kde-playground/kdepimlibs/akonadi/item.h

/*
    Copyright (c) 2006 Volker Krause <vkrause@kde.org>
                  2007 Till Adam <adam@kde.org>

    This library is free software; you can redistribute it and/or modify it
    under the terms of the GNU Library General Public License as published by
    the Free Software Foundation; either version 2 of the License, or (at your
    option) any later version.

    This library is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
    License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to the
    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    02110-1301, USA.
*/

#ifndef AKONADI_ITEM_H
#define AKONADI_ITEM_H

#include "akonadi_export.h"

#include <akonadi/entity.h>
#include <akonadi/exception.h>
#include <akonadi/tag.h>
#include <akonadi/collection.h>
#include "itempayloadinternals_p.h"

#include <QtCore/QByteArray>
#include <QtCore/QMetaType>
#include <QtCore/QSet>

#include <boost/static_assert.hpp>
#include <boost/type_traits/is_pointer.hpp>
#include <boost/utility/enable_if.hpp>

#include <typeinfo>
#include <memory>

class KUrl;

template <typename T>
#include <QVector>

namespace Akonadi {

class ItemPrivate;

/**
 * @short Represents a PIM item stored in Akonadi storage.
 *
 * A PIM item consists of one or more parts, allowing a fine-grained access on its
 * content where needed (eg. mail envelope, mail body and attachments).
 *
 * There is also a namespace (prefix) for special parts which are local to Akonadi.
 * These parts, prefixed by "akonadi-", will never be fetched in the resource.
 * They are useful for local extensions like agents which might want to add meta data
 * to items in order to handle them but the meta data should not be stored back to the
 * resource.
 *
 * This class is implicitly shared.
 *
 * <h4>Payload</h4>
 *
 * This class contains, beside some type-agnostic information (flags, revision),
 * zero or more payload objects representing its actual data. Which objects these actually
 * are depends on the mimetype of the item and the corresponding serializer plugin(s).
 *
 * Technically the only restriction on payload objects is that they have to be copyable.
 * For safety reasons, pointer payloads are forbidden as well though, as the
 * ownership would not be clear. In this case, usage of a shared pointer is
 * recommended (such as boost::shared_ptr or QSharedPointer).
 *
 * Using a shared pointer is also required in case the payload is a polymorphic
 * type. For supported shared pointer types implicit casting is provided when possible.
 *
 * When using a value-based class as payload, it is recommended to use one that does
 * support implicit sharing as setting and retrieving a payload as well as copying
 * an Akonadi::Item object imply copying of the payload object.
 *
 * Since KDE 4.6, Item supports multiple payload types per mime type,
 * and will automatically convert between them using the serialiser
 * plugins (which is slow). It also supports mixing shared pointer
 * types, e.g. inserting a boost::shared_ptr<Foo> and extracting a
 * QSharedPointer<Foo>. Since the two shared pointer types cannot
 * share ownership of the same object, the payload class @c T needs to
 * provide a @c clone() method with the usual signature, ie.
 *
 * @code
 * virtual T * T::clone() const
 * @endcode
 *
 * If the class that does not have a @c clone() method, asking for an
 * incompatible shared pointer will throw a PayloadException.
 *
 * Since using different shared pointer types and different payload
 * types for the same mimetype incurs slow conversions (between
 * payload types) and cloning (between shared pointer types), as well
 * as manifold memory usage (results of conversions are cached inside
 * the Item, and only destroyed when a new payload is set by the user
 * of the class), you want to restrict yourself to just one type and
 * one shared pointer type. This mechanism was mainly introduced for
 * backwards compatibility (e.g., putting in a
 * boost::shared_ptr<KCal::Incidence> and extracting a
 * QSharedPointer<KCalCore::Incidence>), so it is not optimized for
 * performance.
 *
 * The availability of a payload of a specific type can be checked using hasPayload(),
 * payloads can be retrieved by using payload() and set by using setPayload(). Refer
 * to the documentation of those methods for more details.
 *
 * @author Volker Krause <vkrause@kde.org>, Till Adam <adam@kde.org>, Marc Mutz <mutz@kde.org>
 */
class AKONADI_EXPORT Item : public Entity
{
public:
    /**
     * Describes a list of items.
     */
    typedef QList<Item> List;

