// userviewmodel.h
#ifndef USERVIEWMODEL_H
#define USERVIEWMODEL_H

#include <QObject>
#include <QQmlEngine>
#include <QStringListModel>

class UserViewModel : public QObject {
    Q_OBJECT
    QML_ELEMENT

    Q_PROPERTY(QString userName READ userName
               WRITE setUserName NOTIFY userNameChanged)
    Q_PROPERTY(QString email READ email
               WRITE setEmail NOTIFY emailChanged)
    Q_PROPERTY(bool isValid READ isValid NOTIFY validationChanged)
    Q_PROPERTY(QStringList userList READ userList NOTIFY userListChanged)
    Q_PROPERTY(QString errorMessage READ errorMessage NOTIFY errorMessageChanged)

public:
    explicit UserViewModel(QObject *parent = nullptr) : QObject(parent) {
        loadUsers();
    }

    QString userName() const { return m_userName; }
    QString email() const { return m_email; }
    bool isValid() const { return m_isValid; }
    QStringList userList() const { return m_userList; }
    QString errorMessage() const { return m_errorMessage; }

    void setUserName(const QString &name) {
        if (m_userName != name) {
            m_userName = name;
            emit userNameChanged();
            validate();
        }
    }

    void setEmail(const QString &email) {
        if (m_email != email) {
            m_email = email;
            emit emailChanged();
            validate();
        }
    }

    Q_INVOKABLE void addUser() {
        if (!m_isValid) return;

        // 业务逻辑
        m_userList.append(m_userName + " <" + m_email + ">");
        emit userListChanged();

        // 重置
        m_userName.clear();
        m_email.clear();
        emit userNameChanged();
        emit emailChanged();
        validate();
    }

    Q_INVOKABLE void removeUser(int index) {
        if (index >= 0 && index < m_userList.size()) {
            m_userList.removeAt(index);
            emit userListChanged();
        }
    }

signals:
    void userNameChanged();
    void emailChanged();
    void validationChanged();
    void userListChanged();
    void errorMessageChanged();

private:
    void validate() {
        bool valid = true;
        QString error;

        if (m_userName.trimmed().isEmpty()) {
            valid = false;
            error = "请输入姓名";
        } else if (!m_email.contains('@')) {
            valid = false;
            error = "邮箱格式无效";
        }

        if (m_isValid != valid) {
            m_isValid = valid;
            emit validationChanged();
        }
        if (m_errorMessage != error) {
            m_errorMessage = error;
            emit errorMessageChanged();
        }
    }

    void loadUsers() {
        m_userList = {"张三 <zhangsan@example.com>",
                      "李四 <lisi@example.com>"};
    }

    QString m_userName;
    QString m_email;
    bool m_isValid = false;
    QStringList m_userList;
    QString m_errorMessage;
};

#endif

// UserPage.qml
import QtQuick
import QtQuick.Controls
import QtQuick.Layouts
import MyApp

Page {
    UserViewModel { id: viewModel }

    ColumnLayout {
        anchors.fill: parent
        anchors.margins: 16
        spacing: 12

        Text {
            text: "添加用户"
            font.pixelSize: 20
            font.bold: true
        }

        TextField {
            id: nameField
            placeholderText: "姓名"
            text: viewModel.userName
            onTextChanged: viewModel.userName = text
            Layout.fillWidth: true
        }

        TextField {
            id: emailField
            placeholderText: "邮箱"
            text: viewModel.email
            onTextChanged: viewModel.email = text
            Layout.fillWidth: true
        }

        Text {
            text: viewModel.errorMessage
            color: "#e74c3c"
            visible: !viewModel.isValid
        }

        Button {
            text: "添加"
            enabled: viewModel.isValid
            onClicked: {
                viewModel.addUser();
                nameField.text = "";
                emailField.text = "";
            }
            Layout.fillWidth: true
        }

        ListView {
            Layout.fillWidth: true
            Layout.fillHeight: true
            model: viewModel.userList
            delegate: RowLayout {
                width: ListView.view.width
                Label {
                    text: modelData
                    Layout.fillWidth: true
                }
                Button {
                    text: "删除"
                    flat: true
                    onClicked: viewModel.removeUser(index)
                }
            }
        }
    }
}

// QML 延迟加载
StackView {
    id: stackView
}

// 使用 Loader 延迟加载
Loader {
    id: heavyComponent
    active: false
    sourceComponent: Component {
        HeavyVisualization { }
    }
}

Button {
    text: "加载可视化"
    onClicked: heavyComponent.active = true
}

// Qt Widgets 延迟加载
class MainWindow : public QMainWindow {
    void showSettings() {
        if (!m_settingsDialog) {
            m_settingsDialog = new SettingsDialog(this); // 首次使用时创建
        }
        m_settingsDialog->show();
    }
    SettingsDialog *m_settingsDialog = nullptr; // 延迟初始化
};

// 预编译查询（复用）
class UserRepository {
public:
    UserRepository() {
        // 预编译，后续调用只绑定参数
        m_insertQuery.prepare(
            "INSERT INTO users (name, email, age) VALUES (?, ?, ?)");
    }

    int create(const QString &name, const QString &email, int age) {
        m_insertQuery.bindValue(0, name);
        m_insertQuery.bindValue(1, email);
        m_insertQuery.bindValue(2, age);
        m_insertQuery.exec();
        return m_insertQuery.lastInsertId().toInt();
    }

private:
    QSqlQuery m_insertQuery;
};

