/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \example simpletextviewer
    \ingroup examples-qtassistant
    \title Simple Text Viewer Example

    \brief Using \QA as a customized help viewer for your application.

    \image simpletextviewer-example.png

    This is done in two stages. Firstly, documentation is created and \QA
    is customized; secondly, the functionality to launch and control
    \QA is added to the application.

    The Simple Text Viewer application lets the user select and view
    existing files.

    The application provides its own custom documentation that is
    available from the \gui Help menu in the main window's menu bar
    or by clicking the \gui Help button in the application's find file
    dialog.

    The example consists of four classes:

    \list
        \li \c Assistant provides functionality to launch \QA.
        \li \c MainWindow is the main application window.
        \li \c FindFileDialog allows the user to search for
           files using wildcard matching.
        \li \c TextEdit provides a rich text browser that makes
           sure that images referenced in HTML documents are
           displayed properly.
    \endlist

    \note We will only comment on the parts of the implementation
    that are relevant to the main issue, that is making Qt Assistant
    act as a customized help viewer for our Simple Text Viewer
    application.

    \section1 Creating Documentation and Customizing \QA

    How to create the actual documentation in the form of HTML pages is
    not in the scope of this example. In general, HTML pages can either
    be written by hand or generated with the help of documentation tools
    like qdoc or Doxygen. For the purposes of this example we assume that
    the HTML files have already been created. So, the only thing that
    remains to be done is to tell \QA how to structure and display the
    help information.

    \section2 Organizing Documentation for \QA

    Plain HTML files only contain text or documentation about specific topics,
    but they usually include no information about how several HTML documents
    relate to each other or in which order they are supposed to be read.
    What is missing is a table of contents along with an index to access
    certain help contents quickly, without having to browse through a lot
    of documents in order to find a piece of information.

    To organize the documentation and make it available for \QA, we have
    to create a Qt help project (.qhp) file. The first and most important
    part of the project file is the definition of the namespace. The namespace
    has to be unique and will be the first part of the page URL in \QA.
    In addition, we have to set a virtual folder which acts as a common
    folder for documentation sets. This means, that two documentation sets
    identified by two different namespaces can cross reference HTML files
    since those files are in one big virtual folder. However, for this
    example, we'll only have one documentation set available, so the
    virtual folder name and functionality are not important.

    \code
    <?xml version="1.0" encoding="UTF-8"?>
    <QtHelpProject version="1.0">
      <namespace>org.qt-project.examples.simpletextviewer</namespace>
      <virtualFolder>doc</virtualFolder>
    \endcode

    The next step is to define the filter section. A filter section
    contains the table of contents, indices and a complete list of
    all documentation files, and can have any number of filter attributes
    assigned to it. A filter attribute is an ordinary string which can
    be freely chosen. Later in \QA, users can then define a custom
    filter referencing those attributes. If the attributes of a filter
    section match the attributes of the custom filter the documentation
    will be shown, otherwise \QA will hide the documentation.

    Again, since we'll only have one documentation set, we do not need
    the filtering functionality of \QA and can therefore skip the
    filter attributes.

    Now, we build up the table of contents. An item in the table is
    defined by the \c section tag which contains the attributes for the
    item title as well as link to the actual page. Section tags can be
    nested infinitely, but for practical reasons it is not recommended
    to nest them deeper than three or four levels. For our example we
    want to use the following outline for the table of contents:

    \list
    \li Simple Text Viewer
      \list
      \li Find File
        \list
        \li File Dialog
        \li Wildcard Matching
        \li Browse
        \endlist
      \li Open File
      \endlist
    \endlist

    In the help project file, the outline is represented by:

    \code
     <filterSection>
       <toc>
         <section title="Simple Text Viewer" ref="index.html">
           <section title="Find File" ref="./findfile.html">
             <section title="File Dialog" ref="./filedialog.html"></section>
             <section title="Wildcard Matching" ref="./wildcardmatching.html"></section>
             <section title="Browse" ref="./browse.html"></section>
           </section>
           <section title="Open File" ref="./openfile.html"></section>
         </section>
       </toc>
    \endcode

    After the table of contents is defined, we will list all index keywords:

    \code
        <keywords>
          <keyword name="Display" ref="./index.html"/>
          <keyword name="Rich text" ref="./index.html"/>
          <keyword name="Plain text" ref="./index.html"/>
          <keyword name="Find" ref="./findfile.html"/>
          <keyword name="File menu" ref="./findfile.html"/>
          <keyword name="File name" ref="./filedialog.html"/>
          <keyword name="File dialog" ref="./filedialog.html"/>
          <keyword name="File globbing" ref="./wildcardmatching.html"/>
          <keyword name="Wildcard matching" ref="./wildcardmatching.html"/>
          <keyword name="Wildcard syntax" ref="./wildcardmatching.html"/>
          <keyword name="Browse" ref="./browse.html"/>
          <keyword name="Directory" ref="./browse.html"/>
          <keyword name="Open" ref="./openfile.html"/>
          <keyword name="Select" ref="./openfile.html"/>
        </keywords>
    \endcode

    As the last step, we have to list all files making up the documentation.
    An important point to note here is that all files have to listed, including
    image files, and even stylesheets if they are used.

