/**
  * @RDE_HEADER@
  * Class ResultWatcherBase, ResultWatcher
  * $Id$
  * $HeadURL$
  * $Author$
  */
#pragma once

// Own
#include "advanced_symbology_export.h"
#include "symbol_dictionary_types.h"
#include <SymbologyImpl/advanced_symbology_logging.h>

// Qt
#include <QObject>


//----------------------------------------------------------------------------
namespace AdvancedSymbology
{

//----------------------------------------------------------------------------
// - ResultWatcherBase (containing the Q_OBJECT for signal/slot)
// - ResultWatcher (containing template)
//----------------------------------------------------------------------------

//----------------------------------------------------------------------------
// ResultWatcherBase (containing the Q_OBJECT for signal/slot)
//----------------------------------------------------------------------------
/**
 * @brief The ResultWatcherBase class is a simple base class of ResultWatcher
 * and contain the signal resultReady, since a template class can`t.
 */
class ADVANCED_SYMBOLOGY_EXPORT ResultWatcherBase : public QObject
{
  Q_OBJECT

public:
  ///< Constructor
  explicit ResultWatcherBase(QObject *parent = nullptr)
    : QObject(parent)
  {}

  ///< Destructor
  ~ResultWatcherBase() = default;


Q_SIGNALS:
  /// Signal emits when result is ready
  void resultReady();

protected Q_SLOTS:
  void onResultReadyInternal()
  {
    // to avoid emitting signal twice:

    if (! m_alreadyEmitted)
      emit resultReady();
    m_alreadyEmitted = true;
  }

protected:
  bool m_alreadyEmitted = false;
};


//----------------------------------------------------------------------------
// ResultWatcher (containing template)
//----------------------------------------------------------------------------

/**
 * @brief The ResultWatcher class takes a result and will emit resultReady exactly one time.
 *
 * \section secResultWatcherExample Using the ResultWatcher
 * Here is an example of using the ResultWatcher
 *
 * \code
 *  AdvancedSymbology::SymbolDictionary &dict = AdvancedSymbology::SymbolDictionary::dictionary(AdvancedSymbology::MIL2525D);
 *
 *  AdvancedSymbology::SymbolResultWatcher symbolResultWatcher;
 *
 *  // FIRST connect:
 *  connect(&symbolResultWatcher, &AdvancedSymbology::SymbolResultWatcher::resultReady, this, [](){
 *
 *   QSharedPointer<AdvancedSymbology::SymbolResult> symResult = symbolResultWatcher.symbolResult();
 *   if (! symResult)
 *     return;  // should NEVER happen! (Which object should have triggered the signal???)
 *
 *   if (this->m_targetObject)
 *   {
 *     this->m_targetObject->setImage(symResult->symbolImage().image());
 *   }
 *  });
 *
 *  // SECOND setResult (starting the asynchronous operation)
 *  symbolResultWatcher.setSymbolResult( dict.findSymbol("mySidc") );
 * \endcode
 *
 * There is an convenience class: SymbolResultWatcherComboxBox
 *
 * @note
 * Template classes can not contain signals why this is moved to the base class ResultWatcherBase.
 *
 */
template <typename RESULT_TYPE>
class ResultWatcher : public ResultWatcherBase
{
public:
  ///< Constructor
  explicit ResultWatcher(QObject *parent = nullptr)
    : ResultWatcherBase(parent)
  {}

  ///< Destructor
  virtual ~ResultWatcher() = default;

  bool resultIsValid() const
  {
    return ! m_result.isNull();
  }

  void cancel()
  {
    m_result.clear();
  }

protected:
  QSharedPointer<RESULT_TYPE> result() const
  {
    return m_result;
  }

  void setResult(const QSharedPointer<RESULT_TYPE> &result)
  {
    // 2017-11-13, N.Thoden :
    // With rev 36928 the SymbolResult of two identical request (identical SymbolDataToRender)
    // will shared ONE SymbolResult!
    // This szenario happens while showing a snapshot.
    // So we have to disconnect explicitly:

    // make sure, that we won`t be called by the 'old' object:
    // so disconnect:
    if (m_result)
      m_result->disconnect(this);
    // : 2017-11-13, N.Thoden


    m_result = result;
    m_alreadyEmitted = false;

    if (m_result)
    {
      // Handle race condition:

      // 1. connect
      connect(m_result.data(), &RESULT_TYPE::resultReadyInternal, this, &ResultWatcher::onResultReadyInternal);

      // 2. maybe result was ready before?
      if (m_result->isResultReady())
        onResultReadyInternal();
    }
  }

  QSharedPointer<RESULT_TYPE> m_result;
};


} // namespace AdvancedSymbology