# MySQL Connector/Python - MySQL driver written in Python.
# Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.

# MySQL Connector/Python is licensed under the terms of the GPLv2
# <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most
# MySQL Connectors. There are special exceptions to the terms and
# conditions of the GPLv2 as it is applied to this software, see the
# FOSS License Exception
# <http://www.mysql.com/about/legal/licensing/foss-exception.html>.
#
# This program 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.
#
# 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 General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

"""Implementing caching mechanisms for MySQL Fabric"""


from datetime import datetime, timedelta
from hashlib import sha1
import logging
import threading

from . import FabricShard

_LOGGER = logging.getLogger('myconnpy-fabric')
_CACHE_TTL = 1 * 60  # 1 minute


class CacheEntry(object):

    """Base class for MySQL Fabric cache entries"""

    def __init__(self, version=None, fabric_uuid=None, ttl=_CACHE_TTL):
        self.version = version
        self.fabric_uuid = fabric_uuid
        self.last_updated = datetime.utcnow()
        self._ttl = ttl

    @classmethod
    def hash_index(cls, part1, part2=None):
        """Create hash for indexing"""
        raise NotImplementedError

    @property
    def invalid(self):
        """Returns True if entry is not valid any longer

        This property returns True when the entry is not valid any longer.
        The entry is valid when now > (last updated + ttl), where ttl is
        in seconds.
        """
        if not self.last_updated:
            return False
        atime = self.last_updated + timedelta(seconds=self._ttl)
        return datetime.utcnow() > atime

    def reset_ttl(self):
         self.last_updated = datetime.utcnow()

    def invalidate(self):
        """Invalidates the cache entry"""
        self.last_updated = None


class CacheShardTable(CacheEntry):

    """Cache entry for a Fabric sharded table"""

    def __init__(self, shard, version=None, fabric_uuid=None):
        if not isinstance(shard, FabricShard):
            ValueError("shard argument must be a FabricShard instance")
        super(CacheShardTable, self).__init__(version=version,
                                              fabric_uuid=fabric_uuid)
        self.partitioning = {}
        self._shard = shard

        if shard.key and shard.group:
            self.add_partition(shard.key, shard.group)

    def __getattr__(self, attr):
        return getattr(self._shard, attr)

    def add_partition(self, key, group):
        """Add sharding information for a group"""
        if self.shard_type == 'RANGE':
            key = int(key)
        self.partitioning[key] = {
            'group': group,
        }
        self.reset_ttl()

    @classmethod
    def hash_index(cls, part1, part2=None):
        """Create hash for indexing"""
        return sha1(part1.encode('utf-8') + part2.encode('utf-8')).hexdigest()

    def __repr__(self):
        return "{class_}({database}.{table}.{column})".format(
            class_=self.__class__,
            database=self.database,
            table=self.table,
            column=self.column
        )


class CacheGroup(CacheEntry):
    """Cache entry for a Fabric group"""
    def __init__(self, group_name, servers):
        super(CacheGroup, self).__init__(version=None, fabric_uuid=None)
        self.group_name = group_name
        self.servers = servers

    @classmethod
    def hash_index(cls, part1, part2=None):
        """Create hash for indexing"""
        return sha1(part1.encode('utf-8')).hexdigest()

    def __repr__(self):
        return "{class_}({group})".format(
            class_=self.__class__,
            group=self.group_name,
        )

class FabricCache(object):
    """Singleton class for caching Fabric data

    Only one instance of this class can exists globally.
    """
    def __init__(self, ttl=_CACHE_TTL):
        self._ttl = ttl
        self._sharding = {}
        self._groups = {}
        self.__sharding_lock = threading.Lock()
        self.__groups_lock = threading.Lock()

    def remove_group(self, entry_hash):
        """Remove cache entry for group"""
        with self.__groups_lock:
            try:
                del self._groups[entry_hash]
            except KeyError:
                # not cached, that's OK
                pass
            else:
                _LOGGER.debug("Group removed from cache")

    def remove_shardtable(self, entry_hash):
        """Remove cache entry for shard"""
        with self.__sharding_lock:
            try:
                del self._sharding[entry_hash]
            except KeyError:
                # not cached, that's OK
                pass

    def sharding_cache_table(self, shard, version=None, fabric_uuid=None):
        """Cache information about a shard"""
        entry_hash = CacheShardTable.hash_index(shard.database, shard.table)

        with self.__sharding_lock:
            try:
                entry = self._sharding[entry_hash]
                entry.add_partition(shard.key, shard.group)
            except KeyError:
                # New cache entry
                entry = CacheShardTable(shard, version=version,
                                        fabric_uuid=fabric_uuid)
                self._sharding[entry_hash] = entry

    def cache_group(self, group_name, servers):
        """Cache information about a group"""
        entry_hash = CacheGroup.hash_index(group_name)

        with self.__groups_lock:
            try:
                entry = self._groups[entry_hash]
                entry.servers = servers
                entry.reset_ttl()
                _LOGGER.debug("Recaching group {0} with {1}".format(
                    group_name, servers))
            except KeyError:
                # New cache entry
                entry = CacheGroup(group_name, servers)
                self._groups[entry_hash] = entry
                _LOGGER.debug("Caching group {0} with {1}".format(
                    group_name, servers))

    def sharding_search(self, database, table):
        """Search cache for a shard based on database and table"""
        entry_hash = CacheShardTable.hash_index(database, table)

        entry = None
        try:
            entry = self._sharding[entry_hash]
            if entry.invalid:
                _LOGGER.debug("{entry} invalidated".format(entry))
                self.remove_shardtable(entry_hash)
                return None
        except KeyError:
            # Nothing in cache
            return None

        return entry

    def group_search(self, group_name):
        """Search cache for a group based on its name"""
        entry_hash = CacheGroup.hash_index(group_name)

        entry = None
        try:
            entry = self._groups[entry_hash]
            if entry.invalid:
                _LOGGER.debug("{entry} invalidated".format(entry))
                self.remove_group(entry_hash)
                return None
        except KeyError:
            # Nothing in cache
            return None

        return entry

    def __repr__(self):
        return "{class_}(groups={nrgroups},shards={nrshards})".format(
            class_=self.__class__,
            nrgroups=len(self._groups),
            nrshards=len(self._sharding)
        )