// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page qtprotobuf-index.html
    \title Qt Protobuf
    \ingroup frameworks-technologies

    The Qt Protobuf \l {The qtprotobufgen Tool}{generator plugin} generates
    Qt-based classes from \c{.proto} files. You can use the classes to
    serialize and deserialize their associated protobuf messages.

    \section1 Overview

    \section2 What are protocol buffers?
    Protocol buffers are a language-neutral, platform-neutral, and extensible
    mechanism for serializing structured data, which is compact and easy
    to use:
    \list
        \li A user defines the structure of data in \c{.proto} files.
        \li Proto compiler is invoked at build time on \c{.proto} files to
            generate code in various programming languages.
    \endlist
    The provided format is suitable for network traffic or long-term data
    storage.

    \section2 Which problems do protocol buffers solve?
    Protocol buffers provide a serialization format for typed and structured data
    packets up to a few megabytes in size. It allows for the extension with new
    information without invalidating existing data or requiring code to be updated.
    For more information, see
    \l {https://protobuf.dev/}{Protocol Buffers Overview}.

    \section2 Benefits of using Qt Protobuf
    You can use a Protocol buffers mechanism in any Qt-based project:
    \list
        \li Without the need to call a protocol buffer compiler explicitly.
        \li Without manually integrating generated code into the project tree.
        \li To access the serialization and deserialization API.
        \li For integrated properties mechanism for generated protobuf messages.
        \li For integrated gRPC-client support, see \l {Qt GRPC}{Qt GRPC module}.
        \li For integrated \l{Qt Protobuf QML Types} {QML-types} support for
            generated protobuf messages.
        \li For using enabled \l {Protobuf Qt Core Types Module} {Qt Core} and
            \l {Protobuf Qt GUI types module} {Qt GUI} types as a part
            of *.proto schema.
    \endlist

    \section1 Using the Module
    Google protocol buffers provide a generator called \c protoc that
    supports extensions. \l {The qtprotobufgen Tool} is an extension
    for \c protoc and requires that you install \c protoc on your host system.
    For more information about the installation, see
    \l {https://grpc.io/docs/protoc-installation/}{Protoc Installation}.

    \section3
    \list
        \li Example of installation for Linux, using \e {apt}:
            \badcode
                apt install -y protobuf-compiler
                protoc --version  # Ensure compiler version is 3+
            \endcode
        \li \l {Example of installation for Windows using vcpkg}
    \endlist

    \section2 QML API
    The QML types of the module are available through the QML and QML_URI
    options in the \l{qt_add_protobuf} macro.
    The import name is equal to the \c.proto package name or defined by
    QML_URI option in the \l{qt_add_protobuf} macro.
    To use the types, add the following import statement to your .qml file:
    \code
        import my.proto.package.uri
    \endcode

    \section2 C++ API

    \include {module-use.qdocinc} {using the c++ api}

    \section3 Building with CMake

    \include {module-use.qdocinc} {building with cmake} {Protobuf}

    \section1 Articles and Guides
    \list
        \li \l {CMake Commands in Qt6 Protobuf}
        \li \l {Protobuf Qt Core Types Module} {Protobuf Qt Core Types}
        \li \l {Protobuf Qt GUI Types Module} {Protobuf Qt GUI Types}
        \li \l {Qt Protobuf Well-Known Types C++ Classes} {Qt Protobuf Well-Known types}
    \endlist

    \section1 References
    \list
        \li \l {Qt Protobuf C++ Classes}{Qt Protobuf C++ Classes}
        \li \l {Qt Protobuf QML Types}
    \endlist

    \section1 Examples
    \list
        \li \l {Qt Protobuf Examples}
    \endlist

    \section1 Licenses and Attributions

    The Qt Protobuf module is available under commercial licenses from \l{The Qt Company}.
    In addition, it is available under free software licenses:
    The \l{GNU Lesser General Public License, version 3}, or
    the \l{GNU General Public License, version 2}, or
    the \l{GNU General Public License, version 3}.
    See \l{Qt Licensing} for further details.