    /**
     * Describes a flag name.
     */
    typedef QByteArray Flag;

    /**
     * Describes a set of flag names.
     */
    typedef QSet<QByteArray> Flags;

    /**
     * Describes the part name that is used to fetch the
     * full payload of an item.
     */
    static const char *FullPayload;

    /**
     * Creates a new item.
     */
    Item();

    /**
     * Creates a new item with the given unique @p id.
     */
    explicit Item(Id id);

    /**
     * Creates a new item with the given mime type.
     *
     * @param mimeType The mime type of the item.
     */
    explicit Item(const QString &mimeType);

    /**
     * Creates a new item from an @p other item.
     */
    Item(const Item &other);

    /**
     * Destroys the item.
     */
    ~Item();

    /**
     * Creates an item from the given @p url.
     */
    static Item fromUrl(const KUrl &url);

    /**
     * Returns all flags of this item.
     */
    Flags flags() const;

    /**
     * Returns the timestamp of the last modification of this item.
     * @since 4.2
     */
    QDateTime modificationTime() const;

    /**
     * Sets the timestamp of the last modification of this item.
     * @param datetime the modification time to set
     * @note Do not modify this value from within an application,
     * it is updated automatically by the revision checking functions.
     * @since 4.2
     */
    void setModificationTime(const QDateTime &datetime);

    /**
     * Returns whether the flag with the given @p name is
     * set in the item.
     */
    bool hasFlag(const QByteArray &name) const;

    /**
     * Sets the flag with the given @p name in the item.
     */
    void setFlag(const QByteArray &name);

    /**
     * Removes the flag with the given @p name from the item.
     */
    void clearFlag(const QByteArray &name);

    /**
     * Overwrites all flags of the item by the given @p flags.
     */
    void setFlags(const Flags &flags);

    /**
     * Removes all flags from the item.
     */
    void clearFlags();

    void setTags(const Tag::List &list);

    void setTag(const Tag &tag);

    Tag::List tags() const;

    bool hasTag(const Tag &tag) const;

    void clearTag(const Tag &tag);

    void clearTags();

    /**
     * Sets the payload based on the canonical representation normally
     * used for data of this mime type.
     *
     * @param data The encoded data.
     * @see fullPayloadData
     */
    void setPayloadFromData(const QByteArray &data);

    /**
     * Returns the full payload in its canonical representation, e.g. the
     * binary or textual format usually used for data with this mime type.
     * This is useful when communicating with non-Akonadi application by
     * e.g. drag&drop, copy&paste or stored files.
     */
    QByteArray payloadData() const;

    /**
     * Returns the list of loaded payload parts. This is not necessarily
     * identical to all parts in the cache or to all available parts on the backend.
     */
    QSet<QByteArray> loadedPayloadParts() const;

    /**
     * Marks that the payload shall be cleared from the cache when this
     * item is passed to an ItemModifyJob the next time.
     * This will trigger a refetch of the payload from the backend when the
     * item is accessed afterwards. Only resources should have a need for
     * this functionality.
     *
     * @since 4.5
     */
    void clearPayload();

    /**
     * Sets the @p revision number of the item.
     * @param revision the revision number to set
     * @note Do not modify this value from within an application,
     * it is updated automatically by the revision checking functions.
     */
    void setRevision(int revision);

    /**
     * Returns the revision number of the item.
     */
    int revision() const;

    /**
     * Returns the unique identifier of the collection this item is stored in. There is only
     * a single such collection, although the item can be linked into arbitrary many
     * virtual collections.
     * Calling this method makes sense only after running an ItemFetchJob on the item.
     * @returns the collection ID if it is known, -1 otherwise.
     * @since 4.3
     */
    Entity::Id storageCollectionId() const;

