pass 'maxLength' value to TextScroll function so that we can prevent scrolling past the bottom of the file (unless we want to od so by centtering the screen)

fcore/normal-mode/normal-finish.sml

@@ -29,7 +29,8 @@ struct
 
       val cursorLine = LineGap.idxToLineNumber (cursorIdx, buffer)
       val startLine =
-        TextScroll.getStartLine (prevLineNumber, cursorLine, windowHeight)
+        TextScroll.getStartLine
+          (prevLineNumber, cursorLine, windowHeight, #lineLength buffer)
 
       (* move buffer to new startLine as required by TextBuilder.build *)
       val buffer = LineGap.goToLine (startLine, buffer)

fcore/normal-mode/normal-move.sml

@@ -74,7 +74,8 @@ struct
           (buffer, bufferIdx, windowWidth, prevScrollColumn)
 
       val bufferLine =
-        TextScroll.getStartLine (prevLineNumber, bufferLine, windowHeight)
+        TextScroll.getStartLine
+          (prevLineNumber, bufferLine, windowHeight, #lineLength buffer)
       val buffer = LineGap.goToLine (bufferLine, buffer)
 
       val drawMsg = NormalModeTextBuilder.build
@@ -129,6 +130,11 @@ struct
 
       val buffer = LineGap.goToIdx (lineIdx, buffer)
       val endOfLineIdx = Cursor.viDlr (buffer, lineIdx, 1)
+      val endOfLineIdx =
+        if endOfLineIdx >= #textLength buffer - 2 then
+          Int.max (0, #textLength buffer - 2)
+        else
+          endOfLineIdx
 
       val cursorIdx = Int.min (endOfLineIdx, lineIdx + column)
 
@@ -141,7 +147,11 @@ struct
 
       val startLine =
         TextScroll.getStartLine
-          (prevLineNumber, newCursorLineNumber, windowHeight)
+          ( prevLineNumber
+          , newCursorLineNumber
+          , windowHeight
+          , #lineLength buffer
+          )
 
       val buffer = LineGap.goToLine (startLine, buffer)
 
@@ -223,7 +233,7 @@ struct
       val newCursorLineNumber = cursorLineNumber + count
       val newCursorLineNumber =
         if cursorLineNumber >= #lineLength buffer - 2 then
-          Int.max (0, #lineLength buffer - 2)
+          Int.max (0, #lineLength buffer - 1)
         else
           newCursorLineNumber
     in
@@ -270,7 +280,8 @@ struct
 
           val cursorLine = LineGap.idxToLineNumber (cursorIdx, buffer)
           val startLine =
-            TextScroll.getStartLine (prevLineNumber, cursorLine, windowHeight)
+            TextScroll.getStartLine
+              (prevLineNumber, cursorLine, windowHeight, #lineLength buffer)
 
           val buffer = LineGap.goToLine (startLine, buffer)
 
@@ -331,7 +342,8 @@ struct
 
         val cursorLine = LineGap.idxToLineNumber (cursorIdx, buffer)
         val startLine =
-          TextScroll.getStartLine (prevLineNumber, cursorLine, windowHeight)
+          TextScroll.getStartLine
+            (prevLineNumber, cursorLine, windowHeight, #lineLength buffer)
 
         val buffer = LineGap.goToLine (startLine, buffer)
 

fcore/normal-mode/normal-search-finish.sml

@@ -52,7 +52,8 @@ struct
       val buffer = LineGap.goToIdx (cursorIdx, buffer)
       val cursorLine = LineGap.idxToLineNumber (cursorIdx, buffer)
       val startLine =
-        TextScroll.getStartLine (prevLineNumber, cursorLine, windowHeight)
+        TextScroll.getStartLine
+          (prevLineNumber, cursorLine, windowHeight, #lineLength buffer)
       val buffer = LineGap.goToLine (startLine, buffer)
 
       val remainingWindowHeight = windowHeight - (TextConstants.ySpace * 2)
@@ -122,7 +123,8 @@ struct
       val buffer = LineGap.goToIdx (cursorIdx, buffer)
       val cursorLine = LineGap.idxToLineNumber (cursorIdx, buffer)
       val startLine =
-        TextScroll.getStartLine (prevLineNumber, cursorLine, newWindowHeight)
+        TextScroll.getStartLine
+          (prevLineNumber, cursorLine, newWindowHeight, #lineLength buffer)
       val buffer = LineGap.goToLine (startLine, buffer)
 
       val remainingWindowHeight = newWindowHeight - (TextConstants.ySpace * 2)

fcore/text-scroll.sml

@@ -37,7 +37,7 @@ struct
   fun getScrollColumnFromString (cursorIdx, windowWidth, prevScrollColumn) =
     calculateScrollColumn (0, cursorIdx, windowWidth, prevScrollColumn)
 
-  fun getStartLine (prevLineNumber, cursorLine, windowHeight) =
+  fun getStartLine (prevLineNumber, cursorLine, windowHeight, totalLines) =
     if cursorLine <= (prevLineNumber + 3) then
       (* cursorLine is prior to or same as prevLineNumber,
        * so use cursorLine to calculate the start line we want. *)
@@ -50,7 +50,10 @@ struct
         if cursorLine > prevLineNumber + (howManyLinesWeCanFit - 3) then
           (* cursorLine is after the visible part of the screen
            * so return the mimimum line where cursorLine is visible *)
-          cursorLine - howManyLinesWeCanFit + 3
+          if cursorLine >= totalLines - 3 then
+            Int.max (totalLines - howManyLinesWeCanFit, 0)
+          else
+            cursorLine - howManyLinesWeCanFit + 3
         else
           prevLineNumber
       end