# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1512945681 -3600
# Node ID 337a05845a69789c02903fdb16a60da1261f3c80
# Parent  78a913d3bdef1f05822a8db084e3fac22807ea69
Ensure that periods in the managed state are copied and can therefore be edited
independently from the original values.

diff -r 78a913d3bdef -r 337a05845a69 imiptools/editing.py
--- a/imiptools/editing.py	Sat Dec 09 22:35:53 2017 +0100
+++ b/imiptools/editing.py	Sun Dec 10 23:41:21 2017 +0100
@@ -33,6 +33,16 @@
 
 # General editing abstractions.
 
+class CopiableList(list):
+
+    "A list whose elements promise to implement a copy method."
+
+    def copy(self):
+        copied = []
+        for i in self:
+            copied.append(i.copy())
+        return copied
+
 class State:
 
     "Manage editing state."
@@ -64,7 +74,12 @@
         "Return the original state for the given 'key'."
 
         self.ensure_original(key)
-        return copy(self.original[key])
+        data = self.original[key]
+        if isinstance(data, CopiableList):
+            copied = data.copy()
+        else:
+            copied = copy(self.original[key])
+        return copied
 
     def get(self, key, reset=False):
 
@@ -88,6 +103,13 @@
         self.ensure_original(key)
         self.state[key] = value
 
+    def unset(self, key):
+
+        "Unset 'key' in the state."
+
+        del self.state[key]
+        del self.original[key]
+
     def has_changed(self, key):
 
         "Return whether 'key' has changed during editing."
@@ -96,6 +118,9 @@
 
     # Dictionary emulation methods.
 
+    def __delitem__(self, key):
+        self.unset(key)
+
     def __getitem__(self, key):
         return self.get(key)
 
@@ -127,7 +152,7 @@
         self.state = State({
             "attendees"           : lambda: OrderedDict(self.obj.get_items("ATTENDEE") or []),
             "organiser"           : lambda: self.obj.get_value("ORGANIZER"),
-            "periods"             : lambda: form_periods_from_periods(self.get_unedited_periods()),
+            "periods"             : lambda: CopiableList(form_periods_from_periods(self.get_unedited_periods())),
             "suggested_attendees" : self.get_suggested_attendees,
             "suggested_periods"   : self.get_suggested_periods,
             "summary"             : lambda: self.obj.get_value("SUMMARY"),
@@ -398,7 +423,7 @@
 
         "Combine unedited and checked edited periods to make updated periods."
 
-        original = self.get_unedited_periods()
+        original = self.state.get_original("periods")
         current = self.get_checked_periods()
         return combine_periods(original, current)