#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2014-2015 Canonical Limited.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#  http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Authors:
#  Kapil Thangavelu <kapil.foss@gmail.com>
#
"""
Intro
-----

A simple way to store state in units. This provides a key value
storage with support for versioned, transactional operation,
and can calculate deltas from previous values to simplify unit logic
when processing changes.


Hook Integration
----------------

There are several extant frameworks for hook execution, including

 - charmhelpers.core.hookenv.Hooks
 - charmhelpers.core.services.ServiceManager

The storage classes are framework agnostic, one simple integration is
via the HookData contextmanager. It will record the current hook
execution environment (including relation data, config data, etc.),
setup a transaction and allow easy access to the changes from
previously seen values. One consequence of the integration is the
reservation of particular keys ('rels', 'unit', 'env', 'config',
'charm_revisions') for their respective values.

Here's a fully worked integration example using hookenv.Hooks::

       from charmhelper.core import hookenv, unitdata

       hook_data = unitdata.HookData()
       db = unitdata.kv()
       hooks = hookenv.Hooks()

       @hooks.hook
       def config_changed():
           # Print all changes to configuration from previously seen
           # values.
           for changed, (prev, cur) in hook_data.conf.items():
               print('config changed', changed,
                     'previous value', prev,
                     'current value',  cur)

           # Get some unit specific bookeeping
           if not db.get('pkg_key'):
               key = urllib.urlopen('https://example.com/pkg_key').read()
               db.set('pkg_key', key)

           # Directly access all charm config as a mapping.
           conf = db.getrange('config', True)

           # Directly access all relation data as a mapping
           rels = db.getrange('rels', True)

       if __name__ == '__main__':
           with hook_data():
               hook.execute()


A more basic integration is via the hook_scope context manager which simply
manages transaction scope (and records hook name, and timestamp)::

  >>> from unitdata import kv
  >>> db = kv()
  >>> with db.hook_scope('install'):
  ...    # do work, in transactional scope.
  ...    db.set('x', 1)
  >>> db.get('x')
  1


Usage
-----

Values are automatically json de/serialized to preserve basic typing
and complex data struct capabilities (dicts, lists, ints, booleans, etc).

Individual values can be manipulated via get/set::

   >>> kv.set('y', True)
   >>> kv.get('y')
   True

   # We can set complex values (dicts, lists) as a single key.
   >>> kv.set('config', {'a': 1, 'b': True'})

   # Also supports returning dictionaries as a record which
   # provides attribute access.
   >>> config = kv.get('config', record=True)
   >>> config.b
   True


Groups of keys can be manipulated with update/getrange::

   >>> kv.update({'z': 1, 'y': 2}, prefix="gui.")
   >>> kv.getrange('gui.', strip=True)
   {'z': 1, 'y': 2}

When updating values, its very helpful to understand which values
have actually changed and how have they changed. The storage
provides a delta method to provide for this::

   >>> data = {'debug': True, 'option': 2}
   >>> delta = kv.delta(data, 'config.')
   >>> delta.debug.previous
   None
   >>> delta.debug.current
   True
   >>> delta
   {'debug': (None, True), 'option': (None, 2)}

Note the delta method does not persist the actual change, it needs to
be explicitly saved via 'update' method::

   >>> kv.update(data, 'config.')

Values modified in the context of a hook scope retain historical values
associated to the hookname.

   >>> with db.hook_scope('config-changed'):
   ...      db.set('x', 42)
   >>> db.gethistory('x')
   [(1, u'x', 1, u'install', u'2015-01-21T16:49:30.038372'),
    (2, u'x', 42, u'config-changed', u'2015-01-21T16:49:30.038786')]

"""

import collections
import contextlib
import datetime
import itertools
import json
import os
import pprint
import sqlite3
import sys

__author__ = 'Kapil Thangavelu <kapil.foss@gmail.com>'


class Storage(object):
    """Simple key value database for local unit state within charms.

    Modifications are not persisted unless :meth:`flush` is called.

    To support dicts, lists, integer, floats, and booleans values
    are automatically json encoded/decoded.

