# Copyright (C) 2015-2020 RhodeCode GmbH
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License, version 3
# (only), as published by the Free Software Foundation.
#
# This program 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 Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# This program is dual-licensed. If you wish to learn more about the
# RhodeCode Enterprise Edition, including its added features, Support services,
# and proprietary license terms, please see https://rhodecode.com/licenses/
import os
import time
import logging
import functools
import decorator
import threading

from dogpile.cache import CacheRegion

import rhodecode
from rhodecode.lib.hash_utils import sha1
from rhodecode.lib.type_utils import str2bool
from rhodecode.lib.str_utils import safe_bytes

from rhodecode.lib.rc_cache import cache_key_meta
from rhodecode.lib.rc_cache import region_meta

log = logging.getLogger(__name__)


def isCython(func):
    """
    Private helper that checks if a function is a cython function.
    """
    return func.__class__.__name__ == 'cython_function_or_method'


class RhodeCodeCacheRegion(CacheRegion):

    def conditional_cache_on_arguments(
            self, namespace=None,
            expiration_time=None,
            should_cache_fn=None,
            to_str=str,
            function_key_generator=None,
            condition=True):
        """
        Custom conditional decorator, that will not touch any dogpile internals if
        condition isn't meet. This works a bit different than should_cache_fn
        And it's faster in cases we don't ever want to compute cached values
        """
        expiration_time_is_callable = callable(expiration_time)

        if function_key_generator is None:
            function_key_generator = self.function_key_generator

        def get_or_create_for_user_func(key_generator, user_func, *arg, **kw):

            if not condition:
                log.debug('Calling un-cached method:%s', user_func.__name__)
                start = time.time()
                result = user_func(*arg, **kw)
                total = time.time() - start
                log.debug('un-cached method:%s took %.4fs', user_func.__name__, total)
                return result

            key = key_generator(*arg, **kw)

            timeout = expiration_time() if expiration_time_is_callable \
                else expiration_time

            log.debug('Calling cached method:`%s`', user_func.__name__)
            return self.get_or_create(key, user_func, timeout, should_cache_fn, (arg, kw))

        def cache_decorator(user_func):
            if to_str is str:
                # backwards compatible
                key_generator = function_key_generator(namespace, user_func)
            else:
                key_generator = function_key_generator(namespace, user_func, to_str=to_str)

            def refresh(*arg, **kw):
                """
                Like invalidate, but regenerates the value instead
                """
                key = key_generator(*arg, **kw)
                value = user_func(*arg, **kw)
                self.set(key, value)
                return value

            def invalidate(*arg, **kw):
                key = key_generator(*arg, **kw)
                self.delete(key)

            def set_(value, *arg, **kw):
                key = key_generator(*arg, **kw)
                self.set(key, value)

            def get(*arg, **kw):
                key = key_generator(*arg, **kw)
                return self.get(key)

            user_func.set = set_
            user_func.invalidate = invalidate
            user_func.get = get
            user_func.refresh = refresh
            user_func.key_generator = key_generator
            user_func.original = user_func

            # Use `decorate` to preserve the signature of :param:`user_func`.
            return decorator.decorate(user_func, functools.partial(
                get_or_create_for_user_func, key_generator))

        return cache_decorator


def make_region(*arg, **kw):
    return RhodeCodeCacheRegion(*arg, **kw)


def get_default_cache_settings(settings, prefixes=None):
    prefixes = prefixes or []
    cache_settings = {}
    for key in settings.keys():
        for prefix in prefixes:
            if key.startswith(prefix):
                name = key.split(prefix)[1].strip()
                val = settings[key]
                if isinstance(val, str):
                    val = val.strip()
                cache_settings[name] = val
    return cache_settings


def compute_key_from_params(*args):
    """
    Helper to compute key from given params to be used in cache manager
    """
    return sha1(safe_bytes("_".join(map(str, args))))


