modify dedent functionality to support dedenting multiple lines, acting on count parameter

fcore/normal-mode/normal-mode.sml

@@ -59,7 +59,37 @@ struct
       loop (app, #cursorIdx app, #buffer app, count, time)
   end
 
-  (* todo: use count to find number of lines to dedent *)
+  local
+    fun loop (cursorIdx, buffer, count) =
+      if count = 0 then
+        buffer
+      else
+        let
+          val buffer = LineGap.goToIdx (cursorIdx, buffer)
+          val lineStart = Cursor.vi0 (buffer, cursorIdx)
+          val firstNonSpaceChr = Cursor.firstNonSpaceChr (buffer, lineStart)
+
+          (* delete from buffer *)
+          val difference = firstNonSpaceChr - lineStart
+          val deleteLength = Int.min (difference, 2)
+          val buffer =
+            if difference = 0 then
+              (* can't dedent as there is no leading space *)
+              buffer
+            else
+              LineGap.delete (lineStart, deleteLength, buffer)
+
+          (* get next line to dedent *)
+          val buffer = LineGap.goToIdx (lineStart, buffer)
+          val lineEnd = Cursor.viDlr (buffer, lineStart, 1)
+          val buffer = LineGap.goToIdx (lineEnd, buffer)
+          val nextLine = Cursor.viL (buffer, lineEnd)
+
+          val count = if lineEnd = nextLine then 0 else count - 1
+        in
+          loop (nextLine, buffer, count)
+        end
+  in
     fun dedentLine (app: app_type, count, time) =
       let
         open MailboxType
@@ -69,28 +99,38 @@ struct
 
         val lineStart = Cursor.vi0 (buffer, cursorIdx)
         val firstNonSpaceChr = Cursor.firstNonSpaceChr (buffer, lineStart)
-    in
+
-      if lineStart = firstNonSpaceChr then
-        (* can't dedent; no leading spaces *)
-        app
-      else
-        let
         (* calculate length to delete *)
         val difference = firstNonSpaceChr - lineStart
-          val deleteLength = if difference < 2 then difference else 2
+        val deleteLength = Int.min (difference, 2)
 
-          val buffer = LineGap.delete (lineStart, deleteLength, buffer)
+        (* delete once *)
-          val buffer = LineGap.goToStart buffer
+        val buffer =
-          val initialMsg = [SEARCH (buffer, searchString, time)]
+          if deleteLength = 0 then buffer
+          else LineGap.delete (lineStart, deleteLength, buffer)
 
-          (* The cursorIdx might be past the current line after we dedent.
+        (* Calculate nextLine and newCursorIdx.
+         * The cursorIdx might be past the current line after we dedent.
          * If it is, we put the cursorIdx at the last char of the line. *)
         val buffer = LineGap.goToIdx (lineStart, buffer)
         val lineEnd = Cursor.viDlr (buffer, lineStart, 1)
-          val cursorIdx = if lineEnd < cursorIdx then lineEnd else cursorIdx
+        val buffer = LineGap.goToIdx (lineEnd, buffer)
+        val nextLine = Cursor.viL (buffer, lineEnd)
+        val newCursorIdx = Int.min (lineEnd, cursorIdx)
+
+        val buffer =
+          if lineEnd = nextLine then
+            (* at end of file, so we cannot dedent anymore *)
+            buffer
+          else
+            (* dedent remaining lines specified by count *)
+            loop (nextLine, buffer, count - 1)
+
+        val buffer = LineGap.goToStart buffer
+        val initialMsg = [SEARCH (buffer, searchString, time)]
       in
         NormalDelete.finishAfterDeletingBuffer
-            (app, cursorIdx, buffer, time, initialMsg)
+          (app, newCursorIdx, buffer, time, initialMsg)
       end
   end