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

#define HEADER_SIZE 54
#define PIXEL_SIZE  3

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

    printf("Starting ...\n");

    int c = 0;
    char input[69];
    char output[21];
    char type[3];
    int keep_going = 1;
    unsigned short int bpp;
    char median = 0;
    char header_tab[HEADER_SIZE];
    char pixel_tab[PIXEL_SIZE];
    char pixel_write_tab[PIXEL_SIZE];

    FILE * fin;
    FILE * fout;
    FILE * temp;

    printf("Enter path of a bitmap image :\n");

    if(fgets(input, 69, stdin) == NULL){
        printf("Error - Unable to get input\n");
        return 1;
    }

    input[strlen(input)-1] = '\0';

    if (!(temp = fopen(input, "rb"))) {
        printf("Error - Unable to open the file given (errno:%d)\n", errno);
        return 1;
    }

    fseek(temp,0,0);
    fread(type,1,2,temp);
    type[2] = '\0';

    fseek(temp,28,0);
    fread(&bpp,1,2,temp);

    if (strcmp(type,"BM") || (bpp != 24)){
        printf("Error - The file is not BMP format or is not 24 bits\n");
        exit(0);
    }

    fin = fopen(input, "rb");

    printf("Enter a file name for output file (max 20 char) :\n");
    if(fgets(output, 20, stdin) == NULL){
        printf("Error - Unable to get output file name\n");
        return 1;
    }

    if(output == input){
        printf("Error - Input file can't be the output file !\n");
        return 1;
    }

    output[strlen(output)-1] = '\0';

    if (!(fout = fopen(output, "wb"))) {
        printf("Error - Unable to open the output file (errno:%d)\n", errno);
        fclose(fin);
        return 1;
    }

    //Read header
    c = fread(header_tab, 1, HEADER_SIZE ,fin);
    if (c<HEADER_SIZE){
        printf("Warning - Header to small\n Exiting properly ...\n");
        fclose(fin);
        fclose(fout);
        exit(1);
    }

    //Write header
    fwrite(header_tab, 1, HEADER_SIZE, fout);

    //To shade of grey
    do
    {
        c = fread(pixel_tab, 1,PIXEL_SIZE, fin);
        if (c!=3){
            keep_going = 0;
        } else {
            median = (char) ((pixel_tab[0] + pixel_tab[1] + pixel_tab[2]) / 3);
            pixel_write_tab[0] = median;
            pixel_write_tab[1] = median;
            pixel_write_tab[2] = median;
            fwrite(pixel_write_tab, 1, PIXEL_SIZE, fout);
        }
    }
    while (keep_going == 1);

    fclose(fin);
    fclose(fout);

    printf("Ending without errors\n");
    return 0;
}