def backend_key_generator(backend):
    """
    Special wrapper that also sends over the backend to the key generator
    """
    def wrapper(namespace, fn):
        return key_generator(backend, namespace, fn)
    return wrapper


def key_generator(backend, namespace, fn):
    fname = fn.__name__

    def generate_key(*args):
        backend_prefix = getattr(backend, 'key_prefix', None) or 'backend_prefix'
        namespace_pref = namespace or 'default_namespace'
        arg_key = compute_key_from_params(*args)
        final_key = "{}:{}:{}_{}".format(backend_prefix, namespace_pref, fname, arg_key)

        return final_key

    return generate_key


def get_or_create_region(region_name, region_namespace=None):
    from rhodecode.lib.rc_cache.backends import FileNamespaceBackend
    region_obj = region_meta.dogpile_cache_regions.get(region_name)
    if not region_obj:
        raise EnvironmentError(
            'Region `{}` not in configured: {}.'.format(
                region_name, list(region_meta.dogpile_cache_regions.keys())))

    region_uid_name = '{}:{}'.format(region_name, region_namespace)
    if isinstance(region_obj.actual_backend, FileNamespaceBackend):
        region_exist = region_meta.dogpile_cache_regions.get(region_namespace)
        if region_exist:
            log.debug('Using already configured region: %s', region_namespace)
            return region_exist
        cache_dir = region_meta.dogpile_config_defaults['cache_dir']
        expiration_time = region_obj.expiration_time

        if not os.path.isdir(cache_dir):
            os.makedirs(cache_dir)
        new_region = make_region(
            name=region_uid_name,
            function_key_generator=backend_key_generator(region_obj.actual_backend)
        )
        namespace_filename = os.path.join(
            cache_dir, "{}.cache.dbm".format(region_namespace))
        # special type that allows 1db per namespace
        new_region.configure(
            backend='dogpile.cache.rc.file_namespace',
            expiration_time=expiration_time,
            arguments={"filename": namespace_filename}
        )

        # create and save in region caches
        log.debug('configuring new region: %s', region_uid_name)
        region_obj = region_meta.dogpile_cache_regions[region_namespace] = new_region

    return region_obj


def clear_cache_namespace(cache_region, cache_namespace_uid, invalidate=False):
    region = get_or_create_region(cache_region, cache_namespace_uid)
    cache_keys = region.backend.list_keys(prefix=cache_namespace_uid)
    num_delete_keys = len(cache_keys)
    if invalidate:
        region.invalidate(hard=False)
    else:
        if num_delete_keys:
            region.delete_multi(cache_keys)
    return num_delete_keys


class ActiveRegionCache(object):
    def __init__(self, context, cache_data):
        self.context = context
        self.cache_data = cache_data

    def should_invalidate(self):
        return False


class FreshRegionCache(object):
    def __init__(self, context, cache_data):
        self.context = context
        self.cache_data = cache_data

    def should_invalidate(self):
        return True


class InvalidationContext(object):
    """
    usage::

        from rhodecode.lib import rc_cache

        cache_namespace_uid = CacheKey.SOME_NAMESPACE.format(1)
        region = rc_cache.get_or_create_region('cache_perms', cache_namespace_uid)

        @region.conditional_cache_on_arguments(namespace=cache_namespace_uid, condition=True)
        def heavy_compute(cache_name, param1, param2):
            print('COMPUTE {}, {}, {}'.format(cache_name, param1, param2))

        # invalidation namespace is shared namespace key for all process caches
        # we use it to send a global signal
        invalidation_namespace = 'repo_cache:1'

        inv_context_manager = rc_cache.InvalidationContext(
            uid=cache_namespace_uid, invalidation_namespace=invalidation_namespace)
        with inv_context_manager as invalidation_context:
            args = ('one', 'two')
            # re-compute and store cache if we get invalidate signal
            if invalidation_context.should_invalidate():
                result = heavy_compute.refresh(*args)
            else:
                result = heavy_compute(*args)

            compute_time = inv_context_manager.compute_time
            log.debug('result computed in %.4fs', compute_time)

