    obj["users"] = names;

    QByteArray frame = QJsonDocument(obj).toJson(QJsonDocument::Compact) + "\n";
    for (auto *s : m_clients.keys())
        s->write(frame);
}