/*!
  \page ktexttemplate-for-app-devs
  \title KTextTemplate for application developers

  Integrating KTextTemplate into applications is very simple. This page describes
  \list
  \li How to render a Template with a Context
  \li How to load Templates
  \li How to extend the syntax of KTextTemplate
  \li Patterns of use of KTextTemplate
  \endlist

  If you are not already familiar with Django template syntax and structure, start with \l {KTextTemplate for theme artists}. If you are already familiar with Django, you might find \l {Differences between Django and KTextTemplate} informative.

  \section1 Rendering Templates

  \section2 Creating Templates

  Rendering templates is very easy in application code. A single Template may be rendered multiple times with different Context objects.

  \code
    auto engine = new KTextTemplate::Engine( this );
    auto t = engine->newTemplate("My name is {{ name }}.", "my_template_name");
    QVariantHash mapping;
    mapping.insert("name", "Grainne");
    KTextTemplate::Context c(mapping);

    t->render(&c); // Returns "My name is Grainne."

    mapping.insert("name", "Henry");
    c = KTextTemplate::Context(mapping);

    t->render(&c); // Returns "My name is Henry."
  \endcode

  Usually, applications do not create a Template directly, but instead use a KTextTemplate::Engine to load external files. This allows artists to define the template without needing to recompile.

  \code
    auto t = engine->loadByName("template.html");

    t->render(&c)
  \endcode

  \section2 Variables

  A Context object maps a string to another object for reference in the template. String keys in the Context object are available as variables in the Template, and can be used with the \c variable syntax or inside \c control tags. In the above example, we mapped the string \c "name" to the string \c "Grainne" and then to the string \c "Henry". We can create more than just string mappings though.

  \code
    mapping.insert("myint", 6); // Can insert ints
    mapping.insert("mydouble", 6.5); // Can insert doubles
    mapping.insert("mybool", false); // Can insert bools

    QVariantList mylist{"Ingrid", 3};
    mapping.insert("mylist", mylist); // Can insert QVariantList

    QVariantHash myhash;
    myhash.insert("James", "Artist");
    myhash.insert("Kiera", "Dreamer");
    mapping.insert("myhash", myhash); // Can insert QVariantHash

    QObject *obj = getObj();
    auto objVar = QVariant::fromValue(obj);
    mapping.insert("myobject", objVar); // Can insert QObject*
  \endcode

  It is additionally possible to insert any type of object or any container (not just QVariantHash and QVariantList) into the Context.
  See \l {Generic type and template support}.

  \section1 Extending KTextTemplate

  KTextTemplate has 5 extension points.
  \list
  \li Custom object variables
  \li Generic types and containers
  \li Filters
  \li Tags
  \li Loaders
  \endlist

  \section2 Custom objects

  Instances of QObject* can be inserted into templates. The recommended way to insert custom objects into templates is to create QObject wrappers for your objects. As QObject is introspectable, this will allow lookups to work in a way you define.

  \note If you are already familiar with Django you will know that creating wrappers is not necessary in Django. That is because python objects are already fully introspectable.

  \code
    #include "myperson.h"

    class PersonWrapper : public QObject
    {
      Q_OBJECT
      Q_PROPERTY(QString name READ name)
    public:
      PersonWrapper(const QString &name, int age);

      QString name() const;

      int age() const;

      QString clear();

    };

    ...

    auto linda = new PersonWrapper("Linda", 21);

    mapping.insert("person", linda);

    ...

    The name is {{ person.name }} and age is {{ person.age }}.

    // Will be rendered as
    // The name is Linda and age is .
  \endcode

  Note that the \c 'name' of \c PersonWrapper is accessible in the template, but the \c 'age' is not. Note also that rendering fails silently if the method can not be found. Only methods which have a corresponding \c Q_PROPERTY declaration are accessible from templates. To make \c age accessible in the template, we would need to add

  \code
    Q_PROPERTY(int age READ age)
  \endcode

  to the class. Note also that those methods are \c const. Rendering a template should never change an object it is rendering. Always make sure the READ properties of your wrapper objects are \c const. It is also possible to lookup dynamic properties of \c {QObject}s. In the case of dynamic properties, the property name must be UTF-8 encoded.

  If you already have \c {QObject}s in your application which would be suitable for use in templates, you only need to add some \c Q_PROPERTY entries to the classes to make them accessible to KTextTemplate.

  \note If you are familiar with Django you may be aware of the \c alters_data attribute for methods. This method of using wrappers and \c const is the equivalent to the \c alters_data attribute. You the wrapper writer choose the properties which will be accessible from the templates and makes them \c const, so there's no need to mark other methods as \c alters_data.

  For most uses of KTextTemplate, this is enough to get make an application themable easily and quickly. For more advanced usage, see \l {Extending the template system}. For some example uses of KTextTemplate, see \l {Examples of KTextTemplate use}.

  \section2 Custom Object Properties

  The broad introspection features of Qt5 are relied upon by KTextTemplate via the \c Q_PROPERTY macro.  Most types used with that macro may be accessed in %KTextTemplate templates without further code.

  We can define a Home type like this:

  \code
    class Home : public QObject
    {
        Q_OBJECT
        Q_PROPERTY(int houseNumber READ houseNumber)
        Q_PROPERTY(QString streetName READ streetName)
        Q_PROPERTY(QString city READ city)
    public:
        // ...
    };
  \endcode

  And we can use it in a \c Q_PROPERTY macro in our \c PersonWrapper type:

  \code
    class PersonWrapper : public QObject
    {
      Q_OBJECT
      Q_PROPERTY(QString name READ name)
      Q_PROPERTY(Home* home READ home)
    public:
      PersonWrapper(const QString &name, int age, Home *home);

      Home* home() const;

      // ...
    }
  \endcode

  And then use it in a template:

  \code
    <h1>{{ person.name }}</h1>
    House number: {{ person.home.houseNumber }}
    Street: {{ person.home.streetName }}
  \endcode

  Using containers such as QList and QSharedPointer with the <tt>Q_PROPERTY</tt> macro is also possible.

