/*

 *    Copyright (c) 2021 Project CHIP Authors

 *

 *    Licensed 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.

 */

/**

 *    @file

 *      This file defines the CHIP message counters.

 *

 */

#pragma once

#include <crypto/RandUtils.h>

#include <lib/core/CHIPError.h>

#include <stdint.h>

namespace chip {

/**

 * MessageCounter represents a local message counter. There are 2 types of message counter

 *

 * 1. Global unencrypted message counter

 * 2. Secure session message counter

 *

 * There will be separate implementations for each type

 */

class MessageCounter

{

public:

    static constexpr uint32_t kMessageCounterRandomInitMask = 0x0FFFFFFF; ///< 28-bit mask

    enum Type : uint8_t

    {

        GlobalUnencrypted,

        GlobalEncrypted,

        Session,

    };

    virtual ~MessageCounter() = default;

    virtual Type GetType() const                           = 0;

    virtual CHIP_ERROR AdvanceAndConsume(uint32_t & fetch) = 0; /** Advance the counter, and feed the new counter to fetch */

    // Note: this function must be called after Crypto is initialized. It can not be called from global variable constructor.

    static uint32_t GetDefaultInitialValuePredecessor() { return Crypto::GetRandU32() & kMessageCounterRandomInitMask; }

};

class GlobalUnencryptedMessageCounter : public MessageCounter

{

public:

    GlobalUnencryptedMessageCounter() : mLastUsedValue(0) {}

    void Init() { mLastUsedValue = GetDefaultInitialValuePredecessor(); }

    Type GetType() const override { return GlobalUnencrypted; }

    CHIP_ERROR AdvanceAndConsume(uint32_t & fetch) override

    {

        fetch = ++mLastUsedValue;

        return CHIP_NO_ERROR;

    }

private:

    uint32_t mLastUsedValue;

};

class LocalSessionMessageCounter : public MessageCounter

{

public:

    static constexpr uint32_t kMessageCounterMax = 0xFFFFFFFF;

    /**

     * Initialize a local message counter with random value between [1, 2^28]. This increases the difficulty of traffic analysis

     * attacks by making it harder to determine how long a particular session has been open. The initial counter is always 1 or

     * higher to guarantee first message is always greater than initial peer counter set to 0.

     *

     * The mLastUsedValue is the predecessor of the initial value, it will be advanced before using, so don't need to add 1 here.

     */

    LocalSessionMessageCounter() { mLastUsedValue = GetDefaultInitialValuePredecessor(); }

    Type GetType() const override { return Session; }

    CHIP_ERROR AdvanceAndConsume(uint32_t & fetch) override

    {

        if (mLastUsedValue == kMessageCounterMax)

        {

            return CHIP_ERROR_MESSAGE_COUNTER_EXHAUSTED;

        }

        fetch = ++mLastUsedValue;

        return CHIP_NO_ERROR;

    }

    // Test-only function to set the counter value

    void TestSetCounter(uint32_t value) { mLastUsedValue = value; }

private:

    uint32_t mLastUsedValue;

};

} // namespace chip