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/*
* Copyright (C) 2017-2018 Olzhas Rakhimov
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/// @file
/// Undo-redo helper facilities based on the Qt Undo framework.
///
/// Undo-redo facilities assume the following contract:
///
/// 0. The facilities are special purpose to work with the undo-redo stack.
/// 1. The redo is always called first.
/// 2. The undo-redo functions are not required to be idempotent.
/// Calling the redo (or undo) consecutively yields undefined behavior.
/// In other words, the redo can only be followed by the undo,
/// and the undo can only be followed by the redo.
/// 3. The system state is only changed with the undo-redo facilities.
/// 4. As a consequence of contract #2 and #3,
/// the implementation can and should optimize the state storage
/// to hold only single snapshot data (no duplication of the state).
/// That is, the redo stage saves the past (by overwriting the future),
/// and the undo stage saves the future by overwriting the saved past.
/// 5. Objects (undo-redo arguments) must be alive and have stable addresses for
/// at least as long as there's a referencing undo-redo command in the stack.
/// Constructive/destructive commands extend
/// the life-time of an object for this reason.
/// That is, destructive commands do not destroy/deallocate at redo
/// or re-construct/allocate at undo (vice-versa for the constructive).
/// The object is destroyed/deallocated
/// after its corresponding constructive/destructive commands are destroyed
/// (e.g., by being popped/removed from the undo stack).
#pragma once
#include <type_traits>
#include <QUndoCommand>
namespace scram::gui {
/// The function inverse is the function itself (i.e., f(f(x)) = id(x)).
/// In other words, undo and redo codes are exactly the same,
/// but the arguments are different (one's output is the other's argument).
/// In this case, the argument is the state of the object or system.
class Involution : public QUndoCommand
{
public:
using QUndoCommand::QUndoCommand;
/// The redo is always called first;
/// therefore, undo is implemented in terms of redo.
void undo() final { return redo(); }
};
/// A command that is an inverse of another command.
///
/// @tparam T The undo-redo command type.
///
/// @pre T command can tolerate the undo before the redo.
template <class T>
class Inverse : public T
{
static_assert(std::is_base_of_v<QUndoCommand, T>);
public:
/// Applies the command.
void redo() final { T::undo(); }
/// Reverses the command.
void undo() final { T::redo(); }
protected:
using T::T;
};
} // namespace scram::gui
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