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


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

    int file = open(argv[1], O_RDWR | O_CREAT | O_TRUNC,
                    S_IWUSR | S_IRUSR, 0);
    if (file == -1) {
        fprintf(stderr, "error opening file info: %s \n", strerror(errno));
        return 1;
    }

    size_t rows = atoi(argv[2]);
    size_t cols = atoi(argv[3]);

    off_t file_size = sizeof(uint32_t) * cols * rows;
    if(ftruncate(file, file_size)) {
        fprintf(stderr, "not enough space on disk\n");
        return 1;
    }

    unsigned long matrix[100][100];
    unsigned long num = 1;
    /*  k - starting row index
        m - ending row index
        l - starting column index
        n - ending column index */
    size_t k = 0, l = 0;
    while (k < rows && l < cols)
    {
        for (size_t i = l; i < cols; ++i)
            matrix[k][i] = num++;

        k++;

        for (size_t i = k; i < rows; ++i)
            matrix[i][cols - 1] = num++;
        cols--;

        if (k < rows)
        {
            for (size_t i = cols - 1; i >= l; --i)
                matrix[rows - 1][i] = num++;
            rows--;
        }

        if (l < cols)
        {
            for (size_t i = rows - 1; i >= k; --i)
                matrix[i][l] = num++;
            l++;
        }
    }


    void *mapped = mmap(
            NULL,
            file_size,
            PROT_READ,
            MAP_PRIVATE,
            file,
            0
    );

    uint32_t * data = mapped;

    rows = atoi(argv[2]);
    cols = atoi(argv[3]);
    // matrix -> file ??
    for (size_t i = 0; i < rows; i++) {
        for (size_t j = 0; j < cols; j++) {
            data[i][j] = matrix[i][j];
        }
    }

    munmap(mapped, file_size);
    close(file);
    return 0;
}