#include "rpc/RpcConnection.hpp"

#include <QJsonArray>
#include <QJsonDocument>
#include <QLocalSocket>
#include <QTimer>

#include "rpc/Protocol.hpp"
#include "velox_proto.hpp"

namespace velox::gui::rpc {
namespace {

constexpr int kStateDisconnected = int(ConnectionState::Disconnected);
constexpr int kStateConnecting = int(ConnectionState::Connecting);
constexpr int kStateHandshaking = int(ConnectionState::Handshaking);
constexpr int kStateConnected = int(ConnectionState::Connected);
constexpr int kStateReconnecting = int(ConnectionState::Reconnecting);

QJsonObject makeErrorEnvelope(int code, const QString &message) {
    QJsonObject err{{"code", code}, {"message", message}};
    return QJsonObject{{"jsonrpc", "2.0"}, {"error", err}};
}

QString contractProtocolVersion() {
    const auto v = velox::proto::kProtocolVersion;
    return QString::fromUtf8(v.data(), static_cast<qsizetype>(v.size()));
}

}  // namespace

RpcConnection::RpcConnection(QString socketPath, QObject *parent)
    : QObject(parent), socketPath_(std::move(socketPath)) {
    socket_ = new QLocalSocket(this);
    connect(socket_, &QLocalSocket::connected, this, &RpcConnection::onConnected);
    connect(socket_, &QLocalSocket::disconnected, this, &RpcConnection::onDisconnected);
    connect(socket_, &QLocalSocket::errorOccurred, this, &RpcConnection::onErrorOccurred);
    connect(socket_, &QLocalSocket::readyRead, this, &RpcConnection::onReadyRead);

    reconnectTimer_ = new QTimer(this);
    reconnectTimer_->setSingleShot(true);
    connect(reconnectTimer_, &QTimer::timeout, this, &RpcConnection::attemptReconnect);
}

RpcConnection::~RpcConnection() = default;

void RpcConnection::start() {
    if (wantConnected_) {
        return;
    }
    wantConnected_ = true;
    backoffMs_ = kMinBackoffMs;
    setState(kStateConnecting);
    socket_->connectToServer(socketPath_);
}

void RpcConnection::stop() {
    wantConnected_ = false;
    reconnectTimer_->stop();
    socket_->abort();
    rxBuffer_.clear();
    // Fail any in-flight callbacks so RpcClient does not leak them.
    const auto tags = pendingTags_.values();
    pendingTags_.clear();
    for (const quint64 tag : tags) {
        emit callCompleted(tag, makeErrorEnvelope(-1, QStringLiteral("connection stopped")));
    }
    setState(kStateDisconnected);
}

void RpcConnection::sendCall(quint64 tag, const QString &methodName, const QJsonObject &params) {
    if (state_ != kStateConnected) {
        emit callCompleted(tag, makeErrorEnvelope(-1, QStringLiteral("not connected")));
        return;
    }
    const qint64 id = nextRpcId_++;
    pendingTags_.insert(id, tag);
    sendRaw(id, methodName, params);
}

void RpcConnection::onConnected() {
    rxBuffer_.clear();
    beginHandshake();
}

void RpcConnection::beginHandshake() {
    setState(kStateHandshaking);
    sendRaw(kHelloId, QString::fromLatin1(method::kSessionHello),
            QJsonObject{{"clientType", "gui"},
                        {"clientName", QStringLiteral("velox-gui 0.1.0")},
                        {"protocolVersion", contractProtocolVersion()}});
}

// A dropped connection surfaces as disconnected(); a *failed* connect attempt surfaces as
// errorOccurred() with no disconnected() to follow. Both funnel here, and the isActive()
// guard means the two firing together for one failure only arms one timer.
void RpcConnection::scheduleReconnect() {
    if (!wantConnected_) {
        setState(kStateDisconnected);
        return;
    }
    if (reconnectTimer_->isActive()) {
        return;
    }
    setState(kStateReconnecting);
    reconnectTimer_->start(backoffMs_);
    backoffMs_ = qMin(backoffMs_ * 2, kMaxBackoffMs);
}

void RpcConnection::onDisconnected() {
    scheduleReconnect();
}

void RpcConnection::onErrorOccurred() {
    scheduleReconnect();
}

void RpcConnection::attemptReconnect() {
    if (!wantConnected_) {
        return;
    }
    setState(kStateConnecting);
    socket_->abort();
    socket_->connectToServer(socketPath_);
}

void RpcConnection::onReadyRead() {
    rxBuffer_ += socket_->readAll();
    int nl = rxBuffer_.indexOf('\n');
    while (nl != -1) {
        const QByteArray line = rxBuffer_.left(nl).trimmed();
        rxBuffer_.remove(0, nl + 1);
        nl = rxBuffer_.indexOf('\n');
        if (line.isEmpty()) {
            continue;
        }
        QJsonParseError perr{};
        const QJsonDocument doc = QJsonDocument::fromJson(line, &perr);
        if (perr.error != QJsonParseError::NoError || !doc.isObject()) {
            continue;  // a malformed frame is dropped, never thrown
        }
        dispatchFrame(doc.object());
    }
}

void RpcConnection::dispatchFrame(const QJsonObject &frame) {
    const QJsonValue idVal = frame.value("id");
    const bool isResponse = frame.contains("result") || frame.contains("error");

    if (idVal.isDouble() && isResponse) {
        const qint64 id = static_cast<qint64>(idVal.toDouble());
        if (id == kHelloId) {
            if (frame.contains("error")) {
                socket_->abort();  // version mismatch or refused — bounce and retry
                return;
            }
            sendRaw(
                kSubscribeId, QString::fromLatin1(method::kSessionSubscribe),
                QJsonObject{
                    {"events", QJsonArray{event::kTaskAdded, event::kTaskRemoved, event::kTaskState,
                                          event::kTaskProgress, event::kSpeedGlobal, event::kNotify,
                                          event::kSettingsChanged, event::kGrabberProgress}}});
            return;
        }
        if (id == kSubscribeId) {
            if (frame.contains("error")) {
                socket_->abort();
                return;
            }
            backoffMs_ = kMinBackoffMs;
            setState(kStateConnected);
            return;
        }
        const auto it = pendingTags_.constFind(id);
        if (it != pendingTags_.cend()) {
            const quint64 tag = it.value();
            pendingTags_.erase(it);
            emit callCompleted(tag, frame);
        }
        return;
    }

    const QString methodName = frame.value("method").toString();
    if (!methodName.isEmpty()) {
        emit notificationReceived(methodName, frame.value("params").toObject());
    }
}

void RpcConnection::sendRaw(qint64 rpcId, const QString &methodName, const QJsonObject &params) {
    const QJsonObject req{{"jsonrpc", "2.0"},
                          {"id", static_cast<double>(rpcId)},
                          {"method", methodName},
                          {"params", params}};
    QByteArray line = QJsonDocument(req).toJson(QJsonDocument::Compact);
    line += '\n';
    socket_->write(line);
}

void RpcConnection::setState(int state) {
    if (state_ == state) {
        return;
    }
    state_ = state;
    emit stateChanged(state);
}

}  // namespace velox::gui::rpc