text: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  #
  # Copyright 2014-2015 Canonical Limited.
  #
  # This file is part of charm-helpers.
  #
  # charm-helpers is free software: you can redistribute it and/or modify
  # it under the terms of the GNU Lesser General Public License version 3 as
  # published by the Free Software Foundation.
  #
  # charm-helpers 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 Lesser General Public License for more details.
  #
  # You should have received a copy of the GNU Lesser General Public License
  # along with charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
  #
  #
  # 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 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 automatically committed at hook exit. That's
      currently regardless of exit code.
  
      To support dicts, lists, integer, floats, and booleans values
      are automatically json encoded/decoded.
      """
      def __init__(self, path=None):
          self.db_path = path
          if path is None:
              self.db_path = os.path.join(
                  os.environ.get('CHARM_DIR', ''), '.unit-state.db')
          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 _scoped_query(self, stmt, params=None):
          if params is None:
              params = []
          return stmt, params
  
      def get(self, key, default=None, record=False):
          self.cursor.execute(
              *self._scoped_query(
                  '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):
          stmt = "select key, data from kv where key like '%s%%'" % key_prefix
          self.cursor.execute(*self._scoped_query(stmt))
          result = self.cursor.fetchall()
  
          if not result:
              return None
          if not strip:
              key_prefix = ''
          return dict([
              (k[len(key_prefix):], json.loads(v)) for k, v in result])
  
      def update(self, mapping, prefix=""):
          for k, v in mapping.items():
              self.set("%s%s" % (prefix, k), v)
  
      def unset(self, key):
          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 set(self, key, value):
          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:
              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
  