    Note: to facilitate unit testing, ':memory:' can be passed as the
    path parameter which causes sqlite3 to only build the db in memory.
    This should only be used for testing purposes.
    """
    def __init__(self, path=None):
        self.db_path = path
        if path is None:
            if 'UNIT_STATE_DB' in os.environ:
                self.db_path = os.environ['UNIT_STATE_DB']
            else:
                self.db_path = os.path.join(
                    os.environ.get('CHARM_DIR', ''), '.unit-state.db')
        if self.db_path != ':memory:':
            with open(self.db_path, 'a') as f:
                os.fchmod(f.fileno(), 0o600)
        self.conn = sqlite3.connect('%s' % self.db_path)
        self.cursor = self.conn.cursor()
        self.revision = None
        self._closed = False
        self._init()

    def close(self):
        if self._closed:
            return
        self.flush(False)
        self.cursor.close()
        self.conn.close()
        self._closed = True

    def get(self, key, default=None, record=False):
        self.cursor.execute('select data from kv where key=?', [key])
        result = self.cursor.fetchone()
        if not result:
            return default
        if record:
            return Record(json.loads(result[0]))
        return json.loads(result[0])

    def getrange(self, key_prefix, strip=False):
        """
        Get a range of keys starting with a common prefix as a mapping of
        keys to values.

        :param str key_prefix: Common prefix among all keys
        :param bool strip: Optionally strip the common prefix from the key
            names in the returned dict
        :return dict: A (possibly empty) dict of key-value mappings
        """
        self.cursor.execute("select key, data from kv where key like ?",
                            ['%s%%' % key_prefix])
        result = self.cursor.fetchall()

        if not result:
            return {}
        if not strip:
            key_prefix = ''
        return dict([
            (k[len(key_prefix):], json.loads(v)) for k, v in result])

    def update(self, mapping, prefix=""):
        """
        Set the values of multiple keys at once.

        :param dict mapping: Mapping of keys to values
        :param str prefix: Optional prefix to apply to all keys in `mapping`
            before setting
        """
        for k, v in mapping.items():
            self.set("%s%s" % (prefix, k), v)

    def unset(self, key):
        """
        Remove a key from the database entirely.
        """
        self.cursor.execute('delete from kv where key=?', [key])
        if self.revision and self.cursor.rowcount:
            self.cursor.execute(
                'insert into kv_revisions values (?, ?, ?)',
                [key, self.revision, json.dumps('DELETED')])

    def unsetrange(self, keys=None, prefix=""):
        """
        Remove a range of keys starting with a common prefix, from the database
        entirely.

        :param list keys: List of keys to remove.
        :param str prefix: Optional prefix to apply to all keys in ``keys``
            before removing.
        """
        if keys is not None:
            keys = ['%s%s' % (prefix, key) for key in keys]
            self.cursor.execute('delete from kv where key in (%s)' % ','.join(['?'] * len(keys)), keys)
            if self.revision and self.cursor.rowcount:
                self.cursor.execute(
                    'insert into kv_revisions values %s' % ','.join(['(?, ?, ?)'] * len(keys)),
                    list(itertools.chain.from_iterable((key, self.revision, json.dumps('DELETED')) for key in keys)))
        else:
            self.cursor.execute('delete from kv where key like ?',
                                ['%s%%' % prefix])
            if self.revision and self.cursor.rowcount:
                self.cursor.execute(
                    'insert into kv_revisions values (?, ?, ?)',
                    ['%s%%' % prefix, self.revision, json.dumps('DELETED')])

    def set(self, key, value):
        """
        Set a value in the database.

        :param str key: Key to set the value for
        :param value: Any JSON-serializable value to be set
        """
        serialized = json.dumps(value)

        self.cursor.execute('select data from kv where key=?', [key])
        exists = self.cursor.fetchone()

        # Skip mutations to the same value
        if exists:
            if exists[0] == serialized:
                return value

        if not exists:
            self.cursor.execute(
                'insert into kv (key, data) values (?, ?)',
                (key, serialized))
        else:
            self.cursor.execute('''
            update kv
            set data = ?
            where key = ?''', [serialized, key])

        # Save
        if not self.revision:
            return value

        self.cursor.execute(
            'select 1 from kv_revisions where key=? and revision=?',
            [key, self.revision])
        exists = self.cursor.fetchone()

        if not exists:
            self.cursor.execute(
                '''insert into kv_revisions (
                revision, key, data) values (?, ?, ?)''',
                (self.revision, key, serialized))
        else:
            self.cursor.execute(
                '''
                update kv_revisions
                set data = ?
                where key = ?
                and   revision = ?''',
                [serialized, key, self.revision])

        return value

    def delta(self, mapping, prefix):
        """
        return a delta containing values that have changed.
        """
        previous = self.getrange(prefix, strip=True)
        if not previous:
            pk = set()
        else:
            pk = set(previous.keys())
        ck = set(mapping.keys())
        delta = DeltaSet()

