Add custom Exception Handlers (#43)

* Add the ability to register exception handlers to handle exceptions that occur while executing a command

* you saw nothing

* add ability to cancel default error message

* per command exception handler

* add a getter for the default exception handler

core/src/main/java/co/aikar/commands/BaseCommand.java

@@ -76,6 +76,8 @@ public abstract class BaseCommand {
     String permission;
     public String permissionMessage = "&cI'm sorry, but you do not have permission to perform this command.";
 
+    private ExceptionHandler exceptionHandler = null;
+
     public BaseCommand() {}
     public BaseCommand(String cmd) {
         this.commandName = cmd;
@@ -512,6 +514,15 @@ public abstract class BaseCommand {
         return commandName;
     }
 
+    public ExceptionHandler getExceptionHandler() {
+        return exceptionHandler;
+    }
+
+    public BaseCommand setExceptionHandler(ExceptionHandler exceptionHandler) {
+        this.exceptionHandler = exceptionHandler;
+        return this;
+    }
+
     private static class CommandSearch { RegisteredCommand cmd; int argIndex; String checkSub;
 
         CommandSearch(RegisteredCommand cmd, int argIndex, String checkSub) {

core/src/main/java/co/aikar/commands/CommandManager.java

@@ -34,6 +34,7 @@ abstract class CommandManager {
 
     protected Map<String, RootCommand> rootCommands = new HashMap<>();
     protected CommandReplacements replacements = new CommandReplacements(this);
+    protected ExceptionHandler defaultExceptionHandler = null;
 
     /**
      * Gets the command contexts manager
@@ -92,4 +93,32 @@ abstract class CommandManager {
     public abstract void log(final LogLevel level, final String message);
 
     public abstract void log(final LogLevel level, final String message, final Throwable throwable);
+
+    /**
+     * Sets the default {@link ExceptionHandler} that is called when an exception occurs while executing a command, if the command doesn't have it's own exception handler registered.
+     *
+     * @param exceptionHandler the handler that should handle uncaught exceptions
+     */
+    public void setDefaultExceptionHandler(ExceptionHandler exceptionHandler){
+        defaultExceptionHandler = exceptionHandler;
+    }
+
+    /**
+     * Gets the current default exception handler, might be null.
+     *
+     * @return the default exception handler
+     */
+    public ExceptionHandler getDefaultExceptionHandler() {
+        return defaultExceptionHandler;
+    }
+
+    protected boolean handleUncaughtException(BaseCommand scope, RegisteredCommand registeredCommand, CommandIssuer sender, List<String> args, Throwable t){
+        boolean result = false;
+        if(scope.getExceptionHandler() != null){
+            result = scope.getExceptionHandler().execute(scope, registeredCommand, sender, args, t);
+        }else if(defaultExceptionHandler != null){
+            result = defaultExceptionHandler.execute(scope, registeredCommand, sender, args, t);
+        }
+        return result;
+    }
 }

core/src/main/java/co/aikar/commands/ExceptionHandler.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2016-2017 Daniel Ennis (Aikar) - MIT License
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining
+ *  a copy of this software and associated documentation files (the
+ *  "Software"), to deal in the Software without restriction, including
+ *  without limitation the rights to use, copy, modify, merge, publish,
+ *  distribute, sublicense, and/or sell copies of the Software, and to
+ *  permit persons to whom the Software is furnished to do so, subject to
+ *  the following conditions:
+ *
+ *  The above copyright notice and this permission notice shall be
+ *  included in all copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package co.aikar.commands;
+
+import java.util.List;
+
+/**
+ * Functional interface to allow plugins to handle uncaught excetpions
+ */
+@FunctionalInterface
+public interface ExceptionHandler {
+
+  /**
+   * Called when an exception occurs while executing a command<br>
+   * If an exception handler properly handles an exception, the user will not be noticied by the
+   * framework that something went unexceptected.
+   *
+   * @param command the command that was executed
+   * @param registeredCommand the registered command
+   * @param sender the issuer who send the command
+   * @param args the args he used
+   * @param t the throwable that caused this exception
+   *
+   * @return if the exception was handeled by the exception handler.
+   */
+  boolean execute(BaseCommand command, RegisteredCommand registeredCommand, CommandIssuer sender, List<String> args, Throwable t);
+}

core/src/main/java/co/aikar/commands/RegisteredCommand.java

@@ -153,7 +153,10 @@ public class RegisteredCommand <R extends CommandExecutionContext<? extends Comm
                 scope.showSyntax(sender, this);
             }
         } else {
-            sender.sendMessage("&cI'm sorry, but there was an error performing this command.");
+            boolean handeled = this.scope.manager.handleUncaughtException(scope, this, sender, args, e);
+            if(!handeled){
+                sender.sendMessage("&cI'm sorry, but there was an error performing this command.");
+            }
             this.scope.manager.log(LogLevel.ERROR, "Exception in command: " + command + " " + ACFUtil.join(args), e);
         }
     }

example/src/main/java/co/aikar/acfexample/ACFExample.java

@@ -45,8 +45,17 @@ public final class ACFExample extends JavaPlugin {
         commandManager.getCommandCompletions().registerCompletion("test", c -> (
             Lists.newArrayList("foo", "bar", "baz")
         ));
-        commandManager.registerCommand(new SomeCommand());
+
+        commandManager.registerCommand(new SomeCommand().setExceptionHandler((command, registeredCommand, sender, args, t) -> {
+                sender.sendMessage("An error occured. This problem has been logged. Sorry for the inconvienence.");
+                return true; // mark as handeled, default message will not be send to sender
+        }));
         commandManager.registerCommand(new SomeCommand_ExtraSubs());
+
+        commandManager.setDefaultExceptionHandler((command, registeredCommand, sender, args, t) -> {
+            getLogger().warning("Error occured while executing command " + command.getName());
+            return false; // mark as unhandeled, sender will see default message
+        });
     }
 
     public static ACFExample getPlugin() {