text: #include "expressionfilter.h"
  #include "qqmlsortfilterproxymodel.h"
  #include <QtQml>
  
  namespace qqsfpm {
  
  /*!
      \qmltype ExpressionFilter
      \inherits Filter
      \inqmlmodule SortFilterProxyModel
      \brief Filters row with a custom filtering
  
      An ExpressionFilter is a \l Filter allowing to implement custom filtering based on a javascript expression.
  */
  
  /*!
      \qmlproperty expression ExpressionFilter::expression
  
      An expression to implement custom filtering, it must evaluate to a boolean.
      It has the same syntax has a \l {http://doc.qt.io/qt-5/qtqml-syntax-propertybinding.html} {Property Binding} except it will be evaluated for each of the source model's rows.
      Rows that have their expression evaluating to \c true will be accepted by the model.
      Data for each row is exposed like for a delegate of a QML View.
  
      This expression is reevaluated for a row every time its model data changes.
      When an external property (not \c index or in \c model) the expression depends on changes, the expression is reevaluated for every row of the source model.
      To capture the properties the expression depends on, the expression is first executed with invalid data and each property access is detected by the QML engine.
      This means that if a property is not accessed because of a conditional, it won't be captured and the expression won't be reevaluted when this property changes.
  
      A workaround to this problem is to access all the properties the expressions depends unconditionally at the beggining of the expression.
  */
  const QQmlScriptString& ExpressionFilter::expression() const
  {
      return m_scriptString;
  }
  
  void ExpressionFilter::setExpression(const QQmlScriptString& scriptString)
  {
      if (m_scriptString == scriptString)
          return;
  
      m_scriptString = scriptString;
      updateExpression();
  
      Q_EMIT expressionChanged();
      invalidate();
  }
  
  void ExpressionFilter::proxyModelCompleted(const QQmlSortFilterProxyModel& proxyModel)
  {
      updateContext(proxyModel);
  }
  
  bool ExpressionFilter::filterRow(const QModelIndex& sourceIndex, const QQmlSortFilterProxyModel& proxyModel) const
  {
      if (!m_scriptString.isEmpty()) {
          QVariantMap modelMap;
          QHash<int, QByteArray> roles = proxyModel.roleNames();
  
          QQmlContext context(qmlContext(this));
          auto addToContext = [&] (const QString &name, const QVariant& value) {
              context.setContextProperty(name, value);
              modelMap.insert(name, value);
          };
  
          for (auto it = roles.cbegin(); it != roles.cend(); ++it)
              addToContext(it.value(), proxyModel.sourceData(sourceIndex, it.key()));
          addToContext("index", sourceIndex.row());
  
          context.setContextProperty("model", modelMap);
  
          QQmlExpression expression(m_scriptString, &context);
          QVariant variantResult = expression.evaluate();
  
          if (expression.hasError()) {
              qWarning() << expression.error();
              return true;
          }
          if (variantResult.canConvert<bool>()) {
              return variantResult.toBool();
          } else {
              qWarning("%s:%i:%i : Can't convert result to bool",
                       expression.sourceFile().toUtf8().data(),
                       expression.lineNumber(),
                       expression.columnNumber());
              return true;
          }
      }
      return true;
  }
  
  void ExpressionFilter::updateContext(const QQmlSortFilterProxyModel& proxyModel)
  {
      delete m_context;
      m_context = new QQmlContext(qmlContext(this), this);
      // what about roles changes ?
      QVariantMap modelMap;
  
      auto addToContext = [&] (const QString &name, const QVariant& value) {
          m_context->setContextProperty(name, value);
          modelMap.insert(name, value);
      };
  
      for (const QByteArray& roleName : proxyModel.roleNames().values())
          addToContext(roleName, QVariant());
  
      addToContext("index", -1);
  
      m_context->setContextProperty("model", modelMap);
      updateExpression();
  }
  
  void ExpressionFilter::updateExpression()
  {
      if (!m_context)
          return;
  
      delete m_expression;
      m_expression = new QQmlExpression(m_scriptString, m_context, 0, this);
      connect(m_expression, &QQmlExpression::valueChanged, this, &ExpressionFilter::invalidate);
      m_expression->setNotifyOnValueChanged(true);
      m_expression->evaluate();
  }
  
  }
  