From 91dac4aa39452fd648887056c9184d3be374ff20 Mon Sep 17 00:00:00 2001
From: Philip Withnall <philip@tecnocode.co.uk>
Date: Thu, 22 Aug 2013 21:11:49 +0000
Subject: Add [read|write]_file() support

The activity now has full support for saving games in progress.
---
diff --git a/PascalTriangle.activity/pascaltriangle.py b/PascalTriangle.activity/pascaltriangle.py
index 083693d..95d422d 100644
--- a/PascalTriangle.activity/pascaltriangle.py
+++ b/PascalTriangle.activity/pascaltriangle.py
@@ -27,6 +27,8 @@ import random
 from gi.repository import Gtk, Gdk
 import cairo
 from gettext import gettext as _
+import pickle
+import logging
 
 
 class PascalTriangleActivity(activity.Activity):
@@ -44,6 +46,9 @@ class PascalTriangleActivity(activity.Activity):
 
         self.max_participants = 1  # No sharing
 
+        # Set up logging first.
+        self._logger = logging.getLogger('pascal-triangle-activity')
+
         # Create the standard activity toolbox.
         toolbar_box = ToolbarBox()
         self.set_toolbar_box(toolbar_box)
@@ -62,6 +67,7 @@ class PascalTriangleActivity(activity.Activity):
         hint_button = HintButton(self)
         hint_button.show()
         main_toolbar.insert(hint_button, -1)
+        self._hint_button = hint_button
 
         separator = Gtk.SeparatorToolItem()
         separator.props.draw = True
@@ -114,6 +120,7 @@ class PascalTriangleActivity(activity.Activity):
 
         self._triangle_size = int(slider.get_value())
         slider.connect('value-changed', self.__slider_value_changed_cb, None)
+        self._slider = slider
 
         # Parent and show the drawing area.
         self.set_canvas(overlay)
@@ -153,6 +160,70 @@ class PascalTriangleActivity(activity.Activity):
 
         self._drawing_area.queue_draw()
 
+    def read_file(self, file_path):
+        """Read a saved game from the journal.
+
+        If this fails, the current game state will be left untouched. If extra
+        state over what was expected is present in the save file, it will be
+        ignored. For documentation on the save format, see write_file().
+        """
+        obj = None
+        try:
+            with open(file_path, 'rb') as file_fd:
+                obj = pickle.load(file_fd)
+                if len(obj) < 5:
+                    raise pickle.UnpicklingError, 'Invalid tuple.'
+        except EnvironmentError as err:
+            self._logger.warning('Error reading save file ‘%s’: %s' %
+                                 (file_path, err))
+            return
+        except pickle.UnpicklingError as err:
+            self._logger.warning('Malformed save file ‘%s’: %s' %
+                                 (file_path, err))
+            return
+
+        # Restore the UI state. Setting the triangle size will start a new
+        # game, so we must restore other state afterwards. From this point
+        # onwards, the code can't fail.
+        triangle_size = obj[0]
+        self._slider.set_value(triangle_size)
+
+        show_hints = obj[4]
+        self._hint_button.set_active(show_hints)
+
+        # Access the obj elements by index so that we don't fail if obj has
+        # more than the expected number of elements (e.g. if we've somehow
+        # got a save file from a newer version of the activity which saves
+        # more state).
+        self._blank_cells = obj[1]
+        self._current_cell = obj[2]
+        self._current_cell_text = obj[3]
+
+        # Redraw everything.
+        self._drawing_area.queue_draw()
+
+    def write_file(self, file_path):
+        """Write a game to the journal.
+
+        The game state is pickled as a tuple of at least 5 elements. This
+        format may be extended in future by appending elements to the tuple;
+        read_file() is guaranteed to ignore extra tuple elements. The existing
+        tuple elements must be stable, though.
+        """
+        obj = (
+            self._triangle_size,
+            self._blank_cells,
+            self._current_cell,
+            self._current_cell_text,
+            self._show_hints,
+        )
+
+        try:
+            with open(file_path, 'wb') as file_fd:
+                pickle.dump(obj, file_fd, pickle.HIGHEST_PROTOCOL)
+        except EnvironmentError as err:
+            self._logger.warning('Error saving game: %s' % err)
+
     def _update_current_cell(self, index):
         """Change position of the currently selected cell and clear any pending
            text edits."""
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