  \code
    class PersonWrapper : public QObject
    {
      Q_OBJECT
      Q_PROPERTY(QString name READ name)
      Q_PROPERTY(QList<PersonWrapper*> friends READ friends)
    public:
      PersonWrapper(const QString &name, int age, Home *home);

      QList<PersonWrapper> friends() const { return m_friends; }
      void setFriends(const QList<PersonWrapper*> friends) { m_friends = friends; }

      // ...

    private:
      QList<PersonWrapper*> m_friends;
    };
  \endcode

  Classes which do not derive from QObject, but which are decorated with the \c Q_GADGET and \c Q_PROPERTY macros may also be used as expected.

  \section2 Generic Variables

  An alternative to writing wrapper QObject classes with \c Q_PROPERTY macros is to use the KTextTemplate::MetaType system to provide introspection
  for any type or any container. This subject is treated in detail in \l {Generic type and template support}.

  \section2 Enumerators

  KTextTemplate has built-in support for enumerators which use the \c Q_ENUMS macro.

  \code
  class MyClass : public QObject
  {
    Q_OBJECT
    Q_ENUMS(PersonName)
    Q_PROPERTY(PersonName personName READ personName)
  public:

    enum PersonName
    {
      Mike,
      Natalie,
      Oliver,
      Patrica = 9
      Quentin
    };

    MyClass(QObject *parent = 0 );

    PersonName personName() const { return Quentin; }

  };

  ...

  {
    QObject *object = new MyClass(this);
    context.insert("myObj", object);
    t->render(context);
  }
  \endcode

  The enums can be used and accessed in various ways. See QMetaEnum for details.

  \code
    Oliver is value {{ myObj.Oliver }}.
    // Output: "Oliver is value 2".

    ...

    Oliver key is {{ myObj.Oliver.key }}.
    // Output: "Oliver key is Oliver".

    ...

    Oliver value is {{ myObj.Oliver.value }}.
    // Output: "Oliver value is 2".

    ...

    Oliver scope is {{ myObj.Oliver.scope }}.
    // Output: "Oliver scope is MyClass".

    ...

    Oliver scope is {{ myObj.Oliver.name }}.
    // Output: "Oliver scope is PersonName".

    ...

    Patrica is value {{ myObj.Patrica }}.
    // Output: "Patrica is value 9".

    ...

    PersonName has {{ myObj.PersonName.keyCount }} items.
    // Output: "PersonName has 5 items".

    ...

    Second item is {{ myObj.PersonName.1 }}.
    // Output: "Second item is 1".

    ...

    Second item is {{ myObj.PersonName.1.key }}.
    // Output: "Second item is Natalie".

    ...

    Fourth item is {{ myObj.PersonName.3 }}.
    // Output: "Fourth item is 9".

    ...

    Fourth item is {{ myObj.PersonName.3.key }}.
    // Output: "Fourth item is Patrica".

    ...

    The personName property is {{ myObj.personName }}.
    // Output: "The personName property is 10".

    ...

    The personName property is {{ myObj.personName.key }}.
    // Output: "The personName property is Quentin".

    ...

    The personName type is {{ myObj.personName.scope }}.
    // Output: "The personName type is PersonName".

    ...

    The personName is {% with myObj.personName as var %}{{ var }}, {{ var.key }}{% endwith %}.
    // Output: "The personName is 10, Quentin".

    ...

    The enum is {% with myObj.PersonName as enum %}{{ enum.3 }}, {{ enum.4 }}, {{ enum.4.key }}{% endwith %}.
    // Output: "The enum is 9, 10, Quentin".

    ...

    The enum is {% for enum in myObj.PersonName %}{{ enum }} : {{ enum.key }}, {% endfor %}.
    // Output: "The enum 0 : Mike, 1 : Natalie, 2 : Oliver, 9 : Patrica, 10 : Quentin, ".

    ...

    The enum is {% for enum in myObj.PersonName %}
                    {% ifequal enum Oliver %}**{{ enum }} : {{ enum.key }}**
                    {% else %}{{ enum }} : {{ enum.key }},
                    {% endifequal %}
                {% endfor %}.
    // Output: "The enum 0 : Mike, 1 : Natalie, **2 : Oliver**, 9 : Patrica, 10 : Quentin, ".

    ...

    The enum is {% for enum in myObj.PersonName %}
                    {% ifequal enum myObj.personName %}**{{ enum }} : {{ enum.key }}**
                    {% else %}{{ enum }} : {{ enum.key }},
                    {% endifequal %}
                {% endfor %}.
    // Output: "The enum 0 : Mike, 1 : Natalie, 2 : Oliver, 9 : Patrica, **10 : Quentin**, ".
  \endcode

  Enumerators in the Qt namespaces are also supported.

  \code
    AlignRight value is {{ Qt.AlignRight }}.
    // Output: "AlignRight value is 2".

    ...

    AlignRight key is {{ Qt.AlignRight.key }}.
    // Output: "AlignRight value is AlignRight".

    ...

    AlignRight scope is {{ Qt.AlignRight.scope }}.
    // Output: "AlignRight scope is Qt".

    ...

    AlignRight name is {{ Qt.AlignRight.name }}.
    // Output: "AlignRight scope is Alignment".

    ...

    {% ifequal myObj.alignment Qt.AlignRight %}RightAligned{% else %}Not RightAligned{% endifequal %}.
    // Output: "RightAligned". or "Not RightAligned", depending on the value of myObj.alignment.

    ...
  \endcode

*/