        # To send global invalidation signal, simply run
        CacheKey.set_invalidate(invalidation_namespace)

    """

    def __repr__(self):
        return f'<InvalidationContext:{self.cache_key}[{self.uid}]>'

    def __init__(self, uid, invalidation_namespace='',
                 raise_exception=False, thread_scoped=None):
        self.uid = uid
        self.invalidation_namespace = invalidation_namespace
        self.raise_exception = raise_exception
        self.proc_id = rhodecode.CONFIG.get('instance_id') or 'DEFAULT'
        self.thread_id = 'global'

        if thread_scoped is None:
            # if we set "default" we can override this via .ini settings
            thread_scoped = str2bool(rhodecode.CONFIG.get('cache_thread_scoped'))

        # Append the thread id to the cache key if this invalidation context
        # should be scoped to the current thread.
        if thread_scoped is True:
            self.thread_id = threading.current_thread().ident

        self.cache_key = compute_key_from_params(uid)
        self.cache_key = 'proc:{}|thread:{}|params:{}'.format(
            self.proc_id, self.thread_id, self.cache_key)
        self.proc_key = 'proc:{}'.format(self.proc_id)
        self.compute_time = 0

    def get_or_create_cache_obj(self, cache_type, invalidation_namespace=''):
        from rhodecode.model.db import CacheKey

        invalidation_namespace = invalidation_namespace or self.invalidation_namespace
        # fetch all cache keys for this namespace and convert them to a map to find if we
        # have specific cache_key object registered. We do this because we want to have
        # all consistent cache_state_uid for newly registered objects
        cache_obj_map = CacheKey.get_namespace_map(invalidation_namespace)
        cache_obj = cache_obj_map.get(self.cache_key)
        log.debug('Fetched cache obj %s using %s cache key.', cache_obj, self.cache_key)

        if not cache_obj:
            new_cache_args = invalidation_namespace
            first_cache_obj = next(iter(cache_obj_map.values())) if cache_obj_map else None
            cache_state_uid = None
            if first_cache_obj:
                cache_state_uid = first_cache_obj.cache_state_uid
            cache_obj = CacheKey(self.cache_key, cache_args=new_cache_args,
                                 cache_state_uid=cache_state_uid)
            cache_key_meta.cache_keys_by_pid.add(self.proc_key)

        return cache_obj

    def __enter__(self):
        """
        Test if current object is valid, and return CacheRegion function
        that does invalidation and calculation
        """
        log.debug('Entering cache invalidation check context: %s', self.invalidation_namespace)
        # register or get a new key based on uid
        self.cache_obj = self.get_or_create_cache_obj(cache_type=self.uid)
        cache_data = self.cache_obj.get_dict()
        self._start_time = time.time()
        if self.cache_obj.cache_active:
            # means our cache obj is existing and marked as it's
            # cache is not outdated, we return ActiveRegionCache
            self.skip_cache_active_change = True

            return ActiveRegionCache(context=self, cache_data=cache_data)

        # the key is either not existing or set to False, we return
        # the real invalidator which re-computes value. We additionally set
        # the flag to actually update the Database objects
        self.skip_cache_active_change = False
        return FreshRegionCache(context=self, cache_data=cache_data)

    def __exit__(self, exc_type, exc_val, exc_tb):
        from rhodecode.model.db import Session, IntegrityError

        # save compute time
        self.compute_time = time.time() - self._start_time

        if self.skip_cache_active_change:
            return

        try:
            self.cache_obj.cache_active = True
            Session().add(self.cache_obj)
            Session().commit()
        except IntegrityError:
            # if we catch integrity error, it means we inserted this object
            # assumption is that's really an edge race-condition case and
            # it's safe is to skip it
            Session().rollback()
        except Exception:
            log.exception('Failed to commit on cache key update')
            Session().rollback()
            if self.raise_exception:
                raise