Add undo support

24 files changed, 396 insertions, 26 deletions

diff --git a/src/server/events/Connect.cpp b/src/server/events/Connect.cpp
index 8880322d..f0ba39bb 100644
--- a/src/server/events/Connect.cpp
+++ b/src/server/events/Connect.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -168,6 +168,12 @@ Connect::post_process()
 	}
 }
 
+void
+Connect::undo(Interface& target)
+{
+	target.disconnect(_tail_path, _head_path);
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/Connect.hpp b/src/server/events/Connect.hpp
index f6b6cccc..bd15d6d3 100644
--- a/src/server/events/Connect.hpp
+++ b/src/server/events/Connect.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -55,6 +55,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	const Raul::Path              _tail_path;
diff --git a/src/server/events/Copy.cpp b/src/server/events/Copy.cpp
index eed68d75..34a63e58 100644
--- a/src/server/events/Copy.cpp
+++ b/src/server/events/Copy.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -211,6 +211,12 @@ Copy::post_process()
 	}
 }
 
+void
+Copy::undo(Interface& target)
+{
+	target.del(_new_uri);
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/Copy.hpp b/src/server/events/Copy.hpp
index 2677ba53..a1726cc6 100644
--- a/src/server/events/Copy.hpp
+++ b/src/server/events/Copy.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -49,6 +49,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	bool engine_to_engine();
diff --git a/src/server/events/CreateBlock.cpp b/src/server/events/CreateBlock.cpp
index 7ba35d1a..cde15622 100644
--- a/src/server/events/CreateBlock.cpp
+++ b/src/server/events/CreateBlock.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -164,6 +164,12 @@ CreateBlock::post_process()
 	}
 }
 
+void
+CreateBlock::undo(Interface& target)
+{
+	target.del(_block->uri());
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/CreateBlock.hpp b/src/server/events/CreateBlock.hpp
index 40d72f52..1282fe8b 100644
--- a/src/server/events/CreateBlock.hpp
+++ b/src/server/events/CreateBlock.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -50,6 +50,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	Raul::Path            _path;
diff --git a/src/server/events/CreateGraph.cpp b/src/server/events/CreateGraph.cpp
index e6ad0cb4..93191437 100644
--- a/src/server/events/CreateGraph.cpp
+++ b/src/server/events/CreateGraph.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -213,6 +213,12 @@ CreateGraph::post_process()
 	_child_events.clear();
 }
 
+void
+CreateGraph::undo(Interface& target)
+{
+	target.del(_graph->uri());
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/CreateGraph.hpp b/src/server/events/CreateGraph.hpp
index cf40fb41..efeabf48 100644
--- a/src/server/events/CreateGraph.hpp
+++ b/src/server/events/CreateGraph.hpp
@@ -47,6 +47,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 	GraphImpl* graph() { return _graph; }
 
diff --git a/src/server/events/CreatePort.cpp b/src/server/events/CreatePort.cpp
index 0f711f4f..0e512852 100644
--- a/src/server/events/CreatePort.cpp
+++ b/src/server/events/CreatePort.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -197,6 +197,12 @@ CreatePort::post_process()
 	delete _old_ports_array;
 }
 
+void
+CreatePort::undo(Interface& target)
+{
+	target.del(_graph_port->uri());
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/CreatePort.hpp b/src/server/events/CreatePort.hpp
index a2dd55ce..754a238f 100644
--- a/src/server/events/CreatePort.hpp
+++ b/src/server/events/CreatePort.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -54,6 +54,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	enum class Flow {
diff --git a/src/server/events/Delete.cpp b/src/server/events/Delete.cpp
index 06a5cb95..7b27e11f 100644
--- a/src/server/events/Delete.cpp
+++ b/src/server/events/Delete.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -162,6 +162,18 @@ Delete::post_process()
 	}
 }
 
+void
+Delete::undo(Interface& target)
+{
+	auto i = _removed_objects.find(_path);
+	if (i != _removed_objects.end()) {
+		target.put(_uri, i->second->properties());
+		if (_disconnect_event) {
+			_disconnect_event->undo(target);
+		}
+	}
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/Delete.hpp b/src/server/events/Delete.hpp
index 4403d4da..c6e38839 100644
--- a/src/server/events/Delete.hpp
+++ b/src/server/events/Delete.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -57,6 +57,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	Raul::URI               _uri;
diff --git a/src/server/events/Delta.cpp b/src/server/events/Delta.cpp
index 83312814..a765932b 100644
--- a/src/server/events/Delta.cpp
+++ b/src/server/events/Delta.cpp
@@ -277,6 +277,7 @@ Delta::pre_process()
 				_old_bindings = _engine.control_bindings()->remove(port);
 		}
 		if (_object) {
+			_removed.emplace(key, value);
 			_object->remove_property(key, value);
 		} else if (is_engine && key == uris.ingen_loadedBundle) {
  			LilvWorld* lworld = _engine.world()->lilv_world();
@@ -299,8 +300,23 @@ Delta::pre_process()
 
