# Copyright (c) 2010 Google Inc. All rights reserved.

#

# Redistribution and use in source and binary forms, with or without

# modification, are permitted provided that the following conditions are

# met:

# 

#     * Redistributions of source code must retain the above copyright

# notice, this list of conditions and the following disclaimer.

#     * Redistributions in binary form must reproduce the above

# copyright notice, this list of conditions and the following disclaimer

# in the documentation and/or other materials provided with the

# distribution.

#     * Neither the name of Google Inc. nor the names of its

# contributors may be used to endorse or promote products derived from

# this software without specific prior written permission.

# 

# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

class PersistentPatchCollectionDelegate:

    def collection_name(self):

        raise NotImplementedError, "subclasses must implement"

    def fetch_potential_patch_ids(self):

        raise NotImplementedError, "subclasses must implement"

    def status_server(self):

        raise NotImplementedError, "subclasses must implement"

    def is_terminal_status(self, status):

        raise NotImplementedError, "subclasses must implement"

class PersistentPatchCollection:

    def __init__(self, delegate):

        self._delegate = delegate

        self._name = self._delegate.collection_name()

        self._status = self._delegate.status_server()

        self._status_cache = {}

    def _cached_status(self, patch_id):

        cached = self._status_cache.get(patch_id)

        if cached:

            return cached

        status = self._status.patch_status(self._name, patch_id)

        if status and self._delegate.is_terminal_status(status):

            self._status_cache[patch_id] = status

        return status

    def _is_active_patch_id(self, patch_id):

        """Active patches are patches waiting to be processed from this collection."""

        status = self._cached_status(patch_id)

        return not status or not self._delegate.is_terminal_status(status)

    def _fetch_active_patch_ids(self):

        patch_ids = self._delegate.fetch_potential_patch_ids()

        return filter(lambda patch_id: self._is_active_patch_id(patch_id), patch_ids)

    def next(self):

        # Note: We only fetch all the ids so we can post them back to the server.

        # This will go away once we have a feeder queue and all other queues are

        # just pulling their next work item from the server.

        patch_ids = self._fetch_active_patch_ids()

        # FIXME: We're assuming self._name is a valid queue-name.

        self._status.update_work_items(self._name, patch_ids)

        if not patch_ids:

            return None

        return patch_ids[0]