    Furthermore, the \c qtprotobufgen tool in Qt \QtVersion may contain third
    party modules under the following permissive licenses:

    \generatelist{groupsbymodule attributions-qtprotobuf-tools}
*/

/*!
    \module QtProtobuf
    \title Qt Protobuf C++ Classes
    \qtcmakepackage Protobuf
    \since 6.5
    \brief Provides protocol buffers support in Qt.
*/

/*!
    \group qtprotobuf-examples
    \title Qt Protobuf Examples
    \brief A collection describes existing QML-types support for \l {Qt Protobuf}

    These examples demonstrate how to generate code using the protobuf schema
    and use it in your projects.
*/

/*!
    \page qtprotobuf-installation-windows-vcpkg.html
    \title Example of installation for Windows using vcpkg
    \brief Installing instructions for Protobuf and \gRPC on Windows.

    You can install \c Protobuf and \c \gRPC packages on Windows using
    \e vcpkg.
    \note As an alternative solution, you can build \c Protobuf and \c \gRPC
    packages manually. Build instructions can be found for
    \l {https://github.com/protocolbuffers/protobuf/blob/main/cmake/README.md#windows-builds}{Protobuf}
    and \l{https://github.com/grpc/grpc/blob/v1.60.0/BUILDING.md#windows}{gRPC}
    respectively.

    Windows installation prerequisites:
    \list
        \li \l {https://vcpkg.io/en/getting-started.html}
            {The vcpkg package manager}
        \li \l {https://visualstudio.microsoft.com/vs/features/cplusplus/}
               {Microsoft Visual C++ compiler}
        \li \l {Get and Install Qt}
            {Qt 6.6 or later, including \e {Additional libraries}:
            \l {Qt Protobuf} and \l {Qt GRPC}}
    \endlist

    The \c vcpkg is a cross-platform C/C++ package manager.
    You can use the \c vcpkg for \c Protobuf, \c \gRPC and its dependencies
    installation:
    \badcode
        .\vcpkg.exe install protobuf protobuf:x64-windows
        .\vcpkg.exe install grpc:x64-windows
    \endcode
    \note We recommend using Manifest mode. This mode uses declarative JSON files
    to describe metadata about the project. Manifest files are required to have
    the vcpkg.json name.

    Finally, you can build and execute Qt-based projects with
    \c Protobuf and \c \gRPC support.
    For instance, run \l {Magic 8 Ball} from your installed version
    of Qt.
    The example requires both packages to be installed, since \c {Magic 8 Ball}
    uses native C++ source code generator plugin for the server part
    of application.
    Following steps are required to start \c {Magic 8 Ball} example:
    \list
        \li Find \l {Magic 8 Ball} in \c Examples section:
            \image qt-creator.webp
        \li Choose MSVC-based building kit from Qt-creator configuration
            settings:
            \image msvc-kit.webp
        \li Add the paths to the installed \c Protobuf and \c \gRPC packages
            to the \c CMAKE_PREFIX_PATH environment variable inside
            \c {Initial Configuration} settings block:
            \image path-env-variable.webp
        \li Build and Run.
    \endlist
*/

/*!
    \page qtprotobuf-qml-types.html
    \title Qt Protobuf QML Types
    \brief A collection of examples for \l {Qt Protobuf}

    With the \l{The qtprotobufgen Tool}{generator plugin}, you can register
    protobuf messages in the QML. To register the type, use the
    \c QML and \c QML_URI generation keys. See API details in
    \l{qt_add_protobuf}{qt_add_protobuf} command and
    API usage example \l{QML extended protobuf example}{QML extended protobuf}.

    Registered protobuf messages are available in the QML,
    like built-in \l{Q_GADGET} types. The registration is done via the QML
    module.

    \section1 Using protobuf messages in QML
    Use the \l{The qtprotobufgen Tool}{generator plugin} to generate libraries
    of protobuf messages that you can access from Qt Quick applications. The
    \l{CMake Commands in Qt6 Protobuf}{Qt Protobuf CMake API} has respective
    options that control the QML module creation.

    For example, you have the \c userdb.proto protobuf schema that contains the
    \c User message:
    \badcode
        syntax = "proto3";

        package userdb;

        message User {
            enum Type {
                Admin = 0;
                Manager = 1;
                Account = 2;
                Director = 3;
            }
            Type type = 1;
            string name = 2;
            string email = 3;
        }
    \endcode

    To expose the \c User message in QML, use the protobuf schema and the
    \l{qt_add_protobuf} command with the \c QML argument:
    \badcode
        qt_add_executable(appuserdb
            ...
        )

        qt_add_qml_module(appuserdb
            URI userdb
            VERSION 1.0
            QML_FILES
                ...
            SOURCES
                ...
        )

        qt_add_protobuf(userdb_gen
            QML
            QML_URI "userdb.pb"
            PROTO_FILES
                userdb.proto
        )

        target_link_libraries(appuserdb PRIVATE userdb_gen)
    \endcode

    The \l{qt_add_protobuf} function will generate a library called
    \c userdb_gen, containing the protobuf messages from \c userdb.proto with
    QML support. To use the messages in QML, import the generated QML module
    using the URI specified in the \c QML_URI argument of the \c qt_add_protobuf
    call:
    \code
    import userdb.pb
    \endcode