 	// Remove all added properties if this is a put or set
 	if (_object && (_type == Type::PUT || _type == Type::SET)) {
-		for (const auto& p : _properties) {
-			_object->remove_property(p.first, uris.patch_wildcard);
+		for (auto p = _properties.begin();
+		     p != _properties.end();
+		     p = _properties.upper_bound(p->first)) {
+			for (auto q = _object->properties().find(p->first);
+			     q != _object->properties().end() && q->first == p->first;) {
+				auto next = q;
+				++next;
+
+				if (!_properties.contains(q->first, q->second)) {
+					const auto r = std::make_pair(q->first, q->second);
+					_object->properties().erase(q);
+					_object->on_property_removed(r.first, r.second);
+					_removed.insert(r);
+				}
+
+				q = next;
+			}
 		}
 	}
 
@@ -311,7 +327,9 @@ Delta::pre_process()
 		if (obj) {
 			Resource& resource = *obj;
 			if (value != uris.patch_wildcard) {
-				resource.add_property(key, value, value.context());
+				if (resource.add_property(key, value, value.context())) {
+					_added.emplace(key, value);
+				}
 			}
 
 			BlockImpl* block = NULL;
@@ -589,12 +607,16 @@ Delta::post_process()
 			/* Kludge to avoid feedback for set events only.  The GUI
 			   depends on put responses to e.g. initially place blocks.
 			   Some more sensible way of controlling this is needed. */
-			_engine.broadcaster()->set_ignore_client(_request_client);
+			if (_mode == Mode::NORMAL) {
+				_engine.broadcaster()->set_ignore_client(_request_client);
+			}
 			_engine.broadcaster()->set_property(
 				_subject,
-				(*_properties.begin()).first,
-				(*_properties.begin()).second);
-			_engine.broadcaster()->clear_ignore_client();
+				_properties.begin()->first,
+				_properties.begin()->second);
+			if (_mode == Mode::NORMAL) {
+				_engine.broadcaster()->clear_ignore_client();
+			}
 			break;
 		case Type::PUT:
 			if (_type == Type::PUT && _subject.substr(0, 5) == "file:") {
@@ -614,6 +636,27 @@ Delta::post_process()
 	}
 }
 
+void
+Delta::undo(Interface& target)
+{
+	const Ingen::URIs& uris = _engine.world()->uris();
+
+	if (_create_event) {
+		_create_event->undo(target);
+	} else if (_type == Type::PATCH) {
+		target.delta(_subject, _added, _removed);
+	} else if (_type == Type::SET || _type == Type::PUT) {
+		if (_removed.size() == 1) {
+			target.set_property(
+				_subject, _removed.begin()->first, _removed.begin()->second);
+		} else if (_removed.empty()) {
+			target.delta(_subject, _added, {});
+		} else {
+			target.put(_subject, _removed);
+		}
+	}
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/Delta.hpp b/src/server/events/Delta.hpp
index e9d1970b..b1f2d66a 100644
--- a/src/server/events/Delta.hpp
+++ b/src/server/events/Delta.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -76,6 +76,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	enum class SpecialType {
@@ -107,6 +108,9 @@ private:
 	ControlBindings::Key     _binding;
 	Type                     _type;
 
+	Resource::Properties _added;
+	Resource::Properties _removed;
+
 	SPtr<ControlBindings::Bindings> _old_bindings;
 
 	boost::optional<Resource> _preset;
diff --git a/src/server/events/Disconnect.cpp b/src/server/events/Disconnect.cpp
index 6f84dc1a..13f419ce 100644
--- a/src/server/events/Disconnect.cpp
+++ b/src/server/events/Disconnect.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -219,6 +219,12 @@ Disconnect::post_process()
 	}
 }
 
+void
+Disconnect::undo(Interface& target)
+{
+	target.connect(_tail_path, _head_path);
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/Disconnect.hpp b/src/server/events/Disconnect.hpp
index 64e08246..8a69dac4 100644
--- a/src/server/events/Disconnect.hpp
+++ b/src/server/events/Disconnect.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -57,6 +57,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 	class Impl {
 	public:
@@ -67,7 +68,8 @@ public:
 
 		bool execute(ProcessContext& context, bool set_head_buffers);
 
