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


const char *usr_help_str = "Usage : ./mmap [-file filename]";

int main(int argc, char *argv[]){

    struct stat sb;

    char *filename = 0;
    for (int i = 1; argv[i]; ++i) {
        if (strcmp(argv[i], "-file") == 0){
            filename = argv[i+1]; i++;
        }
    }

    if (filename == 0){
        puts(usr_help_str);
        exit(1);
    }

    int fd = -1;
    if ((fd=open(filename,O_RDONLY,0666))==0){
        fprintf(stderr,"can't open %s\n",filename);
    }

    if (fstat(fd,&sb)){
        fprintf(stderr,"can't open %s\n",filename);
    }

    int file_size = sb.st_size;
    int page_size = getpagesize();

    int loop_num = file_size / page_size;
    loop_num += (file_size % page_size != 0);

    char * file_mmap = NULL;
    char * file_head = NULL; // head of read file

    for (int i = 0; i < loop_num; i++) {
        // mmap 6th arg must be a multiple of the paging size.
        file_mmap = (char *)mmap(0, page_size, PROT_READ, MAP_PRIVATE, fd, i*page_size);
        if (i == 0) file_head = file_mmap;
        file_mmap += page_size;
    }

    printf("%s\n",file_head);

    munmap(file_mmap, file_size);
    close(fd);

    return 0;
}