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

void deplacerPremierOctet(const char *filename) {
    FILE *file;
    unsigned char first_byte;
    long file_size;
    unsigned char *buffer;


    file = fopen(filename, "r+b");
    if (file == NULL) {
        perror("Erreur d'ouverture");
        exit(EXIT_FAILURE);
    }

    if (fread(&first_byte, 1, 1, file) != 1) {
        perror("Erreur de lecture");
        fclose(file);
        exit(EXIT_FAILURE);
    }

    fseek(file, 0, SEEK_END);
    if (fwrite(&first_byte, 1, 1, file) != 1) {
        perror("Erreur d'écriture");
        fclose(file);
        exit(EXIT_FAILURE);
    }

    file_size = ftell(file);
    fclose(file);

    file = fopen(filename, "r+b");
    if (file == NULL) {
        perror("Erreur d'ouverture");
        exit(EXIT_FAILURE);
    }

    buffer = (unsigned char *)malloc(file_size - 1);
    if (buffer == NULL) {
        perror("Erreur d'allocation mémoire");
        fclose(file);
        exit(EXIT_FAILURE);
    }

    fseek(file, 1, SEEK_SET);
    if (fread(buffer, 1, file_size - 1, file) != file_size - 1) {
        perror("Erreur de lecture");
        free(buffer);
        fclose(file);
        exit(EXIT_FAILURE);
    }
    fclose(file);

    file = fopen(filename, "wb");
    if (file == NULL) {
        perror("Erreur d'ouverture");
        free(buffer);
        exit(EXIT_FAILURE);
    }

    if (fwrite(buffer, 1, file_size - 1, file) != file_size - 1) {
        perror("Erreur d'écriture");
        free(buffer);
        fclose(file);
        exit(EXIT_FAILURE);
    }

    if (fwrite(&first_byte, 1, 1, file) != 1) {
        perror("Erreur d'écriture");
        free(buffer);
        fclose(file);
        exit(EXIT_FAILURE);
    }

    free(buffer);
    fclose(file);

    printf("Modification effectuée.\n");
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <toto.c>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    deplacerPremierOctet(argv[1]);
    return 0;
}