    All protobuf messages are registered as \l{QML Value Types}. To use them in
    QML, define the \l{Property attributes}{property attribute} for some QML
    item:
    \code
        Window {
            id: userAddForm
            property user newUser
            ...
        }
    \endcode

    To change the \c type, \c name, or \c email fields of the \c newUser
    property, use QML signal callbacks. For example:
    \code
        TextField {
            id: userNameField
            onTextChanged: {
                userAddForm.newUser.name = userNameField.text
            }
        }
        ...
        TextField {
            id: userEmailField
            onTextChanged: {
                userAddForm.newUser.email = userEmailField.text
            }
        }
    \endcode

    The \c User.Type enum values are also accessible from QML. The below example
    shows how to create a \l ComboBox item using the enum values:
    \code
        ComboBox {
            id: userTypeField
            textRole: "key"
            model: ListModel {
                id: userTypeModel
                ListElement { key: "Admin"; value: User.Admin }
                ListElement { key: "Second"; value: User.Manager }
                ListElement { key: "Account"; value: User.Account }
                ListElement { key: "Director"; value: User.Director }
            }
            onActivated: function(index) {
                userAddForm.newUser.type = userTypeModel.get(index).value
            }
        }
    \endcode

    \section1 Integrating QML and C++

    C++ classes registered in QML may use the messages created in QML in both
    properties and invocable methods.

    The singleton QML object \c UserDBEngine exposes the \c lastAddedUser
    property and the invocable method \c addUser to QML:
    \code
        class UserDBEngine : public QObject
        {
            Q_OBJECT
            QML_ELEMENT
            QML_SINGLETON

            Q_PROPERTY(userdb::User lastAddedUser READ lastAddedUser WRITE setLastAddedUser NOTIFY lastAddedUserChanged FINAL)
        public:
            ...
            Q_INVOKABLE void addUser(const userdb::User &newUser);
            ...
        }
    \endcode

    The \c lastAddedUser property has the \c userdb::User type generated from
    the \c userdb.proto schema from the previous section. The invocable
    \c addUser method accepts constant reference to an object of
    \c userdb::User type. Both property and method can be used from QML:
    \code
        Button {
            text: "Add"
            onClicked: {
                // Use the property created in the previous section
                UserDBEngine.addUser(userAddForm.newUser)
            }
        }
        ...
        Text {
            // The text will be updated automatically when lastAddedUser is changed
            text: "Last added user: " + UserDBEngine.lastAddedUser.name
        }
    \endcode

    \section1 Protobuf message duplicates
    You should avoid declaration of protobuf message duplicates in your
    \c *.proto files or do it wisely. If your application uses several identical
    protobuf message names declared inside different protobuf packages, they
    might contradict each other in auto-generated code.
    In the example below, two different proto packages, \c qtprotobufnamespace
    and \c qtprotobufnamespace1.nested, use the same proto message
    \c NestedFieldMessage.
    The file \c nested.proto:
    \badcode
        syntax = "proto3";

        package qtprotobufnamespace;
        import "externalpackage.proto";

        message NestedFieldMessage {
            sint32 testFieldInt = 1;
        }
    \endcode
    The file \c nestedspace1.proto:
    \badcode
        syntax = "proto3";

        package qtprotobufnamespace1.nested;

        message NestedFieldMessage {
            message NestedMessage {
                sint32 field = 1;
            }
            NestedMessage nested = 1;
        }
    \endcode
    In case there is no possibility to avoid name duplicates among
    packages, then put duplicated messages in different QML modules
    and use a <Qualifier> for each QML module import,
    see \l{Module (Namespace) Imports}.
    Below the example how to add protobuf packages into different
    QML modules:
    \badcode
        # qtprotobufnamespace QML module
        qt_add_protobuf(nestedtypes_qtprotobuf_qml
            PROTO_FILES
                nested.proto
            QML
            QML_URI
                qtprotobufnamespace
            OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/qt_protobuf_gen1"
        )

        ...

