// $Id: IDataSymLink.hxx,v 1.6 2007/11/28 20:08:05 mcgrew Exp $
//
// The base class for Event Data.
//
#ifndef T_DATA_SYM_LINK_HXX
#define T_DATA_SYM_LINK_HXX

#include <iostream>

class TBrowser;

#include "IDatum.hxx"

namespace COMET {
    OA_EXCEPTION(EBadSymLink,EDatum);
    class IDataSymLink;
}

#define TDATA_SYM_LINK_TITLE "Link To"

/// The IDataSymLink class provides a way to reference a IDatum object in a
/// IData tree without having the IData object become the parent.  This is
/// conceptually similar to a symbolic link in a unix file system.
class COMET::IDataSymLink : public IDatum {
private:
    /// The datum which this is a link too.
    TString fLink;

public:
    /// A virtual function that can be used to have "special" Get<>
    /// behavior.  This is mostly used by the TDatumLink class so that
    /// it can have a weak reference to IDatum elsewhere in the
    /// hierarchy, and have a Get<> method that refers transparently to
    /// the linked object.  The GetThis() method should be used
    /// wherever the link indirection might be desired.  Notice that
    /// this will follow the link all the way to the real object (even
    /// if there are several links along the way.
    virtual const IDatum *GetThis(void) const {
        IHandle<IDatum> parent = GetParent<IDatum>();
        if (!parent) return NULL;
        // The name in fLink relative to the parent.
        IHandle<IDatum> link = parent->Get<IDatum>(fLink);
        if (!link) return NULL;
        return link->GetThis();
    };

    virtual IDatum *GetThis(void) {
        IHandle<IDatum> parent = GetParent<IDatum>();
        if (!parent) return NULL;
        // The name in fLink relative to the parent.
        IHandle<IDatum> link = parent->Get<IDatum>(fLink);
        if (!link) return NULL;
        return link->GetThis();
    };

public:
    IDataSymLink() : IDatum("",TDATA_SYM_LINK_TITLE) { };

    /// Create a new IDataSymLink.  A IDataSymLink inherits two fields from
    /// IDatum, "Name" and "Title".  The name is the handle that is
    /// used to find "this" in IData objects.  It can only contain
    /// alphanumeric characters (no "/" or spaces) and///should* be
    /// unique with in any level of the IData hierarchy.  For instance,
    /// to get a particular datum out of a IData object you use
    /// data->Get<TDatumClass>("thename").  The title is a discription
    /// of a particular type of datum.  As an example, the MC
    /// interaction data might be named "interaction" and titled "MC
    /// Interaction Data".  The default title is "Event Datum".
    explicit IDataSymLink(const char* name, const char *link = NULL) 
        : IDatum(name,TDATA_SYM_LINK_TITLE) {
        SetLink(link);
    };

    virtual ~IDataSymLink();

    /// Set the IDatum that is being linked.
    virtual void SetLink(const char* link) {
        if (link) fLink = link;
        else fLink = "";
    };

    /// Print the datum information.
    virtual void ls(Option_t* opt = "") const;

    /// Check if this link is to a browsable class.
    virtual Bool_t IsFolder(void) const;

    /// Call the browser for the linked class.
    virtual void Browse(TBrowser* b);

private:
    IDatum* RemoveDatum(IDatum*){
        MayNotUse("RemoveDatum");
        return NULL;
    }
    void InsertDatum(IDatum*){
        MayNotUse("InsertDatum");
    }
    IDatum* FindDatum(const char *){
        MayNotUse("FindDatum");
        return NULL;
    }

protected:
    ClassDef(IDataSymLink,2);
};
#endif