    /**
     * Set the size of the item in bytes.
     * @param size the size of the item in bytes
     * @since 4.2
     */
    void setSize(qint64 size);

    /**
     * Returns the size of the items in bytes.
     *
     * @since 4.2
     */
    qint64 size() const;

    /**
     * Sets the mime type of the item to @p mimeType.
     */
    void setMimeType(const QString &mimeType);

    /**
     * Returns the mime type of the item.
     */
    QString mimeType() const;

    /**
     * Sets the @p gid of the entity.
     *
     * @since 4.12
     */
    void setGid(const QString &gid);

    /**
     * Returns the gid of the entity.
     *
     * @since 4.12
     */
    QString gid() const;

    /**
     * Sets the virtual @p collections that this item is linked into.
     *
     * @note Note that changing this value makes no effect on what collections
     * this item is linked to. To link or unlink an item to/from a virtual
     * collection, use LinkJob and UnlinkJob.
     *
     * @since 4.14
     */
    void setVirtualReferences(const Collection::List &collections);

    /**
     * Lists virtual collections that this item is linked to.
     *
     * @note This value is populated only when this item was retrieved by
     * ItemFetchJob with fetchVirtualReferences set to true in ItemFetchScope,
     * otherwise this list is always empty.
     *
     * @since 4.14
     */
    Collection::List virtualReferences() const;

    /**
     * Returns a list of metatype-ids, describing the different
     * variants of payload that are currently contained in this item.
     *
     * The result is always sorted (increasing ids).
     */
    QVector<int> availablePayloadMetaTypeIds() const;

    /**
     * Sets the payload object of this PIM item.
     *
     * @param p The payload object. Must be copyable and must not be a pointer,
     * will cause a compilation failure otherwise. Using a type that can be copied
     * fast (such as implicitly shared classes) is recommended.
     * If the payload type is polymorphic and you intend to set and retrieve payload
     * objects with mismatching but castable types, make sure to use a supported
     * shared pointer implementation (currently boost::shared_ptr and QSharedPointer)
     * and make sure there is a specialization of Akonadi::super_trait for your class.
     */
    template <typename T> void setPayload(const T &p);
    //@cond PRIVATE
    template <typename T> void setPayload(T *p);
    template <typename T> void setPayload(std::auto_ptr<T> p);
    //@endcond

    /**
     * Returns the payload object of this PIM item. This method will only succeed if either
     * you requested the exact same payload type that was put in or the payload uses a
     * supported shared pointer type (currently boost::shared_ptr and QSharedPointer), and
     * is castable to the requested type. For this to work there needs to be a specialization
     * of Akonadi::super_trait of the used classes.
     *
     * If a mismatching or non-castable payload type is requested, an Akonadi::PayloadException
     * is thrown. Therefore it is generally recommended to guard calls to payload() with a
     * corresponding hasPayload() call.
     *
     * Trying to retrieve a pointer type will fail to compile.
     */
    template <typename T> T payload() const;

    /**
     * Returns whether the item has a payload object.
     */
    bool hasPayload() const;

    /**
     * Returns whether the item has a payload of type @c T.
     * This method will only return @c true if either you requested the exact same payload type
     * that was put in or the payload uses a supported shared pointer type (currently boost::shared_ptr
     * and QSharedPointer), and is castable to the requested type. For this to work there needs
     * to be a specialization of Akonadi::super_trait of the used classes.
     *
     * Trying to retrieve a pointer type will fail to compile.
     */
    template <typename T> bool hasPayload() const;

    /**
     * Describes the type of url which is returned in url().
     */
    enum UrlType {
        UrlShort = 0,         ///< A short url which contains the identifier only (default)
        UrlWithMimeType = 1   ///< A url with identifier and mimetype
    };

    /**
     * Returns the url of the item.
     */
    KUrl url(UrlType type = UrlShort) const;