-		inline InputPort* head() { return _head; }
+		inline OutputPort* tail() { return _tail; }
+		inline InputPort*  head() { return _head; }
 
 	private:
 		Engine&                       _engine;
diff --git a/src/server/events/DisconnectAll.cpp b/src/server/events/DisconnectAll.cpp
index bd4fef7d..ee19797e 100644
--- a/src/server/events/DisconnectAll.cpp
+++ b/src/server/events/DisconnectAll.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -164,6 +164,14 @@ DisconnectAll::post_process()
 	}
 }
 
+void
+DisconnectAll::undo(Interface& target)
+{
+	for (auto& i : _impls) {
+		target.connect(i->tail()->path(), i->head()->path());
+	}
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/DisconnectAll.hpp b/src/server/events/DisconnectAll.hpp
index 039e3f54..f8123a45 100644
--- a/src/server/events/DisconnectAll.hpp
+++ b/src/server/events/DisconnectAll.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -59,6 +59,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	typedef std::list<Disconnect::Impl*> Impls;
diff --git a/src/server/events/Mark.cpp b/src/server/events/Mark.cpp
new file mode 100644
index 00000000..0e14f008
--- /dev/null
+++ b/src/server/events/Mark.cpp
@@ -0,0 +1,65 @@
+/*
+  This file is part of Ingen.
+  Copyright 2016 David Robillard <http://drobilla.net/>
+
+  Ingen is free software: you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free
+  Software Foundation, either version 3 of the License, or any later version.
+
+  Ingen is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with Ingen.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "Engine.hpp"
+#include "UndoStack.hpp"
+#include "events/Mark.hpp"
+
+namespace Ingen {
+namespace Server {
+namespace Events {
+
+Mark::Mark(Engine&         engine,
+           SPtr<Interface> client,
+           int32_t         id,
+           SampleCount     timestamp,
+           Type            type)
+	: Event(engine, client, id, timestamp)
+	, _type(type)
+{}
+
+bool
+Mark::pre_process()
+{
+	UndoStack* const stack = ((_mode == Mode::UNDO)
+	                          ? _engine.redo_stack()
+	                          : _engine.undo_stack());
+
+	switch (_type) {
+	case Type::BUNDLE_START:
+		stack->start_entry();
+		break;
+	case Type::BUNDLE_END:
+		stack->finish_entry();
+		break;
+	}
+
+	return Event::pre_process_done(Status::SUCCESS);
+}
+
+void
+Mark::execute(ProcessContext& context)
+{}
+
+void
+Mark::post_process()
+{
+	respond();
+}
+
+} // namespace Events
+} // namespace Server
+} // namespace Ingen
diff --git a/src/server/events/Mark.hpp b/src/server/events/Mark.hpp
new file mode 100644
index 00000000..995df746
--- /dev/null
+++ b/src/server/events/Mark.hpp
@@ -0,0 +1,55 @@
+/*
+  This file is part of Ingen.
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
+
+  Ingen is free software: you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free
+  Software Foundation, either version 3 of the License, or any later version.
+
+  Ingen is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with Ingen.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef INGEN_EVENTS_MARK_HPP
+#define INGEN_EVENTS_MARK_HPP
+
+#include "Event.hpp"
+
+namespace Ingen {
+namespace Server {
+
+class Engine;
+
+namespace Events {
+
+/** Set properties of a graph object.
+ * \ingroup engine
+ */
+class Mark : public Event
+{
+public:
+	enum class Type { BUNDLE_START, BUNDLE_END };
+
+	Mark(Engine&                     engine,
+	     SPtr<Interface>             client,
+	     int32_t                     id,
+	     SampleCount                 timestamp,
+	     Type                        type);
+
+	bool pre_process();
+	void execute(ProcessContext& context);
+	void post_process();
+
+private:
+	Type _type;
+};
+
+} // namespace Events
+} // namespace Server
+} // namespace Ingen
+
+#endif // INGEN_EVENTS_MARK_HPP
diff --git a/src/server/events/Move.cpp b/src/server/events/Move.cpp
index 2c689fe5..a51617cb 100644
--- a/src/server/events/Move.cpp
+++ b/src/server/events/Move.cpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -87,6 +87,12 @@ Move::post_process()
 	}
 }
 
