draw cursor at newline linebreaks (only \n though and not \r\n)

fcore/cursor.sml

@@ -1,51 +1,58 @@
 structure Cursor =
 struct
-  (* Prerequisite: lineGap is moved to requested idx first *)
-  fun viL (lineGap: LineGap.t, cursorIdx) =
-    let
-      val {rightStrings, idx = bufferIdx, ...} = lineGap
-    in
-      case rightStrings of
-        hd :: tl =>
-          let
-            (* idx relative to this string *)
-            val strIdx = cursorIdx - bufferIdx
-          in
-            if strIdx < String.size hd - 2 then
-              (* increment if there is a character after where cursor is 
-               * but first, check if we are in a \r\n pair; 
-               * if we are, then increment cursor by 2 *)
-              if
-                String.size hd > strIdx + 2
-                andalso String.sub (hd, strIdx + 1) = #"\r"
-                andalso String.sub (hd, strIdx + 2) = #"\n"
-              then
-                (* increment cursor by 2 if we are inside \r\n pair *)
-                cursorIdx + 2
+  (* todo: viL does not handle \r\n pair right now
+   * but this is not a priority so it's okay *)
+  local
+    fun helpVilLf (hd, strIdx, bufferIdx, cursorIdx, tl) =
+      (* if we are in \n, 
+       * move cursor to character after newline 
+       * if possible *)
+      if strIdx < String.size hd - 3 then
+        (* we know it is safe to move cursorIdx by 2 
+         * if strIdx + 2 is before or at the end of the string. *)
+        cursorIdx + 2
+      else
+        (* we have to check the tl to see if it is not empty  
+         * so we know it is safe to move. *)
+        case tl of
+          _ :: _ => 
+            (* not empty, so we can increment by 2 *) 
+            cursorIdx + 2
+        | [] =>
+            (* empty, so return end of string which is \n *)
+            bufferIdx + String.size hd - 1
+  in
+    (* Prerequisite: lineGap is moved to requested idx first 
+     * todo: check if we are in a \r\n pair, but this is not a priority *)
+    fun viL (lineGap: LineGap.t, cursorIdx) =
+      let
+        val {rightStrings, idx = bufferIdx, ...} = lineGap
+      in
+        case rightStrings of
+          hd :: tl =>
+            let
+              (* convert absolute cursorIdx to idx relative to hd string *)
+              val strIdx = cursorIdx - bufferIdx
+            in
+              if strIdx < String.size hd - 2 then
+                (case String.sub (hd, strIdx + 1) of
+                   #"\n" => helpVilLf (hd, strIdx, bufferIdx, cursorIdx, tl)
+                 | _ => cursorIdx + 1)
               else
-                (* inccrement cursor by 1 if we are not inside \r\n pair *)
-                cursorIdx + 1
-            else
-              (case tl of
-                 _ :: _ =>
-                   (* if there is another string after current head, we can increment cursorIdx 
-                    * however, first we need to check if next string is \r\n pair. *)
-                   if
-                     String.size hd > strIdx + 2
-                     andalso String.sub (hd, strIdx + 1) = #"\r"
-                     andalso String.sub (hd, strIdx + 2) = #"\n"
-                   then
-                     (* increment cursor by 2 if we are inside \r\n pair *)
-                     cursorIdx + 2
-                   else
-                     (* inccrement cursor by 1 if we are not inside \r\n pair *)
-                     cursorIdx + 1
-               | _ =>
-                   (* if there is no string after current head, return original cursorIdx *)
-                   cursorIdx)
-          end
-      | [] =>
-          (* return original cursorIdx if there is nothing to the right *)
-          cursorIdx
-    end
+                (case tl of
+                   tlhd :: tltl =>
+                     (* if there is another string after current head, we can increment cursorIdx 
+                      * however, first we need to check if next char is \n. *)
+                     (case String.sub (tlhd, 0) of
+                        #"\n" => helpVilLf (tlhd, 0, bufferIdx, cursorIdx, tltl)
+                      | _ => cursorIdx + 1)
+                 | _ =>
+                     (* if there is no string after current head, return original cursorIdx *)
+                     cursorIdx)
+            end
+        | [] =>
+            (* return original cursorIdx if there is nothing to the right *)
+            cursorIdx
+      end
+  end
 end

fcore/text-builder.sml

@@ -316,11 +316,25 @@ struct
             )
       | #"\n" =>
           if posY + ySpace < windowHeight then
-            buildTextStringWithinCursor
-              ( pos + 1, str, acc, startX, posY + ySpace, startX
-              , windowWidth, windowHeight, fWindowWidth, fWindowHeight
-              , r, g, b, tl, absIdx + 1, cursorPos, cursorAcc, hr, hg, hb
-              )
+            if absIdx <> cursorPos then
+              (* not in cursor position, so iterate like normal *)
+              buildTextStringWithinCursor
+                ( pos + 1, str, acc, startX, posY + ySpace, startX
+                , windowWidth, windowHeight, fWindowWidth, fWindowHeight
+                , r, g, b, tl, absIdx + 1, cursorPos, cursorAcc, hr, hg, hb
+                )
+            else
+              (* in cursor position, so build cursorAcc 
+               * and call AfterCursor function *)
+              let
+                val cursorAcc = buildCursor (posX, posY, fWindowWidth, fWindowHeight, r, g ,b)
+              in
+                buildTextStringAfterCursor
+                  ( pos + 1, str, acc, startX, posY + ySpace, startX
+                  , windowWidth, windowHeight, fWindowWidth, fWindowHeight
+                  , r, g, b, tl, cursorAcc
+                  )
+              end
           else
             accToDrawMsg (acc, cursorAcc)
       | #"\r" =>