#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include "get_next_line.h"

#define GETNEXTLINE_BUF_LENGTH 3

char* flushBuffer(char* buffer, size_t* bufferSize, char readBuffer[GETNEXTLINE_BUF_LENGTH], size_t readBufLength)
{
    char* result;

    if (*bufferSize == 0 && readBufLength == 0)
        return NULL;
    result = (char*) malloc(sizeof(*buffer) * (*bufferSize + readBufLength +1));
    if (*bufferSize)
        memcpy(result, buffer, *bufferSize);
    memcpy(&result[*bufferSize], readBuffer, readBufLength);
    result[readBufLength + *bufferSize] = '\0';
    if (result[readBufLength + *bufferSize -1] == '\n')
        result[readBufLength + *bufferSize -1] = '\0';
    if (buffer)
        free(buffer);
    *bufferSize = *bufferSize + readBufLength;
    return result;
}

char* get_next_line(int fd)
{
    char* result;
    size_t resultSize;
    char buf[GETNEXTLINE_BUF_LENGTH];
    size_t bufPos;
    int rdResult;

    result = NULL;
    resultSize = 0;
    bufPos = 0;
    while (1)
    {
        rdResult = read(fd, &buf[bufPos], 1);
        if (rdResult < 0)
        {
            if (result != NULL)
                free(result);
            return NULL;
        }
        bufPos += rdResult;
        if (rdResult == 0 || buf[bufPos-rdResult] == '\n')
            break;
        if (bufPos == GETNEXTLINE_BUF_LENGTH)
        {
            result = flushBuffer(result, &resultSize, buf, bufPos);
            bufPos = 0;
        }
    }
    return flushBuffer(result, &resultSize, buf, bufPos);
}