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

#define MAX_LINE 4096

int replace_char(char *buf, int key, int *replacements_left);

int main(int argc, char *argv[]) {
    if (argc != 4) {
        fprintf(stderr, "Usage: %s <in> <out> <cap>\n", argv[0]);
        return 1;
    }

    FILE *fin = fopen(argv[1], "r");
    if (!fin) { perror("fopen input"); return 1; }
    FILE *fout = fopen(argv[2], "w");
    if (!fout) { perror("fopen output"); fclose(fin); return 1; }

    int cap = atoi(argv[3]);
    if (cap < 0) {
        fprintf(stderr, "invalid cap\n");
        fclose(fin);
        fclose(fout);
        return 1;
    }

    int total = 0;
    char line[MAX_LINE];

    while (fgets(line, sizeof(line), fin)) {
        if (cap > 0) {
            // key is unused, but pass the first byte for symmetry
            int key = (unsigned char)line[0];
            int repl_line = replace_char(line, key, &cap);
            total += repl_line;
        }
        fputs(line, fout);
    }

    fclose(fin);
    fclose(fout);
    printf("total_replacements: %d\n", total);
    return 0;
}