/*
 * Copyright (C) 2023 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include "Structure.h"

namespace JSC {

DECLARE_ALLOCATOR_WITH_HEAP_IDENTIFIER(MegamorphicCache);

class MegamorphicCache {
    WTF_MAKE_FAST_ALLOCATED;
    WTF_MAKE_NONCOPYABLE(MegamorphicCache);
public:
    static constexpr uint32_t primarySize = 2048;
    static constexpr uint32_t secondarySize = 512;
    static_assert(hasOneBitSet(primarySize), "size should be a power of two.");
    static_assert(hasOneBitSet(secondarySize), "size should be a power of two.");
    static constexpr uint32_t primaryMask = primarySize - 1;
    static constexpr uint32_t secondaryMask = secondarySize - 1;

    static constexpr uint16_t invalidEpoch = 0;
    static constexpr PropertyOffset maxOffset = UINT16_MAX;

    struct Entry {
        static ptrdiff_t offsetOfUid() { return OBJECT_OFFSETOF(Entry, m_uid); }
        static ptrdiff_t offsetOfStructureID() { return OBJECT_OFFSETOF(Entry, m_structureID); }
        static ptrdiff_t offsetOfEpoch() { return OBJECT_OFFSETOF(Entry, m_epoch); }
        static ptrdiff_t offsetOfOffset() { return OBJECT_OFFSETOF(Entry, m_offset); }
        static ptrdiff_t offsetOfHolder() { return OBJECT_OFFSETOF(Entry, m_holder); }

        void initAsMiss(StructureID structureID, UniquedStringImpl* uid, uint16_t epoch)
        {
            m_uid = uid;
            m_structureID = structureID;
            m_epoch = epoch;
            m_offset = 0;
            m_holder = nullptr;
        }

        void initAsHit(StructureID structureID, UniquedStringImpl* uid, uint16_t epoch, JSCell* holder, uint16_t offset, bool ownProperty)
        {
            m_uid = uid;
            m_structureID = structureID;
            m_epoch = epoch;
            m_offset = offset;
            m_holder = (ownProperty) ? JSCell::seenMultipleCalleeObjects() : holder;
        }

        RefPtr<UniquedStringImpl> m_uid;
        StructureID m_structureID { };
        uint16_t m_epoch { invalidEpoch };
        uint16_t m_offset { 0 };
        JSCell* m_holder { nullptr };
    };

    static ptrdiff_t offsetOfPrimaryEntries() { return OBJECT_OFFSETOF(MegamorphicCache, m_primaryEntries); }
    static ptrdiff_t offsetOfSecondaryEntries() { return OBJECT_OFFSETOF(MegamorphicCache, m_secondaryEntries); }
    static ptrdiff_t offsetOfEpoch() { return OBJECT_OFFSETOF(MegamorphicCache, m_epoch); }

    MegamorphicCache() = default;

#if CPU(ADDRESS64) && !ENABLE(STRUCTURE_ID_WITH_SHIFT)
    // Because Structure is allocated with 16-byte alignment, we should assume that StructureID's lower 4 bits are zeros.
    static constexpr unsigned structureIDHashShift1 = 4;
#else
    // When using STRUCTURE_ID_WITH_SHIFT, all bits can be different. Thus we do not need to shift the first level.
    static constexpr unsigned structureIDHashShift1 = 0;
#endif
    static constexpr unsigned structureIDHashShift2 = structureIDHashShift1 + 11;

    static constexpr unsigned structureIDHashShift3 = structureIDHashShift1 + 9;

    ALWAYS_INLINE static uint32_t primaryHash(StructureID structureID, UniquedStringImpl* uid)
    {
        uint32_t sid = bitwise_cast<uint32_t>(structureID);
        return ((sid >> structureIDHashShift1) ^ (sid >> structureIDHashShift2)) + uid->hash();
    }

    ALWAYS_INLINE static uint32_t secondaryHash(StructureID structureID, UniquedStringImpl* uid)
    {
        uint32_t key = bitwise_cast<uint32_t>(structureID) + static_cast<uint32_t>(bitwise_cast<uintptr_t>(uid));
        return key + (key >> structureIDHashShift3);
    }

    JS_EXPORT_PRIVATE void age(CollectionScope);

    void initAsMiss(StructureID structureID, UniquedStringImpl* uid)
    {
        uint32_t primaryIndex = MegamorphicCache::primaryHash(structureID, uid) & primaryMask;
        auto& entry = m_primaryEntries[primaryIndex];
        if (entry.m_epoch == m_epoch) {
            uint32_t secondaryIndex = MegamorphicCache::secondaryHash(entry.m_structureID, entry.m_uid.get()) & secondaryMask;
            m_secondaryEntries[secondaryIndex] = WTFMove(entry);
        }
        m_primaryEntries[primaryIndex].initAsMiss(structureID, uid, m_epoch);
    }

    void initAsHit(StructureID structureID, UniquedStringImpl* uid, JSCell* holder, uint16_t offset, bool ownProperty)
    {
        uint32_t primaryIndex = MegamorphicCache::primaryHash(structureID, uid) & primaryMask;
        auto& entry = m_primaryEntries[primaryIndex];
        if (entry.m_epoch == m_epoch) {
            uint32_t secondaryIndex = MegamorphicCache::secondaryHash(entry.m_structureID, entry.m_uid.get()) & secondaryMask;
            m_secondaryEntries[secondaryIndex] = WTFMove(entry);
        }
        m_primaryEntries[primaryIndex].initAsHit(structureID, uid, m_epoch, holder, offset, ownProperty);
    }

    uint16_t epoch() const { return m_epoch; }

    void bumpEpoch()
    {
        ++m_epoch;
        if (UNLIKELY(m_epoch == invalidEpoch))
            clearEntries();
    }

private:
    JS_EXPORT_PRIVATE void clearEntries();

    std::array<Entry, primarySize> m_primaryEntries { };
    std::array<Entry, secondarySize> m_secondaryEntries { };
    uint16_t m_epoch { 1 };
};

} // namespace JSC
