/*

    Task Spooler - a task queue system for the unix user

    Copyright (C) 2007-2008  Lluís Batlle i Rossell

    Please find the license in the provided COPYING file.

*/

#include <unistd.h>

#include <fcntl.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <stdio.h>

#include <errno.h>

#include <string.h>

#include <stdlib.h>

#include <sys/time.h> /* Dep de main.h */

#include "main.h"

enum { BSIZE=1024 };

static int min(int a, int b)

{

    if (a < b)

        return a;

    return b;

}

static int max(int a, int b)

{

    if (a > b)

        return a;

    return b;

}

static void tail_error(const char *str)

{

    fprintf(stderr, "%s", str);

    fprintf(stderr, ". errno: %i (%s)\n",

                    errno, strerror(errno));

    exit(-1);

}

static void seek_at_last_lines(int fd, int lines)

{

    char buf[BSIZE];

    int lines_found = 0;

    int last_lseek = BSIZE;

    int last_read = 0; /* Only to catch not doing any loop */

    int move_offset;

    int i = -1; /* Only to catch not doing any loop */

    last_lseek = lseek(fd, 0, SEEK_END);

    do

    {

        int next_read;

        next_read = min(last_lseek, BSIZE);

        /* we should end looping if last_lseek == 0

         * This means we already read all the file. */

        if (next_read <= 0)

            break;

        /* last_lseek will be -1 at the beginning of the file,

         * if we wanted to go farer than it. */

        last_lseek = lseek(fd, -next_read, SEEK_CUR);

        if (last_lseek == -1)

            last_lseek = lseek(fd, 0, SEEK_SET);

        last_read = read(fd, buf, next_read);

        if (last_read == -1)

        {

            if (errno == EINTR)

                continue;

            tail_error("Error reading");

        }

        for(i = last_read-1; i >= 0; --i)

        {

            if (buf[i] == '\n')

            {

                ++lines_found;

                if (lines_found > lines)

                    /* We will use 'i' to calculate where to

                     * put the file cursor, before return. */

                    break;

            }

        }

        /* Go back the read bytes */

        last_lseek = lseek(fd, -last_read, SEEK_CUR);

    } while(lines_found < lines);

    /* Calculate the position */

    move_offset = i+1;

    lseek(fd, move_offset, SEEK_CUR);

}

static void set_non_blocking(int fd)

{

    long arg;

    arg = O_RDONLY | O_NONBLOCK;

    fcntl(fd, F_SETFL, arg);

}

/* if last_lines == -1, go on from the start of the file */

int tail_file(const char *fname, int last_lines)

{

    int fd;

    int res;

    int waiting_end = 1;

    int end_res = 0;

    int endfile_reached = 0;

    fd_set readset;

    fd = open(fname, O_RDONLY);

    if (fd == -1)

        tail_error("Error: Cannot open the outut file");

    if (last_lines >= 0)

        seek_at_last_lines(fd, last_lines);

    /* we don't want the next read calls to block. */

    set_non_blocking(fd);

    do

    {

        char buf[BSIZE];

        int maxfd;

        FD_ZERO(&readset);

        maxfd = -1;

        if (!endfile_reached)

        {

            FD_SET(fd, &readset);

            maxfd = fd;

        }

        if (waiting_end)

        {

            FD_SET(server_socket, &readset);

            maxfd = max(fd, server_socket);

        }

        /* If we don't have fd's to wait for, let's sleep */

        if (maxfd == -1)

        {

            usleep(1 /* sec */* 1000000);

        } else

        {

            /* Otherwise, do a normal select */

            struct timeval tv = {1 /*sec*/, 0 };

            res = select(maxfd + 1, &readset, 0, 0, &tv);

        }

        if (FD_ISSET(server_socket, &readset))

        {

            end_res = c_wait_job_recv();

            waiting_end = 0;

        }

        /* We always read when select awakes */

        res = read(fd, buf, BSIZE);

        if (res == -1)

        {

            if (errno == EINTR || errno == EAGAIN)

            {

                res = 1; /* Hack for the while condition */

                continue;

            }

            tail_error("Error reading");

        }

        if (res == 0)

            endfile_reached = 1;

        else

            endfile_reached = 0;

        write(1, buf, res);

    } while(!endfile_reached || waiting_end);

    close(fd);

    return end_res;

}