/****************************************************************************
**
** Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
** Contact: http://www.qt.io/licensing/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
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****************************************************************************/
#ifndef QDUPLICATETRACKER_P_H
#define QDUPLICATETRACKER_P_H

//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//

#include <qglobal.h>

#if defined(__cpp_lib_memory_resource) && __cplusplus > 201402L
#  include <unordered_set>
#  include <memory_resource>
#else
#  include <qset.h>
#endif

QT_BEGIN_NAMESPACE

template <typename T, size_t Prealloc = 32>
class QDuplicateTracker {
#ifdef __cpp_lib_memory_resource
    struct node_guesstimate { void *next; size_t hash; T value; };
    static constexpr size_t bufferSize(size_t N) {
        return N * sizeof(void*) // bucket list
                + N * sizeof(node_guesstimate); // nodes
    }

    char buffer[bufferSize(Prealloc)];
    std::pmr::monotonic_buffer_resource res{buffer, sizeof buffer};
    std::pmr::unordered_set<T> set{Prealloc, &res};
#else
    static QSet<T> makeQSet() { QSet<T> r; r.reserve(Prealloc); return r; }
    QSet<T> set = makeQSet();
    int setSize = 0;
#endif
    Q_DISABLE_COPY_MOVE(QDuplicateTracker);
public:
    QDuplicateTracker() = default;
    void reserve(int n) { set.reserve(n); }
    Q_REQUIRED_RESULT bool hasSeen(const T &s)
    {
        bool inserted;
#ifdef __cpp_lib_memory_resource
        inserted = set.insert(s).second;
#else
        set.insert(s);
        const int n = set.size();
        inserted = qExchange(setSize, n) != n;
#endif
        return !inserted;
    }
};

QT_END_NAMESPACE

#endif /* QDUPLICATETRACKER_P_H */