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

char * read_first_line(const char * filename) {
    int fd;
    char *endptr;
    char *cipherstring;

    // open file
    fd = open(filename, O_RDONLY, (mode_t)0600);
    if (fd == -1) {
        perror("Error opening file");
        exit(EXIT_FAILURE);
    }
    // get length
    struct stat fileInfo = {0};
    if (fstat(fd, &fileInfo) == -1) {
        perror("Error getting the file size");
        exit(EXIT_FAILURE);
    }
    if (fileInfo.st_size == 0) {
        fprintf(stderr, "Error: File is empty, nothing to do\n");
        exit(EXIT_FAILURE);
    }
    // mmap file
    char *map = mmap(0, fileInfo.st_size, PROT_READ, MAP_SHARED, fd, 0);
    if (map == MAP_FAILED)
    {
        close(fd);
        perror("Error mmapping the file");
        exit(EXIT_FAILURE);
    }
    // find first line
    endptr = strchrnul(map, 0x0a);

    size_t cipherstring_len = endptr - map;
    cipherstring = malloc(cipherstring_len+1);
    strncpy(cipherstring, map, cipherstring_len);

    // munmap and close file
    if (munmap(map, fileInfo.st_size) == -1)
    {
        close(fd);
        perror("Error un-mmapping the file");
        exit(EXIT_FAILURE);
    }
    close(fd);

    return cipherstring;
}