rename cursor.sml's 'clipIdxAfterDelete' function to 'clipIdx', simplify it, and use it in other functions too

fcore/app-update.sml

@@ -101,12 +101,13 @@ struct
       val {line = bufferLine, idx = bufferIdx, ...} = buffer
 
       val bufferIdx = bufferIdx - 1
+      val bufferIdx = Cursor.clipIdx (buffer, bufferIdx)
       val bufferLine = bufferLine - 1
 
       val buffer = LineGap.goToIdx (bufferIdx, buffer)
       val bufferLine = 
         let
-          val maxHeight = windowHeight - (TextConstants.ySpace * 2)
+          val maxHeight = windowHeight - TextConstants.ySpace
         in
           TextWindow.getStartLineWithCursorCentered 
             (buffer, bufferIdx, bufferLine, windowWidth, maxHeight)
@@ -159,6 +160,7 @@ struct
       let
         val buffer = LineGap.goToIdx (cursorIdx, buffer)
         val cursorIdx = fMove (buffer, cursorIdx)
+        val cursorIdx = Cursor.clipIdx (buffer, cursorIdx)
       in
         helpMove (app, buffer, cursorIdx, count - 1, fMove)
       end
@@ -258,6 +260,7 @@ struct
         (* move LineGap to cursorIdx, which is necessary for finding newCursorIdx *)
         val buffer = LineGap.goToIdx (cursorIdx, buffer)
         val cursorIdx = fMove (buffer, cursorIdx, chr)
+        val cursorIdx = Cursor.clipIdx (buffer, cursorIdx)
       in
         helpMoveToChr (app, buffer, cursorIdx, count - 1, fMove, chr)
       end
@@ -345,7 +348,7 @@ struct
          * is no longer a valid idx,
          * clip cursorIdx to the end. *)
         val buffer = LineGap.goToIdx (cursorIdx, buffer)
-        val cursorIdx = Cursor.clipIdxAfterDelete (buffer, cursorIdx)
+        val cursorIdx = Cursor.clipIdx (buffer, cursorIdx)
       in
         buildTextAndClear (app, buffer, cursorIdx)
       end
@@ -364,13 +367,6 @@ struct
         val length = high - low
 
         val buffer = LineGap.delete (low, length, buffer)
-
-        (* todo: possibly decrement cursorIdx by 1 
-         * if deleting put cursorIdx past end of file.
-         * else, if deleting put cursorIdx before 0,
-         * ensure that it is clipped to 0.
-         * else, leave cursorIdx alone.
-         * *)
       in
         helpDelete (app, buffer, low, count - 1, fMove)
       end

fcore/cursor.sml

@@ -1595,7 +1595,7 @@ struct
             val lineIdx = Vector.sub (lhd, relativeLine)
           in
             if lineIdx = String.size shd - 1 andalso List.null stl then
-              (* if is end of buffer, return last idx in buffer; * else, 
+              (* if is end of buffer, return last idx in buffer; else, 
                * increment by 1 as we want to go to first char after line break *)
               bufferIdx + lineIdx
             else
@@ -1715,33 +1715,36 @@ struct
     end
 
   (* Prerequisite: lineGap is moved to cursorIdx *)
-  fun clipIdxAfterDelete (lineGap: LineGap.t, cursorIdx) =
+  fun clipIdx (lineGap: LineGap.t, cursorIdx) =
     let
       val {rightStrings, idx = bufferIdx, ...} = lineGap
     in
+      (* We are trying to check if cursorIdx is within the buffer. *)
       case rightStrings of
-        hd :: tl =>
+        _ :: _ :: _ => 
+          (* if there is a string after the hd, 
+           * we are definitely in a valid idx and should return it *)
+          cursorIdx
+      | [hd] =>
           let
             val strIdx = cursorIdx - bufferIdx
           in
-            if strIdx < String.size hd then
+            if strIdx < String.size hd - 1 then
+              (* if we are before the last char in the string.
+               * Unix file endings always have \n at the end
+               * but we do not want cursor to ever go to end
+               * as vi also does not go to the very end.
+               * This is why we check strIdx is before the last char. 
+               * *)
               cursorIdx
             else
-              (* strIdx is in tl *)
-              (case tl of
-                tlhd :: tltl =>
-                let
-                  val strIdx = strIdx - String.size hd
-                in
-                  if strIdx < String.size tlhd then
-                    cursorIdx
-                  else
-                    bufferIdx + String.size hd + String.size tlhd - 1
-                end
-              | [] =>
-                  bufferIdx + String.size hd - 1)
+              (* if end of buffer - 2 is greater than 0, then that;
+               * else, 0 *)
+              Int.max (bufferIdx + String.size hd - 2, 0)
           end
-      | [] =>
-          Int.max (bufferIdx - 1, 0)
+      | [] => 
+          (* if end of buffer - 2 is greater than 0, then that;
+           * else, 0 *)
+          Int.max (bufferIdx - 2, 0)
     end
 end