// 批量插入使用事务
void batchInsert(const QStringList &names) {
    QSqlDatabase::database().transaction();
    QSqlQuery query;
    query.prepare("INSERT INTO users (name) VALUES (?)");
    for (const auto &name : names) {
        query.bindValue(0, name);
        query.exec();
    }
    QSqlDatabase::database().commit();
}

// ✅ 好的做法
class MainWindow : public QMainWindow {
    // parent 自动管理子控件生命周期
    auto *button = new QPushButton("Click", this);

    // deleteLater 安全删除
    QObject *obj = createWorker();
    connect(worker, &Worker::finished, obj, &QObject::deleteLater);

    // 非 QObject 使用智能指针
    auto config = std::make_unique<AppConfig>();
    auto data = QSharedPointer<DataModel>::create();
};

// ❌ 坏的做法
void badExample() {
    QWidget *w = new QWidget();     // 无 parent，泄漏！
    deleteLater(w);                  // 不要这样
    delete w;                        // 如果 w 有 pending 事件，崩溃！
}

/* GObject 引用计数 */
MyObject *obj = my_object_new();
g_object_ref(obj);    // 增加引用
g_object_unref(obj);  // 减少引用
g_object_unref(obj);  // 最后一次释放

/* GtkWindow 等由 GTK 管理 */
GtkWidget *window = gtk_window_new();  // 浮动引用
gtk_window_present(GTK_WINDOW(window)); // sink 浮动引用，GTK 接管

/* GBoxed 类型 */
gchar *str = g_strdup("Hello");
g_free(str);

GVariant *variant = g_variant_new_string("test");
g_variant_unref(variant);

// 源码中标记可翻译字符串
class MainWindow : public QMainWindow {
    void setupUI() {
        setWindowTitle(tr("我的应用 / My Application"));

        auto *fileMenu = menuBar()->addMenu(tr("文件(&F)"));
        fileMenu->addAction(tr("新建(&N)"));
        fileMenu->addAction(tr("打开(&O)"));

        auto *label = new QLabel(tr("欢迎, %1!").arg(m_userName));

        // 复数形式
        int count = 5;
        label->setText(tr("%n 个文件已选中", nullptr, count));
    }
};

// main.cpp 加载翻译
int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QTranslator translator;
    QString locale = QLocale::system().name();  // "zh_CN"
    if (translator.load("myapp_" + locale, ":/translations")) {
        app.installTranslator(&translator);
    }

    MainWindow w;
    w.show();
    return app.exec();
}

# CMakeLists.txt - 自动生成 .ts 文件
qt_add_translations(myapp
    TS_FILES myapp_zh_CN.ts myapp_en_US.ts
    SOURCES ${SOURCES}
)

"""Python 国际化 - 使用 gettext"""

import gettext
import locale

# 设置语言
lang = gettext.translation(
    'myapp',
    localedir='locales',
    languages=['zh_CN'],
    fallback=True
)
_ = lang.gettext

# 使用
print(_("Hello, World!"))
print(_("File saved successfully"))
print(_("Error: {}").format("connection failed"))

/* GTK 国际化使用 gettext */
#include <glib/gi18n.h>

/* 初始化 */
bindtextdomain(GETTEXT_PACKAGE, LOCALE_DIR);
bind_textdomain_codeset(GETTEXT_PACKAGE, "UTF-8");
textdomain(GETTEXT_PACKAGE);

/* 使用 */
gtk_button_set_label(button, _("_Save"));
gtk_label_set_text(label, _("Welcome, %s!"), username);

# meson.build - i18n 支持
i18n = import('i18n')

# 编译翻译文件
i18n.gettext(meson.project_name(),
    preset: 'glib',
    locales: ['zh_CN', 'en_US']
)

// 1. 信号-槽错误通知
class NetworkService : public QObject {
    Q_OBJECT
signals:
    void requestFinished(const QJsonDocument &result);
    void requestFailed(const QString &error, int code);
};

// 2. Result 模式
template<typename T>
class Result {
public:
    static Result<T> success(T value) { return Result(value, "", true); }
    static Result<T> failure(const QString &error) { return Result(T(), error, false); }

    bool isSuccess() const { return m_success; }
    T value() const { return m_value; }
    QString error() const { return m_error; }

private:
    Result(T value, QString error, bool success)
        : m_value(std::move(value)), m_error(std::move(error)), m_success(success) {}
    T m_value;
    QString m_error;
    bool m_success;
};

// 使用
Result<int> parseInt(const QString &str) {
    bool ok;
    int value = str.toInt(&ok);
    if (ok) return Result<int>::success(value);
    return Result<int>::failure("Invalid number: " + str);
}

/* GError 模式 */
GError *error = NULL;
gboolean success = my_operation(&error);
if (!success) {
    g_printerr("Error: %s (code: %d)\n", error->message, error->code);
    g_error_free(error);
}

/* GtkAlertDialog 显示错误 */
static void show_error_dialog(GtkWindow *parent, const char *message) {
    GtkAlertDialog *dialog = gtk_alert_dialog_new("错误 / Error");
    gtk_alert_dialog_set_detail(dialog, message);
    const char *buttons[] = {"确定", NULL};
    gtk_alert_dialog_set_buttons(dialog, buttons);
    gtk_alert_dialog_choose(dialog, parent, NULL, NULL, NULL);
}