//
// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE.md file in the project root for full license information.
//

#define _CRT_SECURE_NO_WARNINGS
#include "BufferedFileReader.h"

namespace CNTK {

    using namespace std;

    BufferedFileReader::BufferedFileReader(size_t maxSize, const FileWrapper& file) 
        : m_maxSize(maxSize), m_file(file)
    {
        m_file.CheckIsOpenOrDie();

        if (maxSize == 0)
            RuntimeError("Max buffer size cannot be zero.");

        m_buffer.reserve(maxSize);

        Refill();
    }

    void BufferedFileReader::Refill()
    {
        if (m_done)
            return;

        m_index = 0;
        m_fileOffset = m_file.TellOrDie();

        m_buffer.resize(m_maxSize);
        size_t bytesRead = m_file.Read(m_buffer.data(), 1, m_maxSize);

        if (bytesRead != m_maxSize && !m_file.ReachedEOF())
            RuntimeError("Error reading file '%ls': %s.", m_file.Filename().c_str(), strerror(errno));
        
        m_buffer.resize(bytesRead);
        m_done = (bytesRead == 0);
    }

    bool BufferedFileReader::TryMoveToNextLine()
    {
        for (; !m_done; Refill())
        {
            auto start = m_buffer.data() + m_index;
            auto found = (char*)memchr(start, g_eol, m_buffer.size() - m_index);
            if (found)
            {
                m_index = (found - m_buffer.data());
                // At this point, m_index points to the end of line, try moving it to the next line.
                return Pop();
            }
        }

        return false;
    }

    // Reads the current line (i.e., everything that's left on the current line) into the provided 
    // string reference (omitting the trailing EOL). Returns false upon reaching the EOF.
    bool BufferedFileReader::TryReadLine(string& str)
    {
        if (m_done)
            return false;

        str.resize(0);
        bool result = false;
        for (; !m_done; Refill())
        {
            auto start = m_buffer.data() + m_index;
            auto found = (char*)memchr(start, g_eol, m_buffer.size() - m_index);
            if (found)
            {
                m_index = (found - m_buffer.data());
                str.append(start, found - start);
                // At this point, m_index points to the end of line, try moving it to the next line.
                Pop();
                return true;
            }
            
            if (m_index < m_buffer.size())
            {
                // The current buffer doe not contain an end of line (for instance, when the line is so huge,
                // it does not fit in a single buffer). Append the remainder of the buffer to the string and refill.
                str.append(start, m_buffer.size() - m_index);
                result = true;
            }
        }

        return result;
    }
}