History in context

routemaster/context.py

@@ -1,6 +1,6 @@
 """Context definition for exit condition programs."""
 import datetime
-from typing import Any, Dict, Iterable, Sequence
+from typing import Any, Dict, Iterable, Optional, Sequence
 
 import dateutil.tz
 
@@ -19,6 +19,7 @@ def __init__(
         now: datetime.datetime = None,
         feeds: Dict[str, Feed] = {},
         accessed_variables: Iterable[str] = [],
+        current_history_entry: Optional[Any] = None,
     ) -> None:
         """Create an execution context."""
         if now is None:
@@ -31,6 +32,7 @@ def __init__(
         self.now = now
         self.metadata = metadata
         self.feeds = feeds
+        self.current_history_entry = current_history_entry
 
         self._pre_warm_feeds(label, accessed_variables)
 
@@ -42,6 +44,7 @@ def lookup(self, path: Sequence[str]) -> Any:
             return {
                 'metadata': self._lookup_metadata,
                 'feeds': self._lookup_feed_data,
+                'history': self._lookup_history,
             }[location](rest)
         except (KeyError, ValueError):
             return None
@@ -53,6 +56,16 @@ def _lookup_feed_data(self, path: Sequence[str]) -> Any:
         feed_name, *rest = path
         return self.feeds[feed_name].lookup(rest)
 
+    def _lookup_history(self, path: Sequence[str]) -> Any:
+        if self.current_history_entry is None:
+            raise ValueError("Accessed uninitialised variable")
+
+        variable_name, = path
+        return {
+            'entered_state': self.current_history_entry.created,
+            'previous_state': self.current_history_entry.old_state,
+        }[variable_name]
+
     def property_handler(self, property_name, value, **kwargs):
         """Handle a property in execution."""
         if property_name == ('passed',):

routemaster/exit_conditions/tests/test_integration.py

@@ -1,5 +1,6 @@
 import datetime
 import textwrap
+from typing import Optional, NamedTuple
 
 import pytest
 import dateutil.tz
@@ -19,21 +20,51 @@
     ("not true", False, ()),
     ("3h has passed since metadata.old_time", True, ('metadata.old_time',)),
     ("not 4 >= 6", True, ()),
-    ("3h has not passed since metadata.old_time", False, ('metadata.old_time',)),
+    (
+        "3h has not passed since metadata.old_time",
+        False,
+        ('metadata.old_time',),
+    ),
     ("metadata.foo is defined", True, ('metadata.foo',)),
     ("metadata.bar is defined", False, ('metadata.bar',)),
     ("null is not defined", True, ()),
     ("(1 < 2) and (2 < metadata.foo)", True, ('metadata.foo',)),
     ("3 is not in metadata.objects", True, ('metadata.objects',)),
+    (
+        "12h has passed since history.entered_state",
+        True,
+        ('history.entered_state',),
+    ),
+    (
+        "1d12h has passed since history.entered_state",
+        False,
+        ('history.entered_state',),
+    ),
+    (
+        "history.previous_state = incorrect_state",
+        False,
+        ('history.previous_state', 'incorrect_state'),
+    ),
 ]
 
 
+class FakeHistoryEntry(NamedTuple):
+    created: datetime.datetime
+    old_state: Optional[str]
+    new_state: Optional[str]
+
+
 NOW = datetime.datetime(2017, 1, 1, 12, 0, 0, tzinfo=dateutil.tz.tzutc())
 VARIABLES = {
     'foo': 4,
     'objects': (2, 4),
     'old_time': NOW - datetime.timedelta(hours=4),
 }
+HISTORY_ENTRY = FakeHistoryEntry(
+    old_state='old_state',
+    new_state='new_state',
+    created=NOW - datetime.timedelta(hours=15),
+)
 
 
 @pytest.mark.parametrize("program, expected, variables", PROGRAMS)
@@ -43,6 +74,7 @@ def test_evaluate(program, expected, variables):
         label='label1',
         metadata=VARIABLES,
         now=NOW,
+        current_history_entry=HISTORY_ENTRY,
         accessed_variables=program.accessed_variables(),
     )
     assert program.run(context) == expected
@@ -144,6 +176,7 @@ def test_errors(source, error):
             label='label1',
             metadata=VARIABLES,
             now=NOW,
+            current_history_entry=HISTORY_ENTRY,
             accessed_variables=program.accessed_variables(),
         )
         program.run(context)

routemaster/tests/test_context.py

@@ -93,6 +93,14 @@ def test_non_existent_feed_is_none():
     assert context.lookup(['feeds', 'foo', 'bar']) is None
 
 
+def test_non_existent_history_variable_is_none():
+    context = Context(
+        label='label1',
+        accessed_variables=['history.foo'],
+    )
+    assert context.lookup(['history', 'foo']) is None
+
+
 def test_accessing_prefix_directly_does_not_error():
     context = Context(
         label='label1',