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

char* func(char *src, char *repl, char *on);

int main(void)
{
	char original[] = "foobarfoofoobaraaba";
	char replace[] = "bar";
	char on[] = "yes";

	char *result = NULL;
	result = func(original, replace, on);

	printf("%s\n", result);

	return 0;
}

char* func(char *src, char *repl, char *on)
{
	int src_len = strlen(src);
	int repl_len = strlen(repl);
	int on_len = strlen(on);
	char *result = malloc((src_len + 1) * sizeof(char));
	if (result == NULL) {
		printf("malloc error\n");
		exit(-1);
	}
	strcpy(result, src);

	for (int i = 0; i < src_len - repl_len; i++) {

		int found = 1;
		for (int j = 0; j < repl_len; j++) {
			if (result[i + j] != repl[j]) {
				found = 0;
				break;
			}
		}

		if (found) {
			if (repl_len == on_len) {
				memcpy(&result[i], on, on_len);
			} else if (repl_len > on_len) {
				memcpy(&result[i], on, on_len);
				memmove(&result[i + on_len], &result[i + repl_len], src_len - i + repl_len);
				char *temp = realloc(result, src_len + (on_len - repl_len));
				if (temp == NULL) {
					printf("src realloc error!\n");
					exit(-1);
				}
				result = temp;
				src_len += (on_len - repl_len);
			} else {
				char *temp = realloc(result, (src_len + on_len + 1) * sizeof(char));
				if (temp == NULL) {
					printf("src realloc error!\n");
					exit(-1);
				}
				result = temp;
				src_len += on_len;
				memmove(&result[i + repl_len - 1], &result[i], src_len - i);
				memcpy(&result[i], on, on_len);
			}

		}
	}

	return result;
}