1 files changed, 92 insertions, 0 deletions
diff --git a/grc/gui/StateCache.py b/grc/gui/StateCache.py
new file mode 100644
index 000000000..04b18b18a
--- /dev/null
+++ b/grc/gui/StateCache.py
@@ -0,0 +1,92 @@
+"""
+Copyright 2007 Free Software Foundation, Inc.
+This file is part of GNU Radio
+
+GNU Radio Companion 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 2
+of the License, or (at your option) any later version.
+
+GNU Radio Companion 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, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+"""
+
+from Actions import FLOW_GRAPH_UNDO, FLOW_GRAPH_REDO, get_action_from_name
+from Constants import STATE_CACHE_SIZE
+
+class StateCache(object):
+	"""
+	The state cache is an interface to a list to record data/states and to revert to previous states.
+	States are recorded into the list in a circular fassion by using an index for the current state,
+	and counters for the range where states are stored.
+	"""
+
+	def __init__(self, initial_state):
+		"""
+		StateCache constructor.
+		@param initial_state the intial state (nested data)
+		"""
+		self.states = [None] * STATE_CACHE_SIZE #fill states
+		self.current_state_index = 0
+		self.num_prev_states = 0
+		self.num_next_states = 0
+		self.states[0] = initial_state
+		self.update_actions()
+
+	def save_new_state(self, state):
+		"""
+		Save a new state.
+		Place the new state at the next index and add one to the number of previous states.
+		@param state the new state
+		"""
+		self.current_state_index = (self.current_state_index + 1)%STATE_CACHE_SIZE
+		self.states[self.current_state_index] = state
+		self.num_prev_states = self.num_prev_states + 1
+		if self.num_prev_states == STATE_CACHE_SIZE: self.num_prev_states = STATE_CACHE_SIZE - 1
+		self.num_next_states = 0
+		self.update_actions()
+
+	def get_current_state(self):
+		"""
+		Get the state at the current index.
+		@return the current state (nested data)
+		"""
+		self.update_actions()
+		return self.states[self.current_state_index]
+
+	def get_prev_state(self):
+		"""
+		Get the previous state and decrement the current index.
+		@return the previous state or None
+		"""
+		if self.num_prev_states > 0:
+			self.current_state_index = (self.current_state_index + STATE_CACHE_SIZE -1)%STATE_CACHE_SIZE
+			self.num_next_states = self.num_next_states + 1
+			self.num_prev_states = self.num_prev_states - 1
+			return self.get_current_state()
+		return None
+
+	def get_next_state(self):
+		"""
+		Get the nest state and increment the current index.
+		@return the next state or None
+		"""
+		if self.num_next_states > 0:
+			self.current_state_index = (self.current_state_index + 1)%STATE_CACHE_SIZE
+			self.num_next_states = self.num_next_states - 1
+			self.num_prev_states = self.num_prev_states + 1
+			return self.get_current_state()
+		return None
+
+	def update_actions(self):
+		"""
+		Update the undo and redo actions based on the number of next and prev states.
+		"""
+		get_action_from_name(FLOW_GRAPH_REDO).set_sensitive(self.num_next_states != 0)
+		get_action_from_name(FLOW_GRAPH_UNDO).set_sensitive(self.num_prev_states != 0)