Alowed performing undos from other player sessions, if they exist.

src/main/java/com/sk89q/worldedit/LocalPlayer.java

@@ -631,4 +631,10 @@ public abstract class LocalPlayer {
     public int hashCode() {
         return getName().hashCode();
     }
+
+    public void checkPermission(String permission) throws WorldEditPermissionException {
+       if (!hasPermission(permission)) {
+           throw new WorldEditPermissionException();
+       }
+    }
 }

src/main/java/com/sk89q/worldedit/WorldEdit.java

@@ -173,6 +173,16 @@ public class WorldEdit {
         commands.register(ToolCommands.class);
         commands.register(UtilityCommands.class);
     }
+    
+    /*
+     * Gets the LocalSession for a player name if it exists
+     *
+     * @param player
+     * @return The session for the player, if it exists
+     */
+    public LocalSession getSession(String player) {
+        return sessions.get(player);
+    }
 
     /**
      * Gets the WorldEdit session for a player.

src/main/java/com/sk89q/worldedit/WorldEditPermissionException.java

@@ -0,0 +1,10 @@
+package com.sk89q.worldedit;
+
+/**
+ * @author zml2008
+ */
+public class WorldEditPermissionException extends WorldEditException {
+    public WorldEditPermissionException() {
+        super("You don't have permission to do this.");
+    }
+}

src/main/java/com/sk89q/worldedit/commands/HistoryCommands.java

@@ -32,10 +32,10 @@ import com.sk89q.worldedit.*;
 public class HistoryCommands {
     @Command(
         aliases = {"/undo", "undo"},
-        usage = "[times]",
+        usage = "[times] [player]",
         desc = "Undoes the last action",
         min = 0,
-        max = 1
+        max = 2
     )
     @CommandPermissions({"worldedit.history.undo"})
     public static void undo(CommandContext args, WorldEdit we,
@@ -43,9 +43,19 @@ public class HistoryCommands {
             throws WorldEditException {
         
         int times = Math.max(1, args.getInteger(0, 1));
-        
         for (int i = 0; i < times; ++i) {
-            EditSession undone = session.undo(session.getBlockBag(player));
+            EditSession undone;
+            if (args.argsLength() < 2) {
+                undone = session.undo(session.getBlockBag(player));
+            } else {
+                player.checkPermission("worldedit.history.undo.other");
+                LocalSession sess = we.getSession(args.getString(1));
+                if (sess == null){
+                    player.printError("Unable to find session for " + args.getString(1));
+                    break;
+                }
+                undone = sess.undo(session.getBlockBag(player));
+            }
             if (undone != null) {
                 player.print("Undo successful.");
                 we.flushBlockBag(player, undone);
@@ -58,10 +68,10 @@ public class HistoryCommands {
     
     @Command(
         aliases = {"/redo", "redo"},
-        usage = "[times]",
+        usage = "[times] [player]",
         desc = "Redoes the last action (from history)",
         min = 0,
-        max = 1
+        max = 2
     )
     @CommandPermissions({"worldedit.history.redo"})
     public static void redo(CommandContext args, WorldEdit we,
@@ -71,7 +81,18 @@ public class HistoryCommands {
         int times = Math.max(1, args.getInteger(0, 1));
         
         for (int i = 0; i < times; ++i) {
-            EditSession redone = session.redo(session.getBlockBag(player));
+            EditSession redone;
+            if (args.argsLength() < 2) {
+                redone = session.redo(session.getBlockBag(player));
+            } else {
+                player.checkPermission("worldedit.history.redo.other");
+                LocalSession sess = we.getSession(args.getString(1));
+                if (sess == null){
+                    player.printError("Unable to find session for " + args.getString(1));
+                    break;
+                }
+                redone = sess.redo(session.getBlockBag(player));
+            }
             if (redone != null) {
                 player.print("Redo successful.");
                 we.flushBlockBag(player, redone);