From 72dbf969f5369d05528d502231ef2f6103949011 Mon Sep 17 00:00:00 2001
From: bjoernf <bjoern.foersterling@web.de>
Date: Sat, 2 Sep 2023 15:18:13 +0200
Subject: [PATCH] dont append to the end but seek END:VCALENDAR

---
 src/Makefile       |  5 -----
 src/insert_event.c | 26 +++++++++++++++++++++++++-
 src/insert_event.h |  1 +
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/src/Makefile b/src/Makefile
index d8b836f..be7b47e 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -21,11 +21,6 @@ main.o: main.c
 all:
 	gcc -Wall *.c
 
-.PHONY:debug
-debug:
-	gcc -Wall -g *.c
-	gdb a.out
-
 .PHONY:run
 run:
 	gcc -Wall *.c
diff --git a/src/insert_event.c b/src/insert_event.c
index 75bbace..03ce9ea 100644
--- a/src/insert_event.c
+++ b/src/insert_event.c
@@ -6,7 +6,7 @@
 #include <unistd.h>
 
 void insert_event(char *file_name) {
-	int myfd = open(file_name, O_APPEND | O_WRONLY);
+	int myfd = open(file_name, O_RDWR);
 
 	char summary_buf[256] = "SUMMARY:";
 
@@ -24,10 +24,34 @@ void insert_event(char *file_name) {
 	summary_buf[strlen(summary_buf)-1] = '\r';
 	summary_buf[strlen(summary_buf)] = '\n';
 
+	seek_cal_end(myfd);
 	write(myfd, "BEGIN:VEVENT\r\n", strlen("BEGIN:VEVENT\r\n"));
 	write(myfd, summary_buf, strlen(summary_buf));
+	write(myfd, "END:VCALENDAR\r\n", strlen("END:VCALENDAR\r\n"));
 
 	close(myfd);
 
 	exit(0);
 }
+
+void seek_cal_end(int fd) {
+	char search_string[] = "END:VCALENDAR";
+	int j = 0;
+	char char_reader = '\0';
+
+	lseek(fd, -1, SEEK_END);
+
+	while(read(fd, &char_reader, 1)) {
+		// no need to compare to the null terminator of the search_string
+		if (char_reader == search_string[strlen(search_string)-j-1]) {
+			j++;
+		} else {
+			j = 0;
+		}
+		if (j == (strlen(search_string))) {
+			lseek(fd, -1, SEEK_CUR);
+			break;
+		}
+		lseek(fd, -2, SEEK_CUR);
+	}
+}
diff --git a/src/insert_event.h b/src/insert_event.h
index 563dec0..4719351 100644
--- a/src/insert_event.h
+++ b/src/insert_event.h
@@ -1,3 +1,4 @@
 #pragma once
 
 void insert_event(char *file_name);
+void seek_cal_end(int fd);