/*

 * Copyright 2013-2022 Step Function I/O, LLC

 *

 * Licensed to Green Energy Corp (www.greenenergycorp.com) and Step Function I/O

 * LLC (https://stepfunc.io) under one or more contributor license agreements.

 * See the NOTICE file distributed with this work for additional information

 * regarding copyright ownership. Green Energy Corp and Step Function I/O LLC license

 * 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 OPENDNP3_SHIFTABLEBUFFER_H

#define OPENDNP3_SHIFTABLEBUFFER_H

#include <ser4cpp/container/SequenceTypes.h>

namespace opendnp3

{

/** @section DESCRIPTION

        Implements a buffer that can shift its contents as it is read */

class ShiftableBuffer

{

public:

    /**

     * Construct the facade over the specified underlying buffer

     */

    ShiftableBuffer(uint8_t* pBuffer_, size_t size);

    // ------- Functions related to reading -----------

    size_t NumBytesRead() const

    {

        return writePos - readPos;

    }

    /// @return Pointer to the next byte to be read in the buffer

    ser4cpp::rseq_t ReadBuffer() const

    {

        return ser4cpp::rseq_t(pBuffer + readPos, NumBytesRead());

    }

    /// Signal that some bytes don't have to be stored any longer. They'll be recovered during the next shift operation.

    void AdvanceRead(size_t aNumBytes);

    // ------- Functions related to writing -----------

    /// Shift the buffer back to front, writing over bytes that have already been read. The objective

    /// being to free space for further writing.

    void Shift();

    /// Reset the buffer to its initial state, empty

    void Reset();

    /// @return Bytes of available for writing

    size_t NumWriteBytes() const

    {

        return M_SIZE - writePos;

    }

    /// @return Pointer to the position in the buffer available for writing

    uint8_t* WriteBuff() const

    {

        return pBuffer + writePos;

    }

    /// Signal to the buffer bytes were written to the current write position

    void AdvanceWrite(size_t numBytes);

    ////////////////////////////////////////////

    // Other functions

    ////////////////////////////////////////////

    /// Searches the read subsequence for 0x0564 sync bytes

    /// @return true if both sync bytes were found in the buffer.

    bool Sync(size_t& skipCount);

private:

    uint8_t* pBuffer;

    const size_t M_SIZE;

    size_t writePos;

    size_t readPos;

};

} // namespace opendnp3

#endif