From 2e01842c103c06278ab04a4f766621de17919b55 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emmanuel=20Beno=C3=AEt?= <tseeker@nocternity.net>
Date: Wed, 22 Nov 2017 10:42:28 +0100
Subject: [PATCH] Undo manager - Improved interface

* Adding returns reference to the action
* Checks for whether undo or redo are possible
---
 undo.cc |  8 +++++---
 undo.hh | 14 ++++++++++----
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/undo.cc b/undo.cc
index ef27429..db449f9 100644
--- a/undo.cc
+++ b/undo.cc
@@ -26,7 +26,7 @@ void T_UndoManager::redo( ) noexcept
 	}
 }
 
-void T_UndoManager::addAction(
+A_UndoAction& T_UndoManager::addAction(
 		P_UndoAction action ) noexcept
 {
 	assert( action );
@@ -34,12 +34,14 @@ void T_UndoManager::addAction(
 		count_ --;
 		actions_[ ( start_ + count_ ) % MaxUndo ].clear( );
 	}
+
+	const auto ai{ count_ == MaxUndo ? start_ : ( ( start_ + pos_ ) % MaxUndo ) };
 	if ( count_ == MaxUndo ) {
-		actions_[ start_ ] = std::move( action );
 		start_ = ( start_ + 1 ) % MaxUndo;
 	} else {
-		actions_[ ( start_ + pos_ ) % MaxUndo ] = std::move( action );
 		count_ ++;
 		pos_ ++;
 	}
+	actions_[ ai ] = std::move( action );
+	return *actions_[ ai ];
 }
diff --git a/undo.hh b/undo.hh
index 0180b45..c0462ae 100644
--- a/undo.hh
+++ b/undo.hh
@@ -36,22 +36,28 @@ class T_UndoManager
 	// Redo last undone action
 	void redo( ) noexcept;
 
+	// Check if it is possible to undo or redo
+	bool canUndo( ) const noexcept
+		{ return pos_ > 0; }
+	bool canRedo( ) const noexcept
+		{ return pos_ < count_; }
+
 	// Add an action using a pointer
-	void addAction( P_UndoAction action ) noexcept;
+	A_UndoAction& addAction( P_UndoAction action ) noexcept;
 
 	// Construct and add an action
 	template<
 		typename T ,
 		typename... Args
-	> void add( Args&&... args ) noexcept;
+	> A_UndoAction& add( Args&&... args ) noexcept;
 };
 
 
 template<
 	typename T ,
 	typename... Args
-> inline void T_UndoManager::add(
+> inline A_UndoAction& T_UndoManager::add(
 		Args&&... args ) noexcept
 {
-	addAction( NewOwned< T >( std::forward< Args >( args ) ... ) );
+	return addAction( NewOwned< T >( std::forward< Args >( args ) ... ) );
 }