From 0b2396e157bbe9618a409b670cb4099956726ae3 Mon Sep 17 00:00:00 2001
From: pajjilykk <pgoldendragon@gmail.com>
Date: Sat, 4 Oct 2025 19:08:29 +0700
Subject: [PATCH] lab1 v2

---
 lab_1/in.txt   |   5 ++
 lab_1/task12.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 140 insertions(+)
 create mode 100644 lab_1/in.txt

diff --git a/lab_1/in.txt b/lab_1/in.txt
new file mode 100644
index 0000000..2d15f49
--- /dev/null
+++ b/lab_1/in.txt
@@ -0,0 +1,5 @@
+abbaabbaabbaabbaabbaabbaabbaabba
+xyzx
+ ..
+.. ./.
+----
diff --git a/lab_1/task12.c b/lab_1/task12.c
index e69de29..25a8091 100644
--- a/lab_1/task12.c
+++ b/lab_1/task12.c
@@ -0,0 +1,135 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#define RBUFSZ 4096
+#define WBUFSZ 4096
+
+static void die_perror(const char *what, const char *path, int exit_code) {
+    int saved = errno;
+    char msg[512];
+    if (path) {
+        snprintf(msg, sizeof(msg), "%s: %s: %s\n", what, path, strerror(saved));
+    } else {
+        snprintf(msg, sizeof(msg), "%s: %s\n", what, strerror(saved));
+    }
+    (void) write(STDERR_FILENO, msg, strlen(msg));
+    _exit(exit_code);
+}
+
+static long long parse_ll(const char *s) {
+    char *end = NULL;
+    errno = 0;
+    long long v = strtoll(s, &end, 10);
+    if (errno != 0 || end == s || *end != '\0' || v < 0) {
+        errno = EINVAL;
+        return -1;
+    }
+    return v;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 4) {
+        const char *usage =
+                "Usage: lab1_var12 <input.txt> <output.txt> <max_replacements>\n"
+                "Variant 12: per line, take the first character as key and replace its matches with spaces,\n"
+                "            stopping after <max_replacements> replacements globally.\n";
+        (void) write(STDERR_FILENO, usage, strlen(usage));
+        return -1;
+    }
+
+    const char *in_path = argv[1];
+    const char *out_path = argv[2];
+    long long cap = parse_ll(argv[3]);
+    if (cap < 0) {
+        die_perror("invalid max_replacements", argv[3], -1);
+    }
+
+    int in_fd = open(in_path, O_RDONLY);
+    if (in_fd < 0) {
+        die_perror("open input failed", in_path, -1);
+    }
+
+    mode_t filePerms = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH; /* rw-rw-rw- */
+    int out_fd = open(out_path, O_CREAT | O_WRONLY | O_TRUNC, filePerms);
+    if (out_fd < 0) {
+        die_perror("open output failed", out_path, -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; /* flips to 0 when cap reached */
+
+    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; /* hit the cap; from now on just copy */
+                        }
+                    } else {
+                        replacing_enabled = 0;
+                    }
+                }
+
+                if (wlen == sizeof(wbuf)) {
+                    ssize_t wrote = write(out_fd, wbuf, wlen);
+                    if (wrote < 0 || (size_t) wrote != wlen) {
+                        die_perror("write failed", out_path, -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) {
+                    die_perror("write failed", out_path, -1);
+                }
+                wlen = 0;
+            }
+            break;
+        } else {
+            die_perror("read failed", in_path, -1);
+        }
+    }
+
+    if (close(in_fd) < 0) {
+        die_perror("close input failed", in_path, -1);
+    }
+    if (close(out_fd) < 0) {
+        die_perror("close output failed", out_path, -1);
+    }
+
+    char res[64];
+    int m = snprintf(res, sizeof(res), "%lld\n", total_replacements);
+    if (m > 0) {
+        (void) write(STDOUT_FILENO, res, (size_t) m);
+    }
+
+    return 0;
+}