/**
 * @file llbufferstream.cpp
 * @author Phoenix
 * @date 2005-10-10
 * @brief Implementation of the buffer iostream classes
 *
 * $LicenseInfo:firstyear=2005&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#include "linden_common.h"
#include "llbufferstream.h"

#include "llbuffer.h"
#include "llthread.h"
#include "llmutex.h"

static const S32 DEFAULT_OUTPUT_SEGMENT_SIZE = 1024 * 4;

/*
 * LLBufferStreamBuf
 */
LLBufferStreamBuf::LLBufferStreamBuf(
    const LLChannelDescriptors& channels,
    LLBufferArray* buffer) :
    mChannels(channels),
    mBuffer(buffer)
{
}

LLBufferStreamBuf::~LLBufferStreamBuf()
{
    sync();
}

// virtual
int LLBufferStreamBuf::underflow()
{
    //LL_DEBUGS() << "LLBufferStreamBuf::underflow()" << LL_ENDL;
    if(!mBuffer)
    {
        return EOF;
    }

    LLMutexLock lock(mBuffer->getMutex());
    LLBufferArray::segment_iterator_t iter;
    LLBufferArray::segment_iterator_t end = mBuffer->endSegment();
    U8* last_pos = (U8*)gptr();
    LLSegment segment;
    if(last_pos)
    {
        // Back up into a piece of memory we know that we have
        // allocated so that calls for the next segment based on
        // 'after' will succeed.
        --last_pos;
        iter = mBuffer->splitAfter(last_pos);
        if(iter != end)
        {
            // We need to clear the read segment just in case we have
            // an early exit in the function and never collect the
            // next segment. Calling eraseSegment() with the same
            // segment twice is just like double deleting -- nothing
            // good comes from it.
            mBuffer->eraseSegment(iter++);
            if(iter != end) segment = (*iter);
        }
        else
        {
            // This should never really happen, but somehow, the
            // istream is telling the buf that it just finished
            // reading memory that is not in the buf. I think this
            // would only happen if there were a bug in the c++ stream
            // class. Just bail.
            // *TODO: can we set the fail bit on the stream somehow?
            return EOF;
        }
    }
    else
    {
        // Get iterator to full segment containing last_pos
        // and construct sub-segment starting at last_pos.
        // Note: segment may != *it at this point
        iter = mBuffer->constructSegmentAfter(last_pos, segment);
    }
    if(iter == end)
    {
        return EOF;
    }

    // Iterate through segments to find a non-empty segment on input channel.
    while((!segment.isOnChannel(mChannels.in()) || (segment.size() == 0)))
    {
        ++iter;
        if(iter == end)
        {
            return EOF;
        }

        segment = *(iter);
    }

    // set up the stream to read from the next segment.
    char* start = (char*)segment.data();
    setg(start, start, start + segment.size());
    return *gptr();
}

// virtual
int LLBufferStreamBuf::overflow(int c)
{
    if(!mBuffer)
    {
        return EOF;
    }
    if(EOF == c)
    {
        // if someone puts an EOF, I suppose we should sync and return
        // success.
        if(0 == sync())
        {
            return 1;
        }
        else
        {
            return EOF;
        }
    }

    // since we got here, we have a buffer, and we have a character to
    // put on it.
    LLBufferArray::segment_iterator_t it;
    LLMutexLock lock(mBuffer->getMutex());
    it = mBuffer->makeSegment(mChannels.out(), DEFAULT_OUTPUT_SEGMENT_SIZE);
    if(it != mBuffer->endSegment())
    {
        char* start = (char*)(*it).data();
        (*start) = (char)(c);
        setp(start + 1, start + (*it).size());
        return c;
    }
    else
    {
        return EOF;
    }
}

// virtual
int LLBufferStreamBuf::sync()
{
    int return_value = -1;
    if(!mBuffer)
    {
        return return_value;
    }

