Fix bag of moveCursor

ui/cursor.go

@@ -17,14 +17,20 @@ func (cursor *Cursor) FindPosition(g *gocui.Gui, viewName string) (int, int, err
 	return yOffset, yCurrent, nil
 }
 
+func (Cursor *Cursor) getMaxLineLength(v *gocui.View) int {
+	return len(v.BufferLines())
+}
+
 func (cursor *Cursor) MoveToFirst(g *gocui.Gui, v *gocui.View) error {
-	yOffset, yCurrent, err := cursor.FindPosition(g, v.Name())
-	if err != nil {
-		panic(err)
-	}
-	cursor.Move(g, v, -(yOffset + yCurrent), nil)
+	v.SetCursor(0, 0)
+	v.SetOrigin(0, 0)
 	return nil
 }
+func (cursor *Cursor) lineBelow(g *gocui.Gui, v *gocui.View, d int) bool {
+	yOffset, yCurrent, _ := cursor.FindPosition(g, v.Name())
+	_, err := v.Line(yOffset + yCurrent + d)
+	return err == nil && cursor.getMaxLineLength(v) >= yOffset+yCurrent+d && 0 <= yOffset+yCurrent+d
+}
 
 func (cursor *Cursor) Move(g *gocui.Gui, v *gocui.View, d int, callback func(int, int) error) bool {
 	dir := 1
@@ -33,13 +39,14 @@ func (cursor *Cursor) Move(g *gocui.Gui, v *gocui.View, d int, callback func(int
 	}
 	distance := int(math.Abs(float64(d)))
 	for ; distance > 0; distance-- {
-		v.MoveCursor(0, distance*dir, false)
-		yOffset, yCurrent, _ := cursor.FindPosition(g, v.Name())
-		if callback != nil {
-			callback(yOffset, yCurrent)
+		if cursor.lineBelow(g, v, distance*dir) {
+			v.MoveCursor(0, distance*dir, false)
+			yOffset, yCurrent, _ := cursor.FindPosition(g, v.Name())
+			if callback != nil {
+				callback(yOffset, yCurrent)
+			}
+			return true
 		}
-
-		return true
 	}
 	return false
 }