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

int main(int argc, char *argv[])
{
    // first check to see if what user entered made sense:
    if (argc != 2)
    {
        fprintf(stderr, "Usage: copy infile outfile \n");
        return 1;
    }

    // remember filenames
    char *infile = argv[1];    // for my own edification: store argv[1] in a char array whose address we shall call "infile"

    // open input file
    FILE *inptr = fopen(infile, "r");  // for my own edification: fopen returns the address of the input file (NOT of its name). We declare that to be the address (called "inptr") of a FILE.
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 2;
    }

    int counter = 0; // will keep track of how many jpgs we've found so far, will use in file names

    unsigned char current_block[512];  // since each unsigned char is 1 byte and we want to read 512 bytes at a time
    char current_out_name[8]; // xxx.jpg is seven chars, plus \0 makes eight total
    FILE *img = NULL;


    while (1) // this loop finds and writes the first 512B block of our first jpg
    {
        fread(current_block, 512, 1, inptr); // read 1 512B block starting at address inptr and put into current_block called "current_block"

        if (current_block[0] == 0xff && current_block[1] == 0xd8 && current_block[2] == 0xff && (current_block[3] & 0xf0) == 0xe0) // from Zamyla (tells us if we're at start of jpg)
        {
            sprintf(current_out_name, "%03i.jpg", counter); // make a string that will eventually be the name of current output file
            img = fopen(current_out_name, "w"); // give ourselves permission to write into file for our first image
            fwrite(current_block, 512, 1, img); // write 1 512B block taken from inptr onto current_out_name, the output file w/ which we're working
            counter++;
            break;
        }
    }

    while (fread(current_block, 512, 1, inptr) == 1) // while there remains at least one whole 512B block left in the file
    {
        if (current_block[0] == 0xff && current_block[1] == 0xd8 && current_block[2] == 0xff && (current_block[3] & 0xf0) == 0xe0) // from Zamyla
        {
            // close the old file and write the next 512 bytes into the new file (we've already incremented counter)
            fclose(img);
            sprintf(current_out_name, "%03i.jpg \n", counter); // make a string that will eventually be the name of new output file
            img = fopen(current_out_name, "w"); // give ourselves permission to write into file for next image
            fwrite(current_block, 512, 1, img); // write 1 512B block taken from inptr onto current_out_name, the output file w/ which we're working
            counter++;
        }
        else
        {
            fwrite(current_block, 512, 1, img);
        }

    }
    fclose(img);
}