Refactor app module to promote code sharing.

Hopefully this is a good approach, we'll see.

tailbone/app.py

@@ -27,64 +27,110 @@ Application Entry Point
 from __future__ import unicode_literals
 
 import os
-
-from sqlalchemy import engine_from_config
+import logging
 
 import edbob
 from edbob.pyramid.forms.formalchemy import TemplateEngine
 
+import rattail.db
+from rattail.config import RattailConfig
+from rattail.exceptions import ConfigurationError
+from rattail.db.util import get_engines
+from rattail.db.continuum import configure_versioning
 from rattail.db.types import GPCType
 
 import formalchemy
 from pyramid.config import Configurator
 from pyramid.authentication import SessionAuthenticationPolicy
-from zope.sqlalchemy import ZopeTransactionExtension
 
-from tailbone.db import Session
+import tailbone.db
 from tailbone.auth import TailboneAuthorizationPolicy
 from tailbone.forms import GPCFieldRenderer
 
 
-def main(global_config, **settings):
-    """
-    This function returns a Pyramid WSGI application.
-    """
+log = logging.getLogger(__name__)
 
-    # Use Tailbone templates by default.
-    settings.setdefault('mako.directories', ['tailbone:templates'])
 
-    # Make two attempts when "retryable" errors happen during transactions.
-    # This is intended to gracefully handle database restarts.
+def make_rattail_config(settings):
+    """
+    Make a Rattail config object from the given settings.
+    """
+    # Initialize rattail config and embed it in the settings dict, to make it
+    # available to web requests later.
+    path = settings.get('edbob.config')
+    if not path or not os.path.exists(path):
+        raise ConfigurationError("Please set 'edbob.config' in [app:main] section of config "
+                                 "to the path of your config file.  Lame, but necessary.")
+    edbob.init('rattail', path)
+    log.info("using rattail config file: {0}".format(path))
+    rattail_config = RattailConfig(edbob.config)
+    settings['rattail_config'] = rattail_config
+
+    # Load all Rattail database engines from config, and store in settings
+    # dict.  This is necessary e.g. in the case of a host server, to have
+    # access to its subordinate store servers.
+    rattail_engines = get_engines(rattail_config)
+    settings['rattail_engines'] = rattail_engines
+
+    # Configure the database session classes.  Note that most of the time we'll
+    # be using the Tailbone Session, but occasionally (e.g. within batch
+    # processing threads) we want the Rattail Session.  The reason is that
+    # during normal request processing, the Tailbone Session is preferable as
+    # it includes Zope Transaction magic.  Within an explicitly-spawned thread
+    # however, this is *not* desirable.
+    rattail.db.Session.configure(bind=rattail_engines['default'])
+    tailbone.db.Session.configure(bind=rattail_engines['default'])
+
+    # Configure (or not) Continuum versioning.
+    configure_versioning(rattail_config)
+
+    return rattail_config
+
+
+def provide_postgresql_settings(settings):
+    """
+    Add some PostgreSQL-specific settings to the app config.  Specifically,
+    this enables retrying transactions a second time, in an attempt to
+    gracefully handle database restarts.
+    """
     settings.setdefault('tm.attempts', 2)
 
+
+def make_pyramid_config(settings):
+    """
+    Make a Pyramid config object from the given settings.
+    """
     config = Configurator(settings=settings)
 
-    # Initialize edbob, dammit.
-    edbob.init('rattail', os.path.abspath(settings['edbob.config']))
-    edbob.init_modules(['edbob.time'])
-
-    # Configure the primary database session.
-    engine = engine_from_config(settings)
-    Session.configure(bind=engine)
-    Session.configure(extension=ZopeTransactionExtension())
-
     # Configure user authentication / authorization.
     config.set_authentication_policy(SessionAuthenticationPolicy())
     config.set_authorization_policy(TailboneAuthorizationPolicy())
 
     # Bring in some Pyramid goodies.
     config.include('pyramid_beaker')
+    config.include('pyramid_mako')
     config.include('pyramid_tm')
 
-    # Bring in the rest of Tailbone.
-    config.include('tailbone')
-
     # Configure FormAlchemy.
     formalchemy.config.engine = TemplateEngine()
     formalchemy.FieldSet.default_renderers[GPCType] = GPCFieldRenderer
 
-    # Consider PostgreSQL server restart errors to be "retryable."
-    config.add_tween('edbob.pyramid.tweens.sqlerror_tween_factory',
+    return config
+
+
+def configure_postgresql(pyramid_config):
+    """
+    Add some PostgreSQL-specific tweaks to the final app config.  Specifically,
+    adds the tween necessary for graceful handling of database restarts.
+    """
+    pyramid_config.add_tween('edbob.pyramid.tweens.sqlerror_tween_factory',
                              under='pyramid_tm.tm_tween_factory')
 
-    return config.make_wsgi_app()
+
+def main(global_config, **settings):
+    """
+    This function returns a Pyramid WSGI application.
+    """
+    rattail_config = make_rattail_config(settings)
+    pyramid_config = make_pyramid_config(settings)
+    return pyramid_config.make_wsgi_app()