From a21f759d2344b8de28faa36fe7ca8689689df3e8 Mon Sep 17 00:00:00 2001
From: Francesco <inbox@francescorocca.me>
Date: Mon, 8 Sep 2025 02:48:47 +0200
Subject: [PATCH] feat: string find

---
 string/mystring.c  | 56 +++++++++++++++++++++++++++++++++++++++++++++-
 string/mystring.h  |  2 --
 test/string/str2.c |  4 ++++
 3 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/string/mystring.c b/string/mystring.c
index 4a89832..89dd82d 100644
--- a/string/mystring.c
+++ b/string/mystring.c
@@ -239,7 +239,7 @@ char *mcl_string_cstr(mcl_string_s *string) {
 	tl_buffer_s *tb = (tl_buffer_s *)tss_get(buffer_key);
 	if (tb == NULL) {
 		/* Not found, make a new one */
-		tb = malloc(sizeof(*tb));
+		tb = malloc(sizeof(tl_buffer_s));
 		if (tb == NULL) {
 			mtx_unlock(&string->lock);
 
@@ -352,3 +352,57 @@ void mcl_string_tolower(mcl_string_s *string) {
 
 	mtx_unlock(&string->lock);
 }
+
+/* Build Longest Prefix Suffix array */
+static void build_lsp(int *lps, const char *substring, size_t sub_len) {
+	int len = 0;
+	int i = 1;
+
+	while (i < sub_len) {
+		if (substring[i] == substring[len]) {
+			lps[i++] = ++len;
+		} else {
+			if (len != 0) {
+				len = lps[len - 1];
+			} else {
+				lps[i++] = 0;
+			}
+		}
+	}
+}
+
+int mcl_string_find(mcl_string_s *string, const char *substring) {
+	if (string == NULL || substring == NULL) {
+		return -1;
+	}
+
+	/* Handle empty case */
+	if (strcmp(string->data, "") == 0) {
+		return -1;
+	}
+
+	size_t sub_len = strlen(substring);
+	int lps[sub_len];
+	memset(lps, 0, sizeof(lps));
+	build_lsp(lps, substring, sub_len);
+
+	size_t i = 0; /* string iterator */
+	size_t j = 0; /* substring iterator */
+	while (i < string->size) {
+		if (string->data[i] == substring[j]) {
+			i++;
+			j++;
+			if (j == sub_len) {
+				return i - j;
+			}
+		} else {
+			if (j != 0) {
+				j = lps[j - 1];
+			} else {
+				i++;
+			}
+		}
+	}
+
+	return -1;
+}
diff --git a/string/mystring.h b/string/mystring.h
index 3dbbce5..1851249 100644
--- a/string/mystring.h
+++ b/string/mystring.h
@@ -111,8 +111,6 @@ void mcl_string_tolower(mcl_string_s *string);
  * @param string String where to search.
  * @param substring Substring to search.
  * @return Index of the first occurrence, -1 on failure.
- *
- * @note TODO
  */
 int mcl_string_find(mcl_string_s *string, const char *substring);
 
diff --git a/test/string/str2.c b/test/string/str2.c
index 564cfae..183d292 100644
--- a/test/string/str2.c
+++ b/test/string/str2.c
@@ -28,6 +28,10 @@ void test_str2(void) {
 	assert(mcl_string_length(s1) == 50);
 	assert(mcl_string_capacity(s1) == 64);
 
+	/* Find substring in string */
+	int pos = mcl_string_find(s1, "is");
+	assert(pos == 2);
+
 	mcl_string_free(s1);
 	mcl_string_free(s2);
 	mcl_string_free(extend_me);