#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

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

enum
{
    LINE_NUM = 2,
    DEC_BASE = 10,
    EXIT_STATUS_SUCCESS = 0,
    EXIT_STATUS_ERROR = 1
};

enum Args
{
    ARG_SELF,
    ARG_PATH,
    ARG_LINES,
    ARG_NUM = ARG_LINES + LINE_NUM
};

void
put_line(const unsigned char *file, ssize_t file_size, ssize_t off)
{
    while(off < file_size && file[off] != '\n') {
        putchar_unlocked(file[off++]);
    }
    putchar_unlocked('\n');
}

int
main(int argc, char *argv[])
{
    int exit_status = EXIT_STATUS_SUCCESS;
    errno = 0;
    if (argc < ARG_NUM) {
        fprintf(stderr, "error: Too few arguments. Expected %d, have %d\n", ARG_NUM - 1, argc - 1);
        exit_status = EXIT_STATUS_ERROR;
        goto exit0;
    }

    int fd;
    if ((fd = open(argv[ARG_PATH], O_RDONLY)) == -1) {
        perror("open");
        exit_status = EXIT_STATUS_ERROR;
        goto exit0;
    }

    long line[LINE_NUM];
    for (int i = 0; i < LINE_NUM; ++i)
    {
        char *temp;
        line[i] = strtol(argv[ARG_LINES + i], &temp, DEC_BASE);

        if (*temp) {
            fprintf(stderr, "strtol: Invalid value of argument %d\n", ARG_LINES + i - 1);
            exit_status = EXIT_STATUS_ERROR;
            goto exit1;
        } else if (errno) {
            perror("strtol");
            exit_status = EXIT_STATUS_ERROR;
            goto exit1;
        }
    }

    if (line[0] <= 0 || line[1] <= 0) {
        fprintf(stderr, "error: Non-positive argument\n");
        exit_status = EXIT_STATUS_ERROR;
        goto exit1;
    }

    if (line[0] >= line[1]) {
        goto exit1;
    }

    struct stat stat_buf;
    if (fstat(fd, &stat_buf)) {
        perror("fstat");
        exit_status = EXIT_STATUS_ERROR;
        goto exit1;
    }
    ssize_t filesize = 0;
    if (__builtin_add_overflow(0, stat_buf.st_size, &filesize)) {
        fprintf(stderr, "error: file too big\n");
        exit_status = EXIT_STATUS_ERROR;
        goto exit1;
    }

    if (!filesize) {
        goto exit1;
    }

    unsigned char *file = mmap(NULL, filesize, PROT_READ, MAP_PRIVATE, fd, 0);
    if (errno) {
        perror("mmap");
        exit_status = EXIT_STATUS_ERROR;
        goto exit1;
    }

    ssize_t off = 0, start = -1, end = -1;

    while (off < filesize) {
        if (line[0] == 1) {
            start = off;
        }
        if (line[1] == 1) {
            end = off - 1;
            break;
        }

        while(off < filesize && file[off] != '\n') {
            ++off;
        }
        if (off < filesize) {
            ++off;
        }

        --line[0];
        --line[1];
    }

    if (start == -1) {
        goto exit2;
    }

    if (end == -1) {
        end = filesize - 1;
    }

    while (end >= start) {
        while (end > start && file[end - 1] != '\n') {
            --end;
        }
        put_line(file, filesize, end--);
    }

exit2:
    munmap(file, filesize);

exit1:
    close(fd);

exit0:
    return exit_status;
}