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

#define RBUFSZ 4096
#define WBUFSZ 4096

// Функция обработки текста
long long process_text(const char *in_path, const char *out_path, long long cap) {
    int in_fd = open(in_path, O_RDONLY);
    if (in_fd < 0) {
        return -1;
    }

    mode_t filePerms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
    int out_fd = open(out_path, O_CREAT | O_WRONLY | O_TRUNC, filePerms);
    if (out_fd < 0) {
        close(in_fd);
        return -1;
    }

    char rbuf[RBUFSZ];
    char wbuf[WBUFSZ];
    size_t wlen = 0;

    long long total_replacements = 0;
    int at_line_start = 1;
    unsigned char line_key = 0;
    int replacing_enabled = 1;

    for (;;) {
        ssize_t n = read(in_fd, rbuf, sizeof(rbuf));
        if (n > 0) {
            for (ssize_t i = 0; i < n; i++) {
                unsigned char c = (unsigned char) rbuf[i];

                if (at_line_start) {
                    line_key = c;
                    at_line_start = 0;
                }

                unsigned char outc = c;
                if (c == '\n') {
                    at_line_start = 1;
                } else if (replacing_enabled && c == line_key) {
                    if (total_replacements < cap) {
                        outc = ' ';
                        total_replacements++;
                        if (total_replacements == cap) {
                            replacing_enabled = 0;
                        }
                    } else {
                        replacing_enabled = 0;
                    }
                }

                if (wlen == sizeof(wbuf)) {
                    ssize_t wrote = write(out_fd, wbuf, wlen);
                    if (wrote < 0 || (size_t) wrote != wlen) {
                        close(in_fd);
                        close(out_fd);
                        return -1;
                    }
                    wlen = 0;
                }
                wbuf[wlen++] = (char) outc;
            }
        } else if (n == 0) {
            if (wlen > 0) {
                ssize_t wrote = write(out_fd, wbuf, wlen);
                if (wrote < 0 || (size_t) wrote != wlen) {
                    close(in_fd);
                    close(out_fd);
                    return -1;
                }
                wlen = 0;
            }
            break;
        } else {
            close(in_fd);
            close(out_fd);
            return -1;
        }
    }

    close(in_fd);
    close(out_fd);

    return total_replacements;
}