    /**
     * Returns the parts available for this item.
     *
     * The returned set refers to parts available on the akonadi server or remotely,
     * but does not include the loadedPayloadParts() of this item.
     *
     * @since 4.4
     */
    QSet<QByteArray> availablePayloadParts() const;

    /**
     * Returns the parts available for this item in the cache. The list might be a subset
     * of the actual parts in cache, as it contains only the requested parts. See @see ItemFetchJob and
     * @see ItemFetchScope
     *
     * The returned set refers to parts available on the akonadi server.
     *
     * @since 4.11
     */
    QSet<QByteArray> cachedPayloadParts() const;

    /**
     * Applies the parts of Item @p other to this item.
     * Any parts or attributes available in other, will be applied to this item,
     * and the payload parts of other will be inserted into this item, overwriting
     * any existing parts with the same part name.
     *
     * If there is an ItemSerialzerPluginV2 for the type, the merge method in that plugin is
     * used to perform the merge. If only an ItemSerialzerPlugin class is found, or the merge
     * method of the -V2 plugin is not implemented, the merge is performed with multiple deserializations
     * of the payload.
     * @param other the item to get values from
     * @since 4.4
     */
    void apply(const Item &other);

    /**
     * Registers \a T as a legacy type for mime type \a mimeType.
     *
     * This is required information for Item to return the correct
     * type from payload() when clients have not been recompiled to
     * use the new code.
     * @param mimeType the mimeType to register
     * @since 4.6
     */
    template <typename T> static void addToLegacyMapping(const QString &mimeType);
    void setCachedPayloadParts(const QSet<QByteArray> &cachedParts);

private:
    //@cond PRIVATE
    friend class ItemCreateJob;
    friend class ItemModifyJob;
    friend class ItemModifyJobPrivate;
    friend class ItemSync;
    friend class ProtocolHelper;
    PayloadBase *payloadBase() const;
    void setPayloadBase(PayloadBase *p);
    PayloadBase *payloadBaseV2(int sharedPointerId, int metaTypeId) const;
    //std::auto_ptr<PayloadBase> takePayloadBase( int sharedPointerId, int metaTypeId );
    void setPayloadBaseV2(int sharedPointerId, int metaTypeId, std::auto_ptr<PayloadBase> p);
    void addPayloadBaseVariant(int sharedPointerId, int metaTypeId, std::auto_ptr<PayloadBase> p) const;
    static void addToLegacyMappingImpl(const QString &mimeType, int sharedPointerId, int metaTypeId, std::auto_ptr<PayloadBase> p);

    /**
     * Try to ensure that we have a variant of the payload for metatype id @a mtid.
     * @return @c true if a type exists or could be created through conversion, @c false otherwise.
     */
    bool ensureMetaTypeId(int mtid) const;

    template <typename T>
    typename boost::enable_if_c<Internal::PayloadTrait<T>::isPolymorphic, void>::type
    setPayloadImpl(const T &p, const int * /*disambiguate*/ = 0);
    template <typename T>
    typename boost::disable_if_c<Internal::PayloadTrait<T>::isPolymorphic, void>::type
    setPayloadImpl(const T &p);

    template <typename T>
    typename boost::enable_if_c<Internal::PayloadTrait<T>::isPolymorphic, T>::type
    payloadImpl(const int * /*disambiguate*/ = 0) const;
    template <typename T>
    typename boost::disable_if_c<Internal::PayloadTrait<T>::isPolymorphic, T>::type
    payloadImpl() const;

    template <typename T>
    typename boost::enable_if_c<Internal::PayloadTrait<T>::isPolymorphic, bool>::type
    hasPayloadImpl(const int * /*disambiguate*/ = 0) const;
    template <typename T>
    typename boost::disable_if_c<Internal::PayloadTrait<T>::isPolymorphic, bool>::type
    hasPayloadImpl() const;

    template <typename T>
    typename boost::enable_if<Internal::is_shared_pointer<T>, bool>::type
    tryToClone(T *ret, const int * /*disambiguate*/ = 0) const;
    template <typename T>
    typename boost::disable_if<Internal::is_shared_pointer<T>, bool>::type
    tryToClone(T *) const;

