add functionality to go to specific line in buffer

fcore/app-update.sml

@@ -84,6 +84,30 @@ struct
       (newApp, drawMsg)
     end
 
+  fun moveToLine (app: app_type, reqLine) =
+    let
+      val {windowWidth, windowHeight, buffer, startLine = origLine, ...} = app
+      val buffer = LineGap.goToLine (reqLine, buffer)
+
+      (* get idx of first chr after linebreak *)
+      val cursorIdx = Cursor.getLineStartIdx (buffer, reqLine)
+
+      val buffer = LineGap.goToIdx (cursorIdx, buffer)
+      val startLine = TextWindow.getStartLineWithCursorCentered 
+        (buffer, cursorIdx, origLine, windowWidth, windowHeight div 2)
+
+      val buffer = LineGap.goToLine (startLine, buffer)
+
+      val newApp = AppWith.bufferAndCursorIdx
+        (app, buffer, cursorIdx, NORMAL_MODE "", startLine)
+
+      val drawMsg = 
+        TextBuilder.build
+          (startLine, cursorIdx, buffer, windowWidth, windowHeight)
+    in
+      (newApp, drawMsg)
+    end
+
   fun helpMove (app: app_type, buffer, cursorIdx, count, fMove) =
     if count = 0 then
       let
@@ -258,7 +282,10 @@ struct
         (* if str has a size larger than 0,
          * interpret as "go to line" command;
          * else, interpret as a command to move to end *)
+         if String.size str = 0 then
            moveToEnd app
+         else
+           moveToLine (app, count)
     | #"%" => moveToMatchingPair app
     (* multi-char commands which can be appended *)
     | #"t" => appendChr (app, chr, str)

fcore/cursor.sml

@@ -1703,4 +1703,43 @@ struct
           end
       | [] => cursorIdx
     end
+
+  (* Prerequisite: move lineGap to reqLine *)
+  fun getLineStartIdx (lineGap: LineGap.t, reqLine) =
+    let
+      val {rightLines, line = bufferLine, idx = bufferIdx, ...} = lineGap
+    in
+      case rightLines of
+        hd :: tl =>
+          (* reqLine exists in lineGap, so retrieve it *)
+          let
+            val relativeLine = reqLine - bufferLine - 1
+            val lineIdx = Vector.sub (hd, relativeLine)
+          in
+            bufferIdx + lineIdx + 1
+          end
+      | [] =>
+          (* reqLine does not exist in lineGap, so just go to start of last line *)
+          let
+            val {leftStrings, rightStrings, leftLines, ...} = lineGap
+          in
+            (case rightStrings of
+              hd :: _ =>
+                helpVi0 
+                  (~1, hd, bufferIdx - 1, leftStrings, leftLines)
+            | [] =>
+                (case (leftStrings, leftLines) of
+                  (lshd :: lstl, llhd :: lltl) =>
+                    let
+                      val result = helpVi0 
+                        (String.size lshd - 1, lshd, bufferIdx - 1, lstl, lltl)
+                    in
+                      if result = bufferIdx then
+                        bufferIdx - 1
+                      else
+                        result
+                    end
+                | (_, _) => 0))
+          end
+    end
 end