1 files changed, 156 insertions, 0 deletions

diff --git a/src/mailman/app/workflow.py b/src/mailman/app/workflow.py
new file mode 100644
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+++ b/src/mailman/app/workflow.py
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+# Copyright (C) 2015 by the Free Software Foundation, Inc.
+#
+# This file is part of GNU Mailman.
+#
+# GNU Mailman 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 3 of the License, or (at your option)
+# any later version.
+#
+# GNU Mailman 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
+# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Generic workflow."""
+
+__all__ = [
+    'Workflow',
+    ]
+
+
+import sys
+import json
+import logging
+
+from collections import deque
+from mailman.interfaces.workflow import IWorkflowStateManager
+from zope.component import getUtility
+
+
+COMMASPACE = ', '
+log = logging.getLogger('mailman.error')
+
+
+
+class Workflow:
+    """Generic workflow."""
+
+    SAVE_ATTRIBUTES = ()
+    INITIAL_STATE = None
+
+    def __init__(self):
+        self.token = None
+        self._next = deque()
+        self.push(self.INITIAL_STATE)
+        self.debug = False
+        self._count = 0
+
+    @property
+    def name(self):
+        return self.__class__.__name__
+
+    def __iter__(self):
+        return self
+
+    def push(self, step):
+        self._next.append(step)
+
+    def _pop(self):
+        name = self._next.popleft()
+        step = getattr(self, '_step_{}'.format(name))
+        self._count += 1
+        if self.debug:
+            print('[{:02d}] -> {}'.format(self._count, name), file=sys.stderr)
+        return name, step
+
+    def __next__(self):
+        try:
+            name, step = self._pop()
+            return step()
+        except IndexError:
+            raise StopIteration
+        except:
+            log.exception('deque: {}'.format(COMMASPACE.join(self._next)))
+            raise
+
+    def run_thru(self, stop_after):
+        """Run the state machine through and including the given step.
+
+        :param stop_after: Name of method, sans prefix to run the
+            state machine through.  In other words, the state machine runs
+            until the named method completes.
+        """
+        results = []
+        while True:
+            try:
+                name, step = self._pop()
+            except (StopIteration, IndexError):
+                # We're done.
+                break
+            results.append(step())
+            if name == stop_after:
+                break
+        return results
+
+    def run_until(self, stop_before):
+        """Trun the state machine until (not including) the given step.
+
+        :param stop_before: Name of method, sans prefix that the
+            state machine is run until the method is reached.  Unlike
+            `run_thru()` the named method is not run.
+        """
+        results = []
+        while True:
+            try:
+                name, step = self._pop()
+            except (StopIteration, IndexError):
+                # We're done.
+                break
+            if name == stop_before:
+                # Stop executing, but not before we push the last state back
+                # onto the deque.  Otherwise, resuming the state machine would
+                # skip this step.
+                self._next.appendleft(step)
+                break
+            results.append(step())
+        return results
+
+    def save(self):
+        assert self.token, 'Workflow token must be set'
+        state_manager = getUtility(IWorkflowStateManager)
+        data = {attr: getattr(self, attr) for attr in self.SAVE_ATTRIBUTES}
+        # Note: only the next step is saved, not the whole stack.  This is not
+        # an issue in practice, since there's never more than a single step in
+        # the queue anyway.  If we want to support more than a single step in
+        # the queue *and* want to support state saving/restoring, change this
+        # method and the restore() method.
+        if len(self._next) == 0:
+            step = None
+        elif len(self._next) == 1:
+            step = self._next[0]
+        else:
+            raise AssertionError(
+                "Can't save a workflow state with more than one step "
+                "in the queue")
+        state_manager.save(
+            self.__class__.__name__,
+            self.token,
+            step,
+            json.dumps(data))
+
+    def restore(self):
+        state_manager = getUtility(IWorkflowStateManager)
+        state = state_manager.restore(self.__class__.__name__, self.token)
+        if state is None:
+            # The token doesn't exist in the database.
+            raise LookupError(self.token)
+        self._next.clear()
+        if state.step:
+            self._next.append(state.step)
+        if state.data is not None:
+            for attr, value in json.loads(state.data).items():
+                setattr(self, attr, value)