qgsmaplayerref.h

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/***************************************************************************
  qgsmaplayerref.h
  --------------------------------------
  Date                 : January 2017
  Copyright            : (C) 2017 by Martin Dobias
  Email                : wonder dot sk at gmail dot com
 ***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/
 
#ifndef QGSMAPLAYERREF_H
#define QGSMAPLAYERREF_H
 
#define SIP_NO_FILE
 
#include <utility>
 
#include "qgsdataprovider.h"
#include "qgsmaplayer.h"
#include "qgsproject.h"
 
#include <QDomElement>
#include <QPointer>

template<typename TYPE>
struct _LayerRef
{

  enum MatchType
  {
    Name = 1 << 2, 
    Provider = 1 << 3, 
    Source = 1 << 4, 
    All = Provider | Source 
  };
 

  _LayerRef( TYPE *l = nullptr )
    : layer( l )
    , layerId( l ? l->id() : QString() )
    , source( l ? l->publicSource() : QString() )
    , name( l ? l->name() : QString() )
    , provider( l && l->dataProvider() ? l->dataProvider()->name() : QString() )
  {}

  _LayerRef( const QString &id, const QString &name = QString(), const QString &source = QString(), const QString &provider = QString() )
    : layer()
    , layerId( id )
    , source( source )
    , name( name )
    , provider( provider )
  {}

  void setLayer( TYPE *l )
  {
    layer = l;
    layerId = l ? l->id() : QString();
    source = l ? l->publicSource() : QString();
    name = l ? l->name() : QString();
    provider = l && l->dataProvider() ? l->dataProvider()->name() : QString();
  }

  bool operator==( const _LayerRef &other ) = delete;

  explicit operator bool() const
  {
    return static_cast< bool >( layer.data() );
  }

  TYPE *operator->() const
  {
    return layer.data();
  }

  TYPE *get() const
  {
    return layer.data();
  }

  QPointer<TYPE> layer;

  QString layerId;

  QString source;
  QString name;
  QString provider;

  bool layerMatchesSource( QgsMapLayer *layer ) const
  {
    if ( layer->publicSource() != source ||
         layer->name() != name )
      return false;
 
    if ( layer->providerType() != provider )
      return false;
 
    return true;
  }

  TYPE *resolve( const QgsProject *project )
  {
    if ( project && !layerId.isEmpty() )
    {
      if ( TYPE *l = qobject_cast<TYPE *>( project->mapLayer( layerId ) ) )
      {
        setLayer( l );
        return l;
      }
    }
    return nullptr;
  }
 
  bool layerMatchesWeakly( QgsMapLayer *layer, MatchType matchType = MatchType::All ) const
  {
    // First match the name
    if ( matchType & MatchType::Name && ( layer->name().isEmpty() || layer->name() != name ) )
    {
      return false;
    }
    else
    {
      // We have found a match by name, now check the other
      // criteria
      if ( matchType & MatchType::Provider && layer->providerType() != provider )
      {
        return false;
      }
      if ( matchType & MatchType::Source && layer->publicSource() != source )
      {
        return false;
      }
      // All tests passed
      return true;
    }
  }

  TYPE *resolveWeakly( const QgsProject *project, MatchType matchType = MatchType::All )
  {
    // first try matching by layer ID
    if ( resolve( project ) )
      return layer;
 
    if ( project )
    {
      QList<QgsMapLayer *> layers;
      // If matching by name ...
      if ( matchType & MatchType::Name )
      {
        if ( name.isEmpty() )
        {
          return nullptr;
        }
        layers = project->mapLayersByName( name );
      }
      else // ... we need all layers
      {
        layers = project->mapLayers().values();
      }
      for ( auto it = layers.constBegin(); it != layers.constEnd(); ++it )
      {
        if ( TYPE *tl = qobject_cast< TYPE *>( *it ) )
        {
          if ( layerMatchesWeakly( tl, matchType ) )
          {
            setLayer( tl );
            return tl;
          }
        }
      }
    }
    return nullptr;
  }

  TYPE *resolveByIdOrNameOnly( const QgsProject *project )
  {
    // first try by matching by layer ID, or weakly by source, name and provider
    if ( resolveWeakly( project ) )
      return layer;
 
    // fallback to checking by name only
    if ( project && !name.isEmpty() )
    {
      const QList<QgsMapLayer *> layers = project->mapLayersByName( name );
      for ( QgsMapLayer *l : layers )
      {
        if ( TYPE *tl = qobject_cast< TYPE *>( l ) )
        {
          setLayer( tl );
          return tl;
        }
      }
    }
    return nullptr;
  }

  bool readXml( const QDomElement &element, const QgsReadWriteContext &context )
  {
    Q_UNUSED( context )
 
    layerId = element.attribute( QStringLiteral( "id" ) );
    name = element.attribute( QStringLiteral( "name" ) );
    source = element.attribute( QStringLiteral( "source" ) );
    provider = element.attribute( QStringLiteral( "provider" ) );
    return true;
  }

  void writeXml( QDomElement &element, const QgsReadWriteContext &context ) const
  {
    Q_UNUSED( context )
 
    element.setAttribute( QStringLiteral( "id" ), layerId );
    element.setAttribute( QStringLiteral( "name" ), name );
    element.setAttribute( QStringLiteral( "source" ), source );
    element.setAttribute( QStringLiteral( "provider" ), provider );
  }
 
};
 
typedef _LayerRef<QgsMapLayer> QgsMapLayerRef;
 
#endif // QGSMAPLAYERREF_H