more string fns

all.h

@@ -345,8 +345,8 @@ typedef struct Codepoint {
 } Codepoint;
 
 typedef struct TextPos {
-  i64 line;
-  i64 column;
+  u32 line;
+  u32 column;
 } TextPos;
 
 typedef struct TextRange {
@@ -680,6 +680,9 @@ fn String stringFromRawCodepoint(Arena* a, u32 c);
 fn bool stringInsertCodepointAtByte(String* s, Codepoint c, u32 byte_offset, bool keep_trailing_zero);
 fn u8 stringDeleteCodepointAtByte(String* s, u32 byte_offset);
 fn bool stringDeleteCodepointsBetweenByteOffsetsInclusive(String* s, u32 start, u32 end);
+fn u32 stringCountLines(String s);
+fn u32 stringLineLen(String s, u32 line_number);
+fn u32 stringLineStartByteOffset(String s, u32 line_number);
 
 ///// OS-wrapped apis
 void      osInit();

string.c

@@ -428,3 +428,41 @@ fn StringUTF16Const str16FromStr8(Arena* arena, String string) {
 	return result;
 }
 
+fn u32 stringCountLines(String s) {
+  u32 result = 1;
+  for (u32 i = 0; i < s.length; i++) {
+    if (s.bytes[i] == '\n') {
+      result += 1;
+    }
+  }
+  return result;
+}
+
+fn u32 stringLineLen(String s, u32 line_number) {
+  u32 result = 0;
+  u32 current_line = 0;
+  for (u32 i = 0; i < s.length && current_line <= line_number; i++) {
+    if (current_line == line_number) {
+      result += 1;
+    }
+    if (s.bytes[i] == '\n') {
+      current_line += 1;
+    }
+  }
+  return result;
+}
+
+fn u32 stringLineStartByteOffset(String s, u32 line_number) {
+  u32 current_line = 0;
+  for (u32 i = 0; i < s.length; i++) {
+    // do this check first, so we won't return '\n' character pos, but the following char pos
+    if (current_line == line_number) {
+      return i;
+    }
+    if (s.bytes[i] == '\n') {
+      current_line += 1;
+    }
+  }
+  return s.length;
+}
+