/* -*- mode: c++; indent-tabs-mode: nil -*- */
/*
    QoreTypeSafeReferenceHelper.h

    Qore Programming Language

    Copyright (C) 2003 - 2023 Qore Technologies, s.r.o.

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.

    Note that the Qore library is released under a choice of three open-source
    licenses: MIT (as above), LGPL 2+, or GPL 2+; see README-LICENSE for more
    information.
*/

#ifndef _QORE_QORETYPESAFEREFERENCEHELPER_H

#define _QORE_QORETYPESAFEREFERENCEHELPER_H

//! helper class to manage variable references passed to functions and class methods, stack only, cannot be dynamically allocated
/**
    Takes care of safely accessing ReferenceNode objects, for example when they are passed
    as arguments to a builtin function or method.  Locks are automatically acquired in the constructor
    if necessary and released in the destructor.  The constructor could raise a Qore-language
    exception if there is a deadlock acquiring any locks to access the ReferenceNode's value
    as given by the lvalue expression, so the object should be checked for this state right
    after the constructor as in the following example:
    @code
    QoreValue p = get_param_value(args, 0);
    if (p.getType() == NT_REFERENCE) {
        const ReferenceNode *r = p.get<const ReferenceNode>();
        QoreTypeSafeReferenceHelper ref(r, xsink);
        // a deadlock exception occurred accessing the reference's value pointer
        if (!ref)
            return QoreValue();

        // more code to access the reference
    }
    @endcode
 */
class QoreTypeSafeReferenceHelper {
private:
    //! this function is not implemented; it is here as a private function in order to prohibit it from being used
    DLLLOCAL QoreTypeSafeReferenceHelper(const QoreTypeSafeReferenceHelper&);

    //! this function is not implemented; it is here as a private function in order to prohibit it from being used
    DLLLOCAL QoreTypeSafeReferenceHelper& operator=(const QoreTypeSafeReferenceHelper&);

    //! this function is not implemented; it is here as a private function in order to prohibit it from being used
    DLLLOCAL void *operator new(size_t);

    //! private implementation
    struct qore_type_safe_ref_helper_priv_t *priv;

public:
    //! initializes the object and tries to get the pointer to the pointer of the lvalue expression target
    /** @param ref the ReferenceNode to use
        @param xsink Qore-language exceptions raised will be added here (for example, a deadlock accessing the object)
    */
    DLLEXPORT QoreTypeSafeReferenceHelper(const ReferenceNode *ref, ExceptionSink *xsink);

    //! initializes the object and tries to get the pointer to the pointer of the lvalue expression target
    /** @param ref the ReferenceNode to use
        @param vl this argument is ignored in this deprecated version of the function
        @param xsink Qore-language exceptions raised will be added here (for example, a deadlock accessing the object)

        @deprecated the AutoVLock argument is ignored in this deprecated version
    */
    DLLEXPORT QoreTypeSafeReferenceHelper(const ReferenceNode *ref, AutoVLock &vl, ExceptionSink *xsink);

    //! destroys the object
    DLLEXPORT ~QoreTypeSafeReferenceHelper();

    //! returns true if the reference is valid, false if not
    /** false will only be returned if a Qore-language exception was raised in the constructor
        */
    DLLEXPORT operator bool() const;

    //! returns the type of the reference's value
    /** @return the type of the reference's value
        */
    DLLEXPORT qore_type_t getType() const;

    //! returns the type name of the reference's value
    /** @return the type name of the reference's value
        */
    DLLEXPORT const char* getTypeName() const;

    //! returns a pointer to the value with a unique reference count (so it can be updated in place), assumes the reference is valid and the lvalue holds a reference-counted AbstractQoreNode*, if not, this call will cause a segfault
    /** @param xsink required for the call to AbstractQoreNode::deref()
        @returns a pointer to the reference's value with a unique reference count (so it can be modified), or 0 if the value was 0 to start with or if a Qore-language exception was raised
        @note you must check that the reference is valid before calling this function
        @note take care to only call this function on types where the AbstractQoreNode::realCopy() function has a valid implementation (on all value types suitable for in-place modification this function has a valid implementation), as in debugging builds other types will abort(); in non-debugging builds this function will cause a segfault

        @code
        QoreTypeSafeReferenceHelper rh(ref, xsink);
        // if the reference is not valid, then return
        if (!rh)
            return;
        if (rh.getType() == NT_LIST) {
            // get the unique value
            QoreListNode* l = static_cast<QoreListNode*>(rh.getUnique(xsink));
            // if a Qore-language exception was raised, then return
            if (*xsink)
                return;
        }
        @endcode
    */
    DLLEXPORT AbstractQoreNode* getUnique(ExceptionSink *xsink);

    //! assigns a value to the reference, assumes the reference is valid
    /** @param val the value to assign (must be already referenced for the assignment)
        @return 0 if there was no error and the variable was assigned, -1 if a Qore-language exception occured dereferencing the current value, in this case no assignment was made and the reference count for val is dereferenced automatically by the QoreTypeSafeReferenceHelper object
        @note you must check that the reference is valid before calling this function
        @code
        QoreTypeSafeReferenceHelper rh(ref, xsink);
        // if the reference is not valid, then return
        if (!rh)
            return;
        // make the assignment (if the assignment fails, the value will be dereferenced automatically)
        rh.assign(val->refSelf());
        @endcode
    */
    DLLEXPORT int assign(QoreValue val);

    //! returns the reference's value
    /** @return the value of the lvalue reference
    */
    DLLEXPORT const QoreValue getValue() const;
};

#endif
