/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
#ifndef StackBounds_h
#define StackBounds_h

#include <algorithm>

namespace WTF {

class StackBounds {
    // This 64k number was picked because a sampling of stack usage differences
    // between consecutive entries into one of the Interpreter::execute...()
    // functions was seen to be as high as 27k. Hence, 64k is chosen as a
    // conservative availability value that is not too large but comfortably
    // exceeds 27k with some buffer for error.
    const static size_t s_defaultAvailabilityDelta = 64 * 1024;

public:
    static StackBounds emptyBounds() { return StackBounds(); }

    static StackBounds currentThreadStackBounds()
    {
        StackBounds bounds;
        bounds.initialize();
        bounds.checkConsistency();
        return bounds;
    }

    StackBounds(void* origin, void* end)
        : m_origin(origin)
        , m_bound(end)
    {
        checkConsistency();
    }

    void* origin() const
    {
        ASSERT(m_origin);
        return m_origin;
    }

    void* end() const
    {
        ASSERT(m_bound);
        return m_bound;
    }
    
    size_t size() const
    {
        if (isGrowingDownward())
            return static_cast<char*>(m_origin) - static_cast<char*>(m_bound);
        return static_cast<char*>(m_bound) - static_cast<char*>(m_origin);
    }

    bool isEmpty() const { return !m_origin; }

    bool contains(void* p) const
    {
        if (isEmpty())
            return false;
        if (isGrowingDownward())
            return (m_origin >= p) && (p > m_bound);
        return (m_bound > p) && (p >= m_origin);
    }

    void* recursionLimit(size_t minAvailableDelta = s_defaultAvailabilityDelta) const
    {
        checkConsistency();
        if (isGrowingDownward())
            return static_cast<char*>(m_bound) + minAvailableDelta;
        return static_cast<char*>(m_bound) - minAvailableDelta;
    }

    void* recursionLimit(char* startOfUserStack, size_t maxUserStack, size_t reservedZoneSize) const
    {
        checkConsistency();
        if (maxUserStack < reservedZoneSize)
            reservedZoneSize = maxUserStack;
        size_t maxUserStackWithReservedZone = maxUserStack - reservedZoneSize;

        if (isGrowingDownward()) {
            char* endOfStackWithReservedZone = reinterpret_cast<char*>(m_bound) + reservedZoneSize;
            if (startOfUserStack < endOfStackWithReservedZone)
                return endOfStackWithReservedZone;
            size_t availableUserStack = startOfUserStack - endOfStackWithReservedZone;
            if (maxUserStackWithReservedZone > availableUserStack)
                maxUserStackWithReservedZone = availableUserStack;
            return startOfUserStack - maxUserStackWithReservedZone;
        }

        char* endOfStackWithReservedZone = reinterpret_cast<char*>(m_bound) - reservedZoneSize;
        if (startOfUserStack > endOfStackWithReservedZone)
            return endOfStackWithReservedZone;
        size_t availableUserStack = endOfStackWithReservedZone - startOfUserStack;
        if (maxUserStackWithReservedZone > availableUserStack)
            maxUserStackWithReservedZone = availableUserStack;
        return startOfUserStack + maxUserStackWithReservedZone;
    }

    bool isGrowingDownward() const
    {
        ASSERT(m_origin && m_bound);
        return true;
    }

private:
    StackBounds()
        : m_origin(0)
        , m_bound(0)
    {
    }

    WTF_EXPORT_PRIVATE void initialize();

    void checkConsistency() const
    {
#if !ASSERT_DISABLED
        void* currentPosition = &currentPosition;
        ASSERT(m_origin != m_bound);
        ASSERT(isGrowingDownward()
            ? (currentPosition < m_origin && currentPosition > m_bound)
            : (currentPosition > m_origin && currentPosition < m_bound));
#endif
    }

    void* m_origin;
    void* m_bound;

    friend class StackStats;
};

} // namespace WTF

using WTF::StackBounds;

#endif