From ac49710a12a44a7c6ac618d82c5c685b473b1cd2 Mon Sep 17 00:00:00 2001
From: Jaroslav Louma <jaroslav.louma.ml@gmail.com>
Date: Wed, 29 Nov 2023 21:14:18 +0100
Subject: [PATCH] Added `String_charAt` + tests

---
 include/internal/String.h   |  9 +++++++++
 src/internal/String.c       | 13 +++++++++++++
 test/internal/String.test.c | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 57 insertions(+)

diff --git a/include/internal/String.h b/include/internal/String.h
index f0138dd..1231a6a 100644
--- a/include/internal/String.h
+++ b/include/internal/String.h
@@ -105,6 +105,15 @@ bool String_endsWith(String *string, char *value);
  */
 long String_indexOf(String *string, char *value);
 
+/**
+ * Returns the character at a given index in a String.
+ *
+ * @param string The String to get the character from.
+ * @param index The index of the character to get. (negative values start from the end)
+ * @return The character at the given index.
+ */
+char String_charAt(String *string, signed long index);
+
 /**
  * Copies the contents of the String to a given buffer of a given length.
  *
diff --git a/src/internal/String.c b/src/internal/String.c
index 439c0df..091d05a 100644
--- a/src/internal/String.c
+++ b/src/internal/String.c
@@ -218,6 +218,19 @@ long String_indexOf(String *string, char *value) {
 	return result - string->value;
 }
 
+char String_charAt(String *string, signed long index) {
+	if(!string) return '\0';
+	if(!string->value) return '\0';
+
+	// Resolve negative indices
+	if(index < 0) index = string->length + index;
+
+	// Index out of bounds
+	if(index < 0 || index > (signed long)string->length) return '\0';
+
+	return string->value[index];
+}
+
 void String_copy(String *string, char *dest, size_t length) {
 	if(!string) return;
 	if(!dest) return;
diff --git a/test/internal/String.test.c b/test/internal/String.test.c
index e5e2a91..30713f2 100644
--- a/test/internal/String.test.c
+++ b/test/internal/String.test.c
@@ -521,3 +521,38 @@ DESCRIBE(fromRange, "String_fromRange") {
 		EXPECT_NULL(str);
 	})
 }
+
+DESCRIBE(charAt, "String_charAt") {
+	String *str = NULL;
+
+	TEST("Simple charAt", {
+		str = String_alloc("Hello, World!");
+		EXPECT_EQUAL_CHAR(String_charAt(str, 0), 'H');
+		EXPECT_EQUAL_CHAR(String_charAt(str, 3), 'l');
+		EXPECT_EQUAL_CHAR(String_charAt(str, 6), ' ');
+		EXPECT_EQUAL_CHAR(String_charAt(str, 9), 'r');
+		EXPECT_EQUAL_CHAR(String_charAt(str, 12), '!');
+	})
+
+	TEST("Single character charAt", {
+		str = String_alloc("A");
+		EXPECT_EQUAL_CHAR(String_charAt(str, 0), 'A');
+	})
+
+	TEST("Empty charAt", {
+		str = String_alloc("");
+		EXPECT_EQUAL_CHAR(String_charAt(str, 0), '\0');
+	})
+
+	TEST("Negative index", {
+		str = String_alloc("Hello, World!");
+		EXPECT_EQUAL_CHAR(String_charAt(str, -1), '!');
+		EXPECT_EQUAL_CHAR(String_charAt(str, -13), 'H');
+	})
+
+	TEST("Out of bounds charAt", {
+		str = String_alloc("Hello, World!");
+		EXPECT_EQUAL_CHAR(String_charAt(str, 13), '\0');
+		EXPECT_EQUAL_CHAR(String_charAt(str, -14), '\0');
+	})
+}