add cursorIdx to app type in fcore

fcore/app-type.sml

@@ -1,12 +1,18 @@
 structure AppType =
 struct
   type app_type =
-    {buffer: LineGap.t, windowWidth: int, windowHeight: int, startLine: int}
+    { buffer: LineGap.t
+    , windowWidth: int
+    , windowHeight: int
+    , startLine: int
+    , cursorIdx: int
+    }
 
   fun init (buffer, windowWidth, windowHeight) : app_type =
     { buffer = buffer
     , windowWidth = windowWidth
     , windowHeight = windowHeight
     , startLine = 0
+    , cursorIdx = 0
     }
 end

fcore/app-update.sml

@@ -8,10 +8,9 @@ struct
 
   fun resizeText (app: app_type, newWidth, newHeight) =
     let
-      val {buffer, windowWidth, windowHeight, startLine} = app
+      val {buffer, windowWidth, windowHeight, startLine, cursorIdx} = app
 
       val newBuffer = LineGap.goToLine (startLine, buffer)
-      val cursorIdx = 0 (* TEMP *)
       val textVec = TextBuilder.build
         (startLine, cursorIdx, newBuffer, newWidth, newHeight)
 

fcore/app-with.sml

@@ -4,12 +4,14 @@ struct
 
   fun bufferAndSize (app: app_type, newBuffer, newWidth, newHeight) =
     let
-      val {buffer = _, windowWidth = _, windowHeight = _, startLine} = app
+      val {buffer = _, windowWidth = _, windowHeight = _, startLine, cursorIdx} =
+        app
     in
       { buffer = newBuffer
       , windowWidth = newWidth
       , windowHeight = newHeight
       , startLine = startLine
+      , cursorIdx = cursorIdx
       }
     end
 end