        # qtprotobufnamespace1.nested QML module
        qt_add_protobuf(nestedspace_qml
            PROTO_FILES
                nestedspace1.proto
            QML
            QML_URI
                qtprotobufnamespace1.nested
            OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/qt_protobuf_gen2"
        )
    \endcode
    The <Qualifier> usage example:
    \badcode
        import qtprotobufnamespace as NestedFieldMessages
        import qtprotobufnamespace1.nested as FieldMessages_Nested1

        ...

        property NestedFieldMessages.nestedFieldMessage fieldMsg1;
        property FieldMessages_Nested1.nestedFieldMessage fieldMsg2;
    \endcode
    \note The usage of duplicates will trigger a warning at compilation time.

    \section1 QML types duplicates
    If your application uses protobuf messages with names that
    are already reserved in QML as QML types, then the correct behavior
    cannot be guaranteed, and \c {Element is not creatable} error
    would be triggered. To prevent an overlapping of QML Types,
    use a <Qualifier> for QML module import, see
    \l{Module (Namespace) Imports}.
    For example, the following protobuf messages would be clashing
    with the \l Text and \l Item QML types when imported into the
    global namespace:
    \badcode
        syntax = "proto3";
        package test.example;

        message Text {
            string text = 1;
        }

        message Item {
            sint32 width = 1;
            sint32 height = 2;
        }
    \endcode
    Use the \l qt_add_protobuf macro with the \c QML option to
    enable QML types generation from the above protobuf messages.
    See the example below:
    \badcode
        qt_add_protobuf(example
            PROTO_FILES
                test.proto
            QML
            QML_URI
                test.example
        )
    \endcode
    Clashes with the QML types will be triggered if protobuf
    messages are imported into a global namespace after the QtQuick
    import. See the example below:
    \badcode
        import QtQuick
        import test.example

        Item {
           id: root
           ...
           property ProtobufMessages.item itemData
       }
    \endcode
    To avoid clashes with the QML types, use a \c <Qualifier>
    to import the generated QML module into a local namespace.
    See the example below:
    \badcode
        // No qualifier - global namespace
        import QtQuick
        // ProtobufMessages - a qualifier of local namespace.
        import test.example as ProtobufMessages

        Item {
            id: root
            ...
            property ProtobufMessages.item itemData
        }
    \endcode
    \section2 QML keywords handling
    Pay attention to the keywords that are reserved in QML or
    JavaScript context, but not reserved in *.proto context.
    Fields with names that are reserved by QML
    will be silently extended by \c _proto suffix by the
    \l {The qtprotobufgen Tool}{generator plugin}.
    For example, \c id, \c property, and \c import are reserved keywords.
    They will be replaced by \c id_proto, \c property_proto,
    \c import_proto:
    \badcode
        message MessageUpperCaseReserved {
            sint32 Import = 1;
            sint32 Property = 2;
            sint32 Id = 3;
        }
    \endcode
    Generated code output:
    \code
        Q_PROPERTY(QtProtobuf::sint32 import_proto READ import_proto ...)
        Q_PROPERTY(QtProtobuf::sint32 property_proto READ property_proto ...)
        Q_PROPERTY(QtProtobuf::sint32 id_proto READ id_proto ...)
    \endcode
    Also, enum values cannot begin with a lower case letter.
    The \l {The qtprotobufgen Tool}{generator plugin} will capitalize
    the first letter in code output. See the \c *.proto example below:
    \badcode
        enum LowerCaseEnum {
            enumValue0 = 0;
            enumValue1 = 1;
            enumValue2 = 2;
        }
    \endcode
    Generated code output:
    \code
        enum LowerCaseEnum {
            EnumValue0 = 0,
            EnumValue1 = 1,
            EnumValue2 = 2,
        };
        Q_ENUM(LowerCaseEnum)
    \endcode
    Also, enum fields cannot begin with an underscore symbol.
    Such fields will be generated as is, but will be undefined in
    the QML, unless the QML engine will allow registering
    them in the future. See the \c *.proto example below:
    \badcode
        enum UnderScoreEnum {
            _enumUnderscoreValue0 = 0;
            _EnumUnderscoreValue1 = 1;
        }
    \endcode
    Generated output:
    \code
        enum UnderScoreEnum {
            _enumUnderscoreValue0 = 0,
            _EnumUnderscoreValue1 = 1,
        };
        Q_ENUM(UnderScoreEnum)
    \endcode
    For more information about the QML properties syntax, check
    \l {Defining Property Attributes}.
*/
