/*
 * Copyright (c) 2003-2008 by FlashCode <flashcode@flashtux.org>
 * See README for License detail, AUTHORS for developers list.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/* logger-tail.c: return last lines of a file */


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

#include "logger.h"
#include "logger-tail.h"


#define LOGGER_TAIL_BUFSIZE 4096


/*
 * logger_tail_last_eol: find last eol in a string
 */

char *
logger_tail_last_eol (const char *string_start, const char *string_ptr)
{
    while (string_ptr >= string_start)
    {
        if ((string_ptr[0] == '\n') || (string_ptr[0] == '\r'))
            return (char *)string_ptr;
        string_ptr--;
    }
    
    /* no end-of-line found in string */
    return NULL;
}

/*
 * logger_tail_file: return last lines of a file
 */

struct t_logger_line *
logger_tail_file (const char *filename, int n_lines)
{
    int fd;
    off_t file_length, file_pos;
    size_t to_read;
    ssize_t bytes_read;
    char buf[LOGGER_TAIL_BUFSIZE + 1];
    char *ptr_buf, *pos_eol, *part_of_line, *new_part_of_line;
    struct t_logger_line *ptr_line, *new_line;
    
    /* open file */
    fd = open (filename, O_RDONLY);
    if (fd == -1)
        return NULL;
    
    /* seek to the end of file */
    file_length = lseek (fd, (off_t)0, SEEK_END);
    if (file_length <= 0)
    {
        close (fd);
        return NULL;
    }
    to_read = file_length;
    file_pos = file_length - LOGGER_TAIL_BUFSIZE;
    if (file_pos < 0)
        file_pos = 0;
    else
        to_read = LOGGER_TAIL_BUFSIZE;
    lseek (fd, file_pos, SEEK_SET);
    
    /* loop until we have "n_lines" lines in list */
    part_of_line = NULL;
    ptr_line = NULL;
    while (n_lines > 0)
    {
        lseek (fd, file_pos, SEEK_SET);
        bytes_read = read (fd, buf, to_read);
        if (bytes_read <= 0)
        {
            logger_tail_free (ptr_line);
            close (fd);
            return NULL;
        }
        buf[bytes_read] = '\0';
        ptr_buf = buf + bytes_read - 1;
        while (ptr_buf && (ptr_buf >= buf))
        {
            pos_eol = logger_tail_last_eol (buf, ptr_buf);
            if ((pos_eol && pos_eol[1]) || (!pos_eol && (file_pos == 0)))
            {
                /* use data and part_of_line (if existing) to build a new line */
                if (!pos_eol)
                {
                    ptr_buf = NULL;
                    pos_eol = buf;
                }
                else
                {
                    ptr_buf = pos_eol - 1;
                    pos_eol[0] = '\0';
                    pos_eol++;
                }
                new_line = malloc (sizeof (*new_line));
                if (!new_line)
                {
                    logger_tail_free (ptr_line);
                    ptr_line = NULL;
                    break;
                }
                if (part_of_line)
                {
                    new_line->data = malloc ((strlen (pos_eol) +
                                              strlen (part_of_line) + 1));
                    if (!new_line->data)
                    {
                        free (part_of_line);
                        logger_tail_free (ptr_line);
                        close (fd);
                        return NULL;
                    }
                    strcpy (new_line->data, pos_eol);
                    strcat (new_line->data, part_of_line);
                    free (part_of_line);
                    part_of_line = NULL;
                }
                else
                {
                    new_line->data = strdup (pos_eol);
                }
                new_line->next_line = ptr_line;
                ptr_line = new_line;
                n_lines--;
                if (n_lines <= 0)
                    break;
            }
            else if (!pos_eol)
            {
                /* beginning of read buffer reached without EOL, then we
                   add string to part_of_line, we'll use that later */
                if (part_of_line)
                {
                    new_part_of_line = malloc (strlen (buf) + strlen (part_of_line) + 1);
                    if (!new_part_of_line)
                    {
                        free (part_of_line);
                        logger_tail_free (ptr_line);
                        close (fd);
                        return NULL;
                    }
                    strcpy (new_part_of_line, buf);
                    strcat (new_part_of_line, part_of_line);
                    free (part_of_line);
                    part_of_line = new_part_of_line;
                }
                else
                {
                    part_of_line = malloc (strlen (buf) + 1);
                    strcpy (part_of_line, buf);
                }
                ptr_buf = NULL;
            }
            else
                ptr_buf = pos_eol - 1;
        }
        if (file_pos == 0)
            break;
        to_read = file_pos;
        file_pos -= LOGGER_TAIL_BUFSIZE;
        if (file_pos < 0)
            file_pos = 0;
        else
            to_read = LOGGER_TAIL_BUFSIZE;
    }
    
    if (part_of_line)
        free (part_of_line);
    
    close (fd);
    
    return ptr_line;
}

/*
 * logger_tail_free: free structure returned by "logger_tail_file" function
 */

void
logger_tail_free (struct t_logger_line *lines)
{
    if (!lines)
        return;
    
    while (lines->next_line)
    {
        if (lines->data)
            free (lines->data);
        lines = lines->next_line;
    }
    free (lines);
}