    \code
        <files>
          <file>browse.html</file>
          <file>filedialog.html</file>
          <file>findfile.html</file>
          <file>index.html</file>
          <file>intro.html</file>
          <file>openfile.html</file>
          <file>wildcardmatching.html</file>
          <file>images/browse.png</file>
          <file>images/*.png</file>
        </files>
      </filterSection>
    </QtHelpProject>
    \endcode

    The help project file is now finished. If you want to see the resulting
    documentation in \QA, you have to generate a Qt compressed help file
    out of it and register it with the default help collection of \QA.

    \code
    qhelpgenerator simpletextviewer.qhp -o simpletextviewer.qch
    assistant -register simpletextviewer.qch
    \endcode

    If you start \QA now, you'll see the Simple Text Viewer documentation
    beside the Qt documentation. This is OK for testing purposes, but
    for the final version we want to only have the Simple Text Viewer
    documentation in \QA.

    \section2 Customizing \QA

    The easiest way to make \QA only display the Simple Text Viewer
    documentation is to create our own help collection file. A collection
    file is stored in a binary format, similar to the compressed help file,
    and generated from a help collection project file (*.qhcp). With
    the help of a collection file, we can customize the appearance and even
    some functionality offered by \QA.

    At first, we change the window title and icon. Instead of showing "\QA"
    it will show "Simple Text Viewer", so it is much clearer for the user
    that the help viewer actually belongs to our application.

    \code
    <?xml version="1.0" encoding="UTF-8"?>
    <QHelpCollectionProject version="1.0">
    <assistant>
        <title>Simple Text Viewer</title>
        <applicationIcon>images/handbook.png</applicationIcon>
        <cacheDirectory>QtProject/SimpleTextViewer</cacheDirectory>
    \endcode

    The \c cacheDirectory tag specifies a subdirectory of the users
    data directory (see the
    \l{Customizing Qt Assistant#Qt Help Collection Files}{Qt Help Collection Files})
    where the cache file for the full text search or the settings file will
    be stored.

    After this, we set the page displayed by \QA when launched for the very
    first time in its new configuration. The URL consists of the namespace
    and virtual folder defined in the Qt help project file, followed by the
    actual page file name.

    \code
        <startPage>qthelp://org.qt-project.examples.simpletextviewer/doc/index.html</startPage>
    \endcode

    Next, we alter the name of the "About" menu item to "About Simple
    Text Viewer". The contents of the \gui{About} dialog are also changed
    by specifying a file where the about text or icon is taken from.

    \code
        <aboutMenuText>
            <text>About Simple Text Viewer</text>
        </aboutMenuText>
        <aboutDialog>
            <file>about.txt</file>
            <icon>images/icon.png</icon>
        </aboutDialog>
    \endcode

    \QA offers the possibility to add or remove documentation via its
    preferences dialog. This functionality is helpful when using \QA
    as the central help viewer for more applications, but in our case
    we want to actually prevent the user from removing the documentation.
    So, we hide the \gui Documentation tab in the \gui Preferences dialog.

    Since the address bar is not really relevant in such a small
    documentation set we switch it off as well. By having just one filter
    section, without any filter attributes, we can also disable the filter
    functionality of \QA, which means that the filter page and the filter
    toolbar will not be available.

    \code
        <enableDocumentationManager>false</enableDocumentationManager>
        <enableAddressBar>false</enableAddressBar>
        <enableFilterFunctionality>false</enableFilterFunctionality>
    </assistant>
    \endcode

    For testing purposes, we already generated the compressed help file
    and registered it with \QA's default help collection. With the
    following lines we achieve the same result. The only and important
    difference is that we register the compressed help file, not in
    the default collection, but in our own collection file.

    \code
      <docFiles>
        <generate>
            <file>
                <input>simpletextviewer.qhp</input>
                <output>simpletextviewer.qch</output>
                </file>
            </generate>
        <register>
            <file>simpletextviewer.qch</file>
            </register>
        </docFiles>
    </QHelpCollectionProject>
    \endcode

    As the last step, we have to generate the binary collection file
    out of the help collection project file. This is done by running the
    \c qcollectiongenerator tool.

    \code
    qcollectiongenerator simpletextviewer.qhcp -o simpletextviewer.qhc
    \endcode

    To test all our customizations made to \QA, we add the collection
    file name to the command line:

    \code
    assistant -collectionFile simpletextviewer.qhc
    \endcode

    \section1 Controlling \QA via the Assistant Class

    We will first take a look at how to start and operate \QA from a
    remote application. For that purpose, we create a class called
    \c Assistant.