    /**
     * Set the collection ID to where the item is stored in. Should be set only by the ItemFetchJob.
     * @param collectionId the unique identifier of the collection where this item is stored in.
     * @since 4.3
     */
    void setStorageCollectionId(Entity::Id collectionId);

#if 0
    /**
     * Helper function for non-template throwing of PayloadException.
     */
    QString payloadExceptionText(int spid, int mtid) const;

    /**
     * Non-template throwing of PayloadException.
     * Needs to be inline, otherwise catch (Akonadi::PayloadException)
     * won't work (only catch (Akonadi::Exception))
     */
    inline void throwPayloadException(int spid, int mtid) const {
        throw PayloadException(payloadExceptionText(spid, mtid));
    }
#else
    void throwPayloadException(int spid, int mtid) const;
#endif
    //@endcond

    AKONADI_DECLARE_PRIVATE(Item)
};

template <typename T>
T Item::payload() const
{
    BOOST_STATIC_ASSERT(!boost::is_pointer<T>::value);

    if (!hasPayload()) {
        throwPayloadException(-1, -1);
    }

    return payloadImpl<T>();
}

template <typename T>
typename boost::enable_if_c<Internal::PayloadTrait<T>::isPolymorphic, T>::type
Item::payloadImpl(const int *) const
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((PayloadType::isPolymorphic));

    typedef typename Internal::get_hierarchy_root<T>::type Root_T;
    typedef Internal::PayloadTrait<Root_T> RootType;
    BOOST_STATIC_ASSERT((!RootType::isPolymorphic));   // prevent endless recursion

    return PayloadType::castFrom(payloadImpl<Root_T>());
}

template <typename T>
typename boost::disable_if_c<Internal::PayloadTrait<T>::isPolymorphic, T>::type
Item::payloadImpl() const
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((!PayloadType::isPolymorphic));

    const int metaTypeId = PayloadType::elementMetaTypeId();

    // make sure that we have a payload format represented by 'metaTypeId':
    if (!ensureMetaTypeId(metaTypeId)) {
        throwPayloadException(PayloadType::sharedPointerId, metaTypeId);
    }

    // Check whether we have the exact payload
    // (metatype id and shared pointer type match)
    if (const Payload<T> *const p = Internal::payload_cast<T>(payloadBaseV2(PayloadType::sharedPointerId, metaTypeId))) {
        return p->payload;
    }

    T ret;
    if (!tryToClone<T>(&ret)) {
        throwPayloadException(PayloadType::sharedPointerId, metaTypeId);
    }
    return ret;
}

template <typename T>
typename boost::enable_if<Internal::is_shared_pointer<T>, bool>::type
Item::tryToClone(T *ret, const int *) const
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((!PayloadType::isPolymorphic));

    const int metaTypeId = PayloadType::elementMetaTypeId();

    // Check whether we have the same payload in 'the other
    // shared pointer' (### make it recurse, trying to find one, but
    // don't introduce infinite recursion):
    typedef typename Internal::shared_pointer_traits<T>::next_shared_ptr NewT;
    typedef Internal::PayloadTrait<NewT> NewPayloadType;

    if (const Payload<NewT> *const p = Internal::payload_cast<NewT>(payloadBaseV2(NewPayloadType::sharedPointerId, metaTypeId))) {
        // If found, attempt to make a clone (required the payload to provide virtual T * T::clone() const)
        const T nt = PayloadType::clone(p->payload);
        if (!PayloadType::isNull(nt)) {
            // if clone succeeded, add the clone to the Item:
            std::auto_ptr<PayloadBase> npb(new Payload<T>(nt));
            addPayloadBaseVariant(PayloadType::sharedPointerId, metaTypeId, npb);
            // and return it
            if (ret) {
                *ret = nt;
            }
            return true;
        }
    }