    // This chunk of code is not necessary because typically, users of
    // the stream will read until EOF. Therefore, underflow was called
    // and the segment was discarded before the sync() was called in
    // the destructor. Theoretically, we could keep some more data
    // around and detect the rare case where an istream was deleted
    // before reading to the end, but that will only leave behind some
    // unavailable but still referenced memory. Also, if another
    // istream is constructed, it will re-read that segment, and then
    // discard it.
    //U8* last_pos = (U8*)gptr();
    //if(last_pos)
    //{
    //  // Looks like we read something. Discard what we have read.
    //  // gptr() actually returns the currrent position, but we call
    //  // it last_pos because of how it is used in the split call
    //  // below.
    //  --last_pos;
    //  LLBufferArray::segment_iterator_t iter;
    //  iter = mBuffer->splitAfter(last_pos);
    //  if(iter != mBuffer->endSegment())
    //  {
    //      // We need to clear the read segment just in case we have
    //      // an early exit in the function and never collect the
    //      // next segment. Calling eraseSegment() with the same
    //      // segment twice is just like double deleting -- nothing
    //      // good comes from it.
    //      mBuffer->eraseSegment(iter);
    //  }
    //}

    // set the put pointer so that we force an overflow on the next
    // write.
    U8* address = (U8*)pptr();
    setp(NULL, NULL);

    // *NOTE: I bet we could just --address if address is not NULL.
    // Need to think about that.
    LLMutexLock lock(mBuffer->getMutex());
    address = mBuffer->seek(mChannels.out(), address, -1);
    if(address)
    {
        LLBufferArray::segment_iterator_t it;
        it = mBuffer->splitAfter(address);
        LLBufferArray::segment_iterator_t end = mBuffer->endSegment();
        if(it != end)
        {
            ++it;
            if(it != end)
            {
                mBuffer->eraseSegment(it);
            }
            return_value = 0;
        }
    }
    else
    {
        // nothing was put on the buffer, so the sync() is a no-op.
        return_value = 0;
    }
    return return_value;
}

// virtual
#if( LL_WINDOWS || __GNUC__ > 2)
LLBufferStreamBuf::pos_type LLBufferStreamBuf::seekoff(
    LLBufferStreamBuf::off_type off,
    std::ios::seekdir way,
    std::ios::openmode which)
#else
streampos LLBufferStreamBuf::seekoff(
    streamoff off,
    std::ios::seekdir way,
    std::ios::openmode which)
#endif
{
    if(!mBuffer
       || ((way == std::ios::beg) && (off < 0))
       || ((way == std::ios::end) && (off > 0)))
    {
        return -1;
    }
    U8* address = NULL;
    if(which & std::ios::in)
    {
        U8* base_addr = NULL;
        switch(way)
        {
        case std::ios::end:
            base_addr = (U8*)LLBufferArray::npos;
            break;
        case std::ios::cur:
            // get the current get pointer and adjust it for buffer
            // array semantics.
            base_addr = (U8*)gptr();
            break;
        case std::ios::beg:
        default:
            // NULL is fine
            break;
        }

        LLMutexLock lock(mBuffer->getMutex());
        address = mBuffer->seek(mChannels.in(), base_addr, (S32)off);
        if(address)
        {
            LLBufferArray::segment_iterator_t iter;
            iter = mBuffer->getSegment(address);
            char* start = (char*)(*iter).data();
            setg(start, (char*)address, start + (*iter).size());
        }
        else
        {
            address = (U8*)(-1);
        }
    }
    if(which & std::ios::out)
    {
        U8* base_addr = NULL;
        switch(way)
        {
        case std::ios::end:
            base_addr = (U8*)LLBufferArray::npos;
            break;
        case std::ios::cur:
            // get the current put pointer and adjust it for buffer
            // array semantics.
            base_addr = (U8*)pptr();
            break;
        case std::ios::beg:
        default:
            // NULL is fine
            break;
        }

        LLMutexLock lock(mBuffer->getMutex());
        address = mBuffer->seek(mChannels.out(), base_addr, (S32)off);
        if(address)
        {
            LLBufferArray::segment_iterator_t iter;
            iter = mBuffer->getSegment(address);
            setp((char*)address, (char*)(*iter).data() + (*iter).size());
        }
        else
        {
            address = (U8*)(-1);
        }
    }

#if( LL_WINDOWS || __GNUC__ > 2 )
    S32 rv = (S32)(intptr_t)address;
    return (pos_type)rv;
#else
    return (streampos)address;
#endif
}


/*
 * LLBufferStream
 */
LLBufferStream::LLBufferStream(
    const LLChannelDescriptors& channels,
    LLBufferArray* buffer) :
    std::iostream(&mStreamBuf),
    mStreamBuf(channels, buffer)
{
}

LLBufferStream::~LLBufferStream()
{
}