self._init_property_tables(properties)

    def _init_morg_table(self):
        '''Create Morg's identification table.

        This internal method creates and populates the <tt>morg</tt>
        table, which is used to identify SQLite files as "belonging" to


        Morg.
























        '''
        logger.info('creating morg table')
        wm = watermark()

        wm.dump()



        self.execute(wm.create())

        logger.info('populating morg table')




        columns = wm.columns()









        insert  = ('insert into morg ({}) values ({})'.
                   format(','.join(columns), ','.join('?' * len(columns))))
        self.execute(insert, tuple(wm))

    def _sanity_check(self, tasks_file):
        '''Try and confirm we're dealing with a Morg database.

        @param tasks_file (string) Name of SQLite file.

        Morg creates a table named <tt>morg</tt> in which it stores the

        logger.debug('morg table has {} rows'.format(n))
        if (n < 1):
            raise sanity_check_error(tasks_file, 'morg table has no data')
        if (n > 1):
            raise sanity_check_error(tasks_file,
                                     'morg table has too much data')

        wm = watermark(morg[0])

        wm.dump()

        if (not wm):

            raise sanity_check_error(tasks_file, 'magic phrase mismatch')
        logger.info('looks like this is a morg database')

    def _init_task_table(self):
        '''Create the task table if necessary.

        This internal method sets up the <tt>task</tt> table, which
        simply records all the tasks stored in the database.

        try:
            logger.debug('executing query: {}'.format(query))
            cursor = self._db.cursor()
            return list(cursor.execute(query, bindings))
        except apsw.Error, e:
            logger.error('failed query: {}; reason: {}'.format(query, e))
            raise sql_error(query, e)

#----------------------- WATERMARK ENCAPSULATION ------------------------

class watermark:
    '''Helper class for Morg's database watermark.

    This class eases creation and verification of the <tt>morg</tt>
    watermark table so that Morg can identify SQLite files as "belonging"
    to it.

    '''
    def __init__(self, metadata = None):
        '''Construct a watermark object.

        @param metadata (tuple or dict) Watermark table's data.

        The <tt>morg</tt> table contains exactly one row, which has the
        following columns:

        @li <tt>schema_version</tt>
        @li <tt>timestamp</tt>
        @li <tt>hostname</tt>
        @li <tt>username</tt>
        @li <tt>magic_phrase</tt>

        The schema version is an integer that helps track the structure
        of the database. It can be used, for example, to upgrade older
        data models to more current ones.

        The time stamp records the creation time (GMT) of the database in
        the format <tt>yyyy-mm-dd HH:MM:SS</tt>.

        The host name records the fully qualified domain name of the
        machine on which this Morg database was created.

        The user name identifies the login name of the user who created
        the database. If this cannot be determined, this field will be
        recorded as <tt>unidentifiable_user</tt>.

        Finally, the magic phrase is the SHA-1 ID of the string produced
        by concatenating the schema version, time stamp, host name, user
        name, and a hard-coded identification string used by Morg.

        If the metadata parameter is not given, this constructor will use
        default values for the above-mentioned fields of the watermark
        table. If it is given in the form of a dict, we expect the keys
        to be the column names stated above and the values to be as
        described above. If given as a tuple, we expect the tuple to
        contain only the values.

        '''
        self._metadata = {}
        self._metadata['schema_version'] = database.SCHEMA_VERSION
        try:
            self._metadata['timestamp' ] = time.strftime('%Y-%m-%d %H:%M:%S',
                                                        time.gmtime())
        except Exception:
            logger.warning('unable to get current time')
            self._metadata['timestamp' ] = '0000-00-00 00:00:00'
        try:
            self._metadata['hostname'  ] = socket.getfqdn(socket.gethostname())
        except Exception:
            logger.warning('unable to get hostname')
            self._metadata['hostname'  ] = 'unknown.host.name'
        try:
            self._metadata['username'  ] = getpass.getuser()
        except Exception:
            logger.warning('unable to get current login name')
            self._metadata['username'  ] = 'anonymous'
        self._metadata['magic_phrase'  ] = self.magic_phrase()

        if (isinstance(metadata, dict)):
            for key in self._metadata  :
                if (key  in  metadata) :
                    self._metadata[key] = metadata[key]

        if (isinstance(metadata,tuple)):
            for key, val in zip(self.columns(), metadata):
                self._metadata[key] = val

    def __iter__(self):
        '''Iterator over watermark metadata (in correct order).'''
        class _iterator_adaptor:
            def __init__(self, wm):
                self._metadata = []
                for key in wm.columns():
                    self._metadata.append((key, wm._metadata[key]))
                self._iter = iter(self._metadata)

            def next(self):
                column, value = self._iter.next()
                return  value

        return _iterator_adaptor(self)

    def __nonzero__(self):
        '''Confirm that stored and computed magic phrases match.'''
        stored   = self._metadata['magic_phrase']
        computed = self.magic_phrase()
        logger.debug('magic phrase: stored = {}, computed = {}'.
                     format(stored, computed))
        return stored == computed

    def columns(self):
        '''Return column names of <tt>morg</tt> table in correct order.'''
        return ('schema_version',
                'timestamp',
                'hostname' ,
                'username' ,
                'magic_phrase')

    def magic_phrase(self):
        '''Encode metadata into an identity string.'''
        metadata = []
        for key in self.columns()[:-1]:
            metadata.append(str(self._metadata[key]))
        metadata.append(database.MAGIC_PHRASE)
        return hashlib.sha1('\n'.join(metadata)).hexdigest()

    def create(self):
        '''Return SQL statement for creating watermark table.'''
        return '''create table if not exists morg(
                      schema_version  integer,
                      timestamp       text,
                      hostname        text,
                      username        text,
                      magic_phrase    text)'''

    def sql(self):
        '''Return SQL statements for creating and populating watermark table.'''
        insert = ('insert into morg (\n        {})\n    values (\n        {})'.
                  format(',\n        '.join(self.columns()),
                         ',\n        '.join(map(lambda v: ("'{}'".format(v)
                                                           if isinstance(v, str)
                                                           else str(v)),
                                                tuple(self)))))
        return '{};\n{};\n'.format(self.create(), insert)

    def dump(self):
        '''Debug support.'''
        for key, val in self._metadata.iteritems():
            logger.debug('{} = {}'.format(key, val))

#------------------------------- HELPERS --------------------------------

def range_constraint(column_name, column_type, range_spec):
    '''Parse range specification and return column constraint clause.

    @param  column_name (string) Name of column that needs a constraint.

    try:
        return ('check ({} in ({}))'.
                format(column_name,
                       ','.join(map(fmt, range_spec.split(',')))))
    except Exception, e:
        raise property_error(column_name, column_type, range_spec, e)



























#------------------------------------------------------------------------

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  *  Create <tt>task</tt> table on database init.
  *  Create <tt>property</tt> table on database init.
  *  Add default properties dict.
  *  Create <tt>property_NNN</tt> tables on database init.
  *  Implement sanity check on database initialization.
  *  Update database constructor doc string.
  *  Use the BETWEEN operator in property range constraints.
  *  Implement a watermark class to ease verification and "Morgification."

<h2>PENDING</h2>


  *  The watermark table should be created and populated in a transaction.
  *  Update doc strings to reflect recent changes about the watermark.
  *  Pass database to all commands' <tt>__call__</tt> method.
  *  Implement <tt>new</tt> command.