"""HTTP cache managers

:organization: Logilab

:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr

"""

__docformat__ = "restructuredtext en"

from datetime import datetime

# time delta usable to convert localized time to GMT time

GMTOFFSET = - (datetime.now() - datetime.utcnow())

class NoHTTPCacheManager(object):

    """default cache manager: set no-cache cache control policy"""

    def __init__(self, view):

        self.view = view

        self.req = view.req

        self.rset = view.rset

    def set_headers(self):

        self.req.set_header('Cache-control', 'no-cache')

class MaxAgeHTTPCacheManager(NoHTTPCacheManager):

    """max-age cache manager: set max-age cache control policy, with max-age

    specified with the `cache_max_age` attribute of the view

    """

    def set_headers(self):

        self.req.set_header('Cache-control',

                            'max-age=%s' % self.view.cache_max_age)

class EtagHTTPCacheManager(NoHTTPCacheManager):

    """etag based cache manager for startup views

    * etag is generated using the view name and the user's groups

    * set policy to 'must-revalidate' and expires to the current time to force

      revalidation on each request

    """

    # GMT time required

    date_format = "%a, %d %b %Y %H:%M:%S GMT"

    def etag(self):

        return self.view.id + '/' + ','.join(sorted(self.req.user.groups))

    def max_age(self):

        # 0 to actually force revalidation

        return 0

    def last_modified(self):

        return self.view.last_modified()

    def set_headers(self):

        req = self.req

        try:

            req.set_header('Etag', '"%s"' % self.etag())

        except NoEtag:

            self.req.set_header('Cache-control', 'no-cache')

            return

        req.set_header('Cache-control',

                       'must-revalidate;max-age=%s' % self.max_age())

        mdate = self.last_modified()

        req.set_header('Last-modified', mdate.strftime(self.date_format))

class EntityHTTPCacheManager(EtagHTTPCacheManager):

    """etag based cache manager for view displaying a single entity

    * etag is generated using entity's eid, the view name and the user's groups

    * get last modified time from the entity definition (this may not be the

      entity's modification time since a view may include some related entities

      with a modification time to consider) using the `last_modified` method

    """

    def etag(self):

        if self.rset is None or len(self.rset) == 0: # entity startup view for instance

            return super(EntityHTTPCacheManager, self).etag()

        if len(self.rset) > 1:

            raise NoEtag()

        etag = super(EntityHTTPCacheManager, self).etag()

        eid = self.rset[0][0]

        if self.req.user.owns(eid):

            etag += ',owners'

        return str(eid) + '/' + etag

class NoEtag(Exception):

    """an etag can't be generated"""

__all__ = ('GMTOFFSET',

           'NoHTTPCacheManager', 'MaxAgeHTTPCacheManager',

           'EtagHTTPCacheManager', 'EntityHTTPCacheManager')

# monkey patching, so view doesn't depends on this module and we have all

# http cache related logic here

from cubicweb import view as viewmod

def set_http_cache_headers(self):

    self.http_cache_manager(self).set_headers()

viewmod.View.set_http_cache_headers = set_http_cache_headers

def last_modified(self):

    """return the date/time where this view should be considered as

    modified. Take care of possible related objects modifications.

    /!\ must return GMT time /!\

    """

    # XXX check view module's file modification time in dev mod ?

    ctime = datetime.utcnow()

    if self.cache_max_age:

        mtime = self.req.header_if_modified_since()

        if mtime:

            tdelta = (ctime - mtime)

            if tdelta.days * 24*60*60 + tdelta.seconds > self.cache_max_age:

                mtime = ctime

        else:

            mtime = ctime

    else:

        mtime = ctime

    # mtime = ctime will force page rerendering

    return mtime

viewmod.View.last_modified = last_modified

# configure default caching

viewmod.View.http_cache_manager = NoHTTPCacheManager

# max-age=0 to actually force revalidation when needed

viewmod.View.cache_max_age = 0

viewmod.EntityView.http_cache_manager = EntityHTTPCacheManager

viewmod.StartupView.http_cache_manager = MaxAgeHTTPCacheManager

viewmod.StartupView.cache_max_age = 60*60*2 # stay in http cache for 2 hours by default