    return false;
}

template <typename T>
typename boost::disable_if<Internal::is_shared_pointer<T>, bool>::type
Item::tryToClone(T *) const
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((!PayloadType::isPolymorphic));

    return false;
}

template <typename T>
bool Item::hasPayload() const
{
    BOOST_STATIC_ASSERT(!boost::is_pointer<T>::value);
    return hasPayload() && hasPayloadImpl<T>();
}

template <typename T>
typename boost::enable_if_c<Internal::PayloadTrait<T>::isPolymorphic, bool>::type
Item::hasPayloadImpl(const int *) const
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((PayloadType::isPolymorphic));

    typedef typename Internal::get_hierarchy_root<T>::type Root_T;
    typedef Internal::PayloadTrait<Root_T> RootType;
    BOOST_STATIC_ASSERT((!RootType::isPolymorphic));   // prevent endless recursion

    try {
        return hasPayloadImpl<Root_T>()
               && PayloadType::canCastFrom(payload<Root_T>());
    } catch (const Akonadi::PayloadException &) {
        return false;
    }
}

template <typename T>
typename boost::disable_if_c<Internal::PayloadTrait<T>::isPolymorphic, bool>::type
Item::hasPayloadImpl() const
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((!PayloadType::isPolymorphic));

    const int metaTypeId = PayloadType::elementMetaTypeId();

    // make sure that we have a payload format represented by 'metaTypeId':
    if (!ensureMetaTypeId(metaTypeId)) {
        return false;
    }

    // Check whether we have the exact payload
    // (metatype id and shared pointer type match)
    if (const Payload<T> *const p = Internal::payload_cast<T>(payloadBaseV2(PayloadType::sharedPointerId, metaTypeId))) {
        return true;
    }

    return tryToClone<T>(0);
}

template <typename T>
void Item::setPayload(const T &p)
{
    BOOST_STATIC_ASSERT((!boost::is_pointer<T>::value));
    setPayloadImpl(p);
}

template <typename T>
typename boost::enable_if_c<Internal::PayloadTrait<T>::isPolymorphic>::type
Item::setPayloadImpl(const T &p, const int *)
{
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((PayloadType::isPolymorphic));

    typedef typename Internal::get_hierarchy_root<T>::type Root_T;
    typedef Internal::PayloadTrait<Root_T> RootType;
    BOOST_STATIC_ASSERT((!RootType::isPolymorphic));   // prevent endless recursion

    setPayloadImpl<Root_T>(p);
}

template <typename T>
typename boost::disable_if_c<Internal::PayloadTrait<T>::isPolymorphic>::type
Item::setPayloadImpl(const T &p)
{
    typedef Internal::PayloadTrait<T> PayloadType;
    std::auto_ptr<PayloadBase> pb(new Payload<T>(p));
    setPayloadBaseV2(PayloadType::sharedPointerId,
                     PayloadType::elementMetaTypeId(),
                     pb);
}

template <typename T>
void Item::setPayload(T *p)
{
    p->You_MUST_NOT_use_a_pointer_as_payload;
}

template <typename T>
void Item::setPayload(std::auto_ptr<T> p)
{
    p.Nice_try_but_a_std_auto_ptr_is_not_allowed_as_payload_either;
}

template <typename T>
void Item::addToLegacyMapping(const QString &mimeType) {
    typedef Internal::PayloadTrait<T> PayloadType;
    BOOST_STATIC_ASSERT((!PayloadType::isPolymorphic));
    std::auto_ptr<PayloadBase> p(new Payload<T>);
    addToLegacyMappingImpl(mimeType, PayloadType::sharedPointerId, PayloadType::elementMetaTypeId(), p);
}

}

Q_DECLARE_METATYPE(Akonadi::Item)
Q_DECLARE_METATYPE(Akonadi::Item::List)

#endif