        # added
        for k in ck.difference(pk):
            delta[k] = Delta(None, mapping[k])

        # removed
        for k in pk.difference(ck):
            delta[k] = Delta(previous[k], None)

        # changed
        for k in pk.intersection(ck):
            c = mapping[k]
            p = previous[k]
            if c != p:
                delta[k] = Delta(p, c)

        return delta

    @contextlib.contextmanager
    def hook_scope(self, name=""):
        """Scope all future interactions to the current hook execution
        revision."""
        assert not self.revision
        self.cursor.execute(
            'insert into hooks (hook, date) values (?, ?)',
            (name or sys.argv[0],
             datetime.datetime.utcnow().isoformat()))
        self.revision = self.cursor.lastrowid
        try:
            yield self.revision
            self.revision = None
        except Exception:
            self.flush(False)
            self.revision = None
            raise
        else:
            self.flush()

    def flush(self, save=True):
        if save:
            self.conn.commit()
        elif self._closed:
            return
        else:
            self.conn.rollback()

    def _init(self):
        self.cursor.execute('''
            create table if not exists kv (
               key text,
               data text,
               primary key (key)
               )''')
        self.cursor.execute('''
            create table if not exists kv_revisions (
               key text,
               revision integer,
               data text,
               primary key (key, revision)
               )''')
        self.cursor.execute('''
            create table if not exists hooks (
               version integer primary key autoincrement,
               hook text,
               date text
               )''')
        self.conn.commit()

    def gethistory(self, key, deserialize=False):
        self.cursor.execute(
            '''
            select kv.revision, kv.key, kv.data, h.hook, h.date
            from kv_revisions kv,
                 hooks h
            where kv.key=?
             and kv.revision = h.version
            ''', [key])
        if deserialize is False:
            return self.cursor.fetchall()
        return map(_parse_history, self.cursor.fetchall())

    def debug(self, fh=sys.stderr):
        self.cursor.execute('select * from kv')
        pprint.pprint(self.cursor.fetchall(), stream=fh)
        self.cursor.execute('select * from kv_revisions')
        pprint.pprint(self.cursor.fetchall(), stream=fh)


def _parse_history(d):
    return (d[0], d[1], json.loads(d[2]), d[3],
            datetime.datetime.strptime(d[-1], "%Y-%m-%dT%H:%M:%S.%f"))


class HookData(object):
    """Simple integration for existing hook exec frameworks.

    Records all unit information, and stores deltas for processing
    by the hook.

    Sample::

       from charmhelper.core import hookenv, unitdata

       changes = unitdata.HookData()
       db = unitdata.kv()
       hooks = hookenv.Hooks()

       @hooks.hook
       def config_changed():
           # View all changes to configuration
           for changed, (prev, cur) in changes.conf.items():
               print('config changed', changed,
                     'previous value', prev,
                     'current value',  cur)

           # Get some unit specific bookeeping
           if not db.get('pkg_key'):
               key = urllib.urlopen('https://example.com/pkg_key').read()
               db.set('pkg_key', key)

       if __name__ == '__main__':
           with changes():
               hook.execute()

    """
    def __init__(self):
        self.kv = kv()
        self.conf = None
        self.rels = None

    @contextlib.contextmanager
    def __call__(self):
        from charmhelpers.core import hookenv
        hook_name = hookenv.hook_name()

        with self.kv.hook_scope(hook_name):
            self._record_charm_version(hookenv.charm_dir())
            delta_config, delta_relation = self._record_hook(hookenv)
            yield self.kv, delta_config, delta_relation

    def _record_charm_version(self, charm_dir):
        # Record revisions.. charm revisions are meaningless
        # to charm authors as they don't control the revision.
        # so logic dependnent on revision is not particularly
        # useful, however it is useful for debugging analysis.
        charm_rev = open(
            os.path.join(charm_dir, 'revision')).read().strip()
        charm_rev = charm_rev or '0'
        revs = self.kv.get('charm_revisions', [])
        if charm_rev not in revs:
            revs.append(charm_rev.strip() or '0')
            self.kv.set('charm_revisions', revs)

    def _record_hook(self, hookenv):
        data = hookenv.execution_environment()
        self.conf = conf_delta = self.kv.delta(data['conf'], 'config')
        self.rels = rels_delta = self.kv.delta(data['rels'], 'rels')
        self.kv.set('env', dict(data['env']))
        self.kv.set('unit', data['unit'])
        self.kv.set('relid', data.get('relid'))
        return conf_delta, rels_delta


class Record(dict):

    __slots__ = ()

    def __getattr__(self, k):
        if k in self:
            return self[k]
        raise AttributeError(k)


class DeltaSet(Record):

    __slots__ = ()


Delta = collections.namedtuple('Delta', ['previous', 'current'])


_KV = None


def kv():
    global _KV
    if _KV is None:
        _KV = Storage()
    return _KV