    This class provides a public function that is used to show pages
    of the documentation, and one private helper function to make sure
    that \QA is up and running.

    Launching \QA is done in the function \c startAssistant() by simply
    creating and starting a QProcess. If the process is already running,
    the function returns immediately. Otherwise, the process has
    to be set up and started.

    \snippet simpletextviewer/assistant.cpp 2

    To start the process we need the executable name of \QA as well as the
    command line arguments for running \QA in a customized mode. The
    executable name is a little bit tricky since it depends on the
    platform, but fortunately it is only different on \macos.

    The displayed documentation can be altered using the \c -collectionFile
    command line argument when launching \QA. When started without any options,
    \QA displays a default set of documentation. When Qt is installed,
    the default documentation set in \QA contains the Qt reference
    documentation as well as the tools that come with Qt, such as Qt
    Designer and \c qmake.

    In our example, we replace the default documentation set with our
    custom documentation by passing our application-specific collection
    file to the process's command line options.

    As the last argument, we add \c -enableRemoteControl, which makes \QA
    listen to its \c stdin channel for commands, such as those to display
    a certain page in the documentation.
    Then we start the process and wait until it is actually running. If,
    for some reason \QA cannot be started, \c startAssistant() will return
    false.

    The implementation for \c showDocumentation() is now straightforward.
    Firstly, we ensure that \QA is running, then we send the request to
    display the \a page via the \c stdin channel of the process. It is very
    important here that the command is terminated by the '\\0' character
    followed by an end of line token to flush the channel.

    \snippet simpletextviewer/assistant.cpp 1

    Finally, we make sure that \QA is terminated properly in the case that
    the application is shut down. The destructor of QProcess kills the
    process, meaning that the application has no possibility to do things
    like save user settings, which would result in corrupted settings files.
    To avoid this, we ask \QA to terminate in the destructor of the
    \c Assistant class.

    \snippet simpletextviewer/assistant.cpp 0

    \section1 MainWindow Class

    \image simpletextviewer-mainwindow.png

    The \c MainWindow class provides the main application window with
    two menus: the \gui File menu lets the user open and view an
    existing file, while the \gui Help menu provides information about
    the application and about Qt, and lets the user open \QA to
    display the application's documentation.

    To be able to access the help functionality, we initialize the
    \c Assistant object in the \c MainWindow's constructor.

    \snippet simpletextviewer/mainwindow.cpp 0
    \dots
    \snippet simpletextviewer/mainwindow.cpp 1

    Then we create all the actions for the Simple Text Viewer application.
    Of special interest is the \c assistantAct action accessible
    via the \key{F1} shortcut or the \gui Help > \gui {Help Contents} menu item.
    This action is connected to the \c showDocumentation() slot of
    the \c MainWindow class.

    \snippet simpletextviewer/mainwindow.cpp 4
    \dots
    \snippet simpletextviewer/mainwindow.cpp 5

    In the \c showDocumentation() slot, we call the \c showDocumentation()
    function of the \c Assistant class with the URL of home page of the
    documentation.

    \snippet simpletextviewer/mainwindow.cpp 3

    Finally, we must reimplement the protected QWidget::closeEvent()
    event handler to ensure that the application's \QA instance is
    properly closed before we terminate the application.

    \snippet simpletextviewer/mainwindow.cpp 2

    \section1 FindFileDialog Class

    \image simpletextviewer-findfiledialog.png

    The Simple Text Viewer application provides a find file dialog
    allowing the user to search for files using wildcard matching. The
    search is performed within the specified directory, and the user
    is given an option to browse the existing file system to find the
    relevant directory.

    In the constructor we save the references to the \c Assistant
    and \c QTextEdit objects passed as arguments. The \c Assistant
    object will be used in the \c FindFileDialog's \c help() slot,
    as we will see shortly, while the QTextEdit will be used in the
    dialog's \c openFile() slot to display the chosen file.

    \snippet simpletextviewer/findfiledialog.cpp 0
    \dots
    \snippet simpletextviewer/findfiledialog.cpp 1

    The most relevant member to observe in the \c FindFileDialog
    class is the private \c help() slot. The slot is connected to the
    dialog's \gui Help button, and brings the current \QA instance
    to the foreground with the documentation for the dialog by
    calling \c Assistant's \c showDocumentation() function.

    \snippet simpletextviewer/findfiledialog.cpp 2

    \section1 Summary

    In order to make \QA act as a customized help tool for
    your application, you must provide your application with a
    process that controls \QA in addition to a custom help collection
    file including Qt compressed help files.

    For  more information about the options and settings available to
    applications that use \QA as a custom help viewer, see
    \l{Customizing Qt Assistant}.
*/