+void
+Move::undo(Interface& target)
+{
+	target.move(_new_path, _old_path);
+}
+
 } // namespace Events
 } // namespace Server
 } // namespace Ingen
diff --git a/src/server/events/Move.hpp b/src/server/events/Move.hpp
index ae811138..74d32c61 100644
--- a/src/server/events/Move.hpp
+++ b/src/server/events/Move.hpp
@@ -1,6 +1,6 @@
 /*
   This file is part of Ingen.
-  Copyright 2007-2015 David Robillard <http://drobilla.net/>
+  Copyright 2007-2016 David Robillard <http://drobilla.net/>
 
   Ingen is free software: you can redistribute it and/or modify it under the
   terms of the GNU Affero General Public License as published by the Free
@@ -48,6 +48,7 @@ public:
 	bool pre_process();
 	void execute(ProcessContext& context);
 	void post_process();
+	void undo(Interface& target);
 
 private:
 	const Raul::Path _old_path;
diff --git a/src/server/events/Undo.cpp b/src/server/events/Undo.cpp
new file mode 100644
index 00000000..28b8e188
--- /dev/null
+++ b/src/server/events/Undo.cpp
@@ -0,0 +1,77 @@
+/*
+  This file is part of Ingen.
+  Copyright 2016 David Robillard <http://drobilla.net/>
+
+  Ingen is free software: you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free
+  Software Foundation, either version 3 of the License, or any later version.
+
+  Ingen is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with Ingen.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "ingen/AtomReader.hpp"
+
+#include "Engine.hpp"
+#include "EventWriter.hpp"
+#include "Undo.hpp"
+
+namespace Ingen {
+namespace Server {
+namespace Events {
+
+Undo::Undo(Engine&          engine,
+           SPtr<Interface>  client,
+           int32_t          id,
+           SampleCount      timestamp,
+           bool             is_redo)
+	: Event(engine, client, id, timestamp)
+	, _is_redo(is_redo)
+{}
+
+bool
+Undo::pre_process()
+{
+	UndoStack* stack = _is_redo ? _engine.redo_stack() : _engine.undo_stack();
+	Event::Mode mode = _is_redo ? Event::Mode::REDO    : Event::Mode::UNDO;
+
+	if (stack->empty()) {
+		return Event::pre_process_done(Status::NOT_FOUND);
+	}
+
+	_entry = stack->pop();
+	_engine.interface()->set_event_mode(mode);
+	if (_entry.events.size() > 1) {
+		_engine.interface()->bundle_begin();
+	}
+
+	for (const LV2_Atom* ev : _entry.events) {
+		_engine.atom_interface()->write(ev);
+	}
+
+	if (_entry.events.size() > 1) {
+		_engine.interface()->bundle_end();
+	}
+	_engine.interface()->set_event_mode(mode);
+
+	return Event::pre_process_done(Status::SUCCESS);
+}
+
+void
+Undo::execute(ProcessContext& context)
+{
+}
+
+void
+Undo::post_process()
+{
+	respond();
+}
+
+} // namespace Events
+} // namespace Server
+} // namespace Ingen
diff --git a/src/server/events/Undo.hpp b/src/server/events/Undo.hpp
new file mode 100644
index 00000000..fff06b8d
--- /dev/null
+++ b/src/server/events/Undo.hpp
@@ -0,0 +1,54 @@
+/*
+  This file is part of Ingen.
+  Copyright 2016 David Robillard <http://drobilla.net/>
+
+  Ingen is free software: you can redistribute it and/or modify it under the
+  terms of the GNU Affero General Public License as published by the Free
+  Software Foundation, either version 3 of the License, or any later version.
+
+  Ingen is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with Ingen.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef INGEN_EVENTS_UNDO_HPP
+#define INGEN_EVENTS_UNDO_HPP
+
+#include "Event.hpp"
+#include "UndoStack.hpp"
+#include "types.hpp"
+
+namespace Ingen {
+namespace Server {
+namespace Events {
+
+/** A request to undo the last change to the engine.
+ *
+ * \ingroup engine
+ */
+class Undo : public Event
+{
+public:
+	Undo(Engine&         engine,
+	     SPtr<Interface> client,
+	     int32_t         id,
+	     SampleCount     timestamp,
+	     bool            is_redo);
+
+	bool pre_process();
+	void execute(ProcessContext& context);
+	void post_process();
+
+private:
+	UndoStack::Entry _entry;
+	bool             _is_redo;
+};
+
+} // namespace Events
+} // namespace Server
+} // namespace Ingen
+
+#endif // INGEN_EVENTS_UNDO_HPP