add canUndo to GameStateInfo and use to hide the undo menu

xwords4/android/XWords4/jni/xwjni.c

@@ -1409,6 +1409,7 @@ static const SetInfo gsi_ints[] = {
 };
 static const SetInfo gsi_bools[] = {
     ARR_MEMBER( GameStateInfo,canHint ),
+    ARR_MEMBER( GameStateInfo, canUndo ),
     ARR_MEMBER( GameStateInfo, canRedo ),
     ARR_MEMBER( GameStateInfo, inTrade ),
     ARR_MEMBER( GameStateInfo, tradeTilesSelected ),

xwords4/android/XWords4/src/org/eehouse/android/xw4/BoardActivity.java

@@ -764,10 +764,11 @@ public class BoardActivity extends XWActivity
                                   !inTrade && m_gsi.canHideRack );
             Utils.setItemVisible( menu, R.id.board_menu_trade, 
                                   m_gsi.canTrade );
+            Utils.setItemVisible( menu, R.id.board_menu_undo_last, 
+                                  m_gsi.canUndo );
         }
 
         Utils.setItemVisible( menu, R.id.board_menu_invite, 0 < m_missing );
-        Utils.setItemVisible( menu, R.id.board_menu_undo_last, !inTrade );
 
         Utils.setItemVisible( menu, R.id.board_menu_trade_cancel, inTrade );
         Utils.setItemVisible( menu, R.id.board_menu_trade_commit, 

xwords4/android/XWords4/src/org/eehouse/android/xw4/jni/JNIThread.java

@@ -105,6 +105,7 @@ public class JNIThread extends Thread {
         public int visTileCount;
         public int trayVisState;
         public boolean canHint;
+        public boolean canUndo;
         public boolean canRedo;
         public boolean inTrade;
         public boolean tradeTilesSelected;

xwords4/common/board.c

@@ -704,7 +704,8 @@ board_canShuffle( const BoardCtxt* board )
 XP_Bool
 board_canHideRack( const BoardCtxt* board )
 {
-    XP_Bool result = board->boardObscuresTray || !board->gameOver;
+    XP_Bool result = 0 <= server_getCurrentTurn( board->server )
+        && (board->boardObscuresTray || !board->gameOver);
     LOG_RETURNF( "%d", result );
     return result;
 }

xwords4/common/game.c

@@ -321,6 +321,7 @@ game_getState( const XWGame* game, GameStateInfo* gsi )
     gsi->trayVisState = board_getTrayVisState( board );
     gsi->visTileCount = board_visTileCount( board );
     gsi->canHint = !gameOver && board_canHint( board );
+    gsi->canUndo = model_canUndo( game->model );
     gsi->canRedo = board_canTogglePending( board );
     gsi->inTrade = board_inTrade( board, &gsi->tradeTilesSelected );
     gsi->canChat = !!game->comms && comms_canChat( game->comms );

xwords4/common/game.h

@@ -36,6 +36,7 @@ typedef struct _GameStateInfo {
     XP_U16 visTileCount;
     XW_TrayVisState trayVisState;
     XP_Bool canHint;
+    XP_Bool canUndo;
     XP_Bool canRedo;
     XP_Bool inTrade;
     XP_Bool tradeTilesSelected;

xwords4/common/model.c

@@ -822,6 +822,18 @@ model_rejectPreviousMove( ModelCtxt* model, PoolContext* pool, XP_U16* turn )
     *turn = entry.playerNum;
 } /* model_rejectPreviousMove */
 
+XP_Bool
+model_canUndo( const ModelCtxt* model )
+{
+    const StackCtxt* stack = model->vol.stack;
+    XP_U16 nStackEntries = stack_getNEntries( stack );
+
+    /* More than just tile assignment? */
+    XP_Bool result = nStackEntries > model->nPlayers;
+    LOG_RETURNF( "%d", result );
+    return result;
+}
+
 /* Undo a move, but only if it's the move we're expecting to undo (as
  * indicated by *moveNumP, if >= 0).
  */

xwords4/common/model.h

@@ -192,7 +192,7 @@ void model_commitRejectedPhony( ModelCtxt* model, XP_S16 player );
 void model_makeTileTrade( ModelCtxt* model, XP_S16 player,
                           const TrayTileSet* oldTiles, 
                           const TrayTileSet* newTiles );
-
+XP_Bool model_canUndo( const ModelCtxt* model );
 XP_Bool model_undoLatestMoves( ModelCtxt* model, PoolContext* pool, 
                                XP_U16 nMovesSought, XP_U16* turn, 
                                XP_S16* moveNum );