// ==========================================================================
//                 SeqAn - The Library for Sequence Analysis
// ==========================================================================
// Copyright (c) 2006-2018, Knut Reinert, FU Berlin
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
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//     * Neither the name of Knut Reinert or the FU Berlin nor the names of
//       its contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
// DAMAGE.
//
// ==========================================================================
// Author: Andreas Gogol-Döring <andreas.doering@mdc-berlin.de>
// TODO(holtgrew): Or is this by Dave?
// ==========================================================================
// Pointer-like data structure that helps with the management of volatile
// data, used in external string during swapping.  See class documentation
// for more details
// ==========================================================================

#ifndef SEQAN_BASIC_BASIC_VOLATILE_PTR_H_
#define SEQAN_BASIC_BASIC_VOLATILE_PTR_H_

namespace seqan {

// ============================================================================
// Forwards
// ============================================================================

// ============================================================================
// Tags, Classes, Enums
// ============================================================================

// TODO(holtgrew): Is volatile pointer the correct name?
// TODO(holtgrew): Metafunctions etc. missing.

/*!
 * @class VolatilePtr
 * @headerfile <seqan/basic.h>
 * @brief Helper data structure for handling volatile data.
 *
 * @signature template <typename T>
 *            class VolatilePtr;
 *
 * @tparam T The pointed-to type.
 *
 * Allows you to handle volatile data (used by ext. string during swapping).
 *
 * Imagine volatile pointers as nodes in an undirected graph.  When you assign one to another then they are connected.
 * All pointers in a connection component points to the same value.  By calling nukeCopies you can destroy
 * the component and set all pointers to <tt>NULL</tt>.
 */

template < typename Type >
struct VolatilePtr
{
    typedef VolatilePtr     Self_;
    typedef VolatilePtr*    SelfPtr_;
    typedef VolatilePtr&    SelfRef_;

    typedef Type&           reference;
    typedef const Type&     const_reference;
    typedef Type*           pointer;

    pointer         ptr;
    SelfPtr_        next;           // prev == NULL means this is the master node
    SelfPtr_        prev;           // prev == NULL means this is the master node

    VolatilePtr() {     // volatile pinters behave like normal pointers
        prev = this;    // and are not initialized (ptr) per default
        next = this;
    }

    VolatilePtr(const pointer _p) {
        ptr = _p;
        prev = this;
        next = this;
    }

    VolatilePtr(const Self_& _vp) {
        ptr = _vp.ptr;
        prev = this;
        next = this;
    }

    VolatilePtr(SelfRef_ _vp) {
        ptr = _vp.ptr;
        prev = this;
        next = this;
        if (ptr) hangOn(_vp);
    }

    ~VolatilePtr() {
        hangOff();
    }

    template <typename size_type>
    inline reference operator[] (size_type offset) {
        return ptr[offset];
    }

    template <typename size_type>
    inline const_reference operator[] (size_type offset) const {
        return ptr[offset];
    }

    inline Self_& operator=(Self_ const &Right_) {
        hangOff();
        ptr = Right_.ptr;
        if (ptr) hangOn(const_cast<Self_&>(Right_));
        return *this;
    }

    inline Self_& operator=(pointer const Right_) {
        hangOff();
        ptr = Right_;
        return *this;
    }

    // TODO(holtgrew): Move to global function?
    inline bool isLonely() {
        return next == this;
    }

    // TODO(holtgrew): Move to global function?
    inline void nukeCopies() {
        SelfPtr_ p = next;
        while (p != this) {
            SelfPtr_ tmp = p->next;
            p->ptr = NULL;
            p->prev = p;
            p->next = p;
            p = tmp;
        }
        prev = this;
        next = this;
    }

    // TODO(holtgrew): Move to global function?
    inline bool operator== (const Self_ &I) const {
        return ptr == I.ptr;
    }

    // TODO(holtgrew): Move to global function?
    inline bool operator!= (const Self_ &I) const {
        return ptr != I.ptr;
    }

    inline operator pointer () const {
        return ptr;
    }

  private:

    inline void hangOn(SelfRef_ _prev) {
        // hang on between _prev and _prev.next
        prev = &_prev;
        next = _prev.next;
        _prev.next = this;
        next->prev = this;
    }

    inline void hangOff() {
        next->prev = prev;
        prev->next = next;
        next = this;
        prev = this;
    }
};

// ============================================================================
// Metafunctions
// ============================================================================

// ============================================================================
// Functions
// ============================================================================

// ----------------------------------------------------------------------------
// Function nukeCopies()
// ----------------------------------------------------------------------------

/*!
 * @fn VolatilePtr#nukeCopies
 * @brief Reset all pointers connected to a given one.
 *
 * @signature void nukeCopies(ptr);
 *
 * @param[in] ptr One pointer of the connected component to reset.
 */

// TODO(holtgrew): Remove this version?
template <typename TValue>
inline void nukeCopies(TValue * &)
{
}

template <typename TValue>
inline void nukeCopies(VolatilePtr<TValue> & ptr)
{
    ptr.nukeCopies();
}

}  // namespace seqan

#endif  // #ifndef SEQAN_BASIC_BASIC_VOLATILE_PTR_H_
