from datetime import datetime
from cStringIO import StringIO

import hashlib
import psycopg2

from config import *

db_list = [psycopg2.connect(database=db['database'], user=db['user'],
                            host=db['host'], password=db['password'])
           for db in DATABASE['list']]
with_prefix = lambda name: '%s%s' % (DATABASE['prefix'], name)


def get_shard_number(user_id):
    return int(hashlib.sha1(user_id)
               .hexdigest(), 16) % len(db_list)

# Takes one argument: model
fn_get_fields = lambda m: [e for e in m._meta.fields.keys() if e != 'id']


class Core(object):
    @classmethod
    def add(cls, db_table, *args, **kw):
        if not hasattr(cls, 'cache'):
            setattr(cls, 'cache', [[] for x in xrange(len(db_list))])
        kw.update(created_at=datetime.now().strftime('%Y-%m-%d %H:%M:%S'))
        (cls.cache[get_shard_number(kw['user'])]
            .append(cls.build_record(**kw)))

    #TODO: Please, override this method in child class
    @classmethod
    def build_record(cls, *args, **kw):
        return 'must be return str'

    @classmethod
    def copy_from(cls):
        db_table = with_prefix(cls.__name__.lower())
        for (i, data) in enumerate(cls.cache):
            db_list[i].copy_from(StringIO('\n'.join(data)), db_table,
                                 columns=fn_get_fields(cls))
        del cls.cache


class Install(Core):
    @classmethod
    def build_record(cls, user, created_at, user_level='NULL', *args, **kw):
        return '\t'.join([locals()[e] for e in fn_get_fields(cls)])


class Visit(Core):
    @classmethod
    def build_record(cls, user, created_at, user_level='NULL', *args, **kw):
        return '\t'.join([locals()[e] for e in fn_get_fields(cls)])


class Exit(Core):
    @classmethod
    def build_record(cls, delta, user, created_at, user_level='NULL',
                     *args, **kw):
        return '\t'.join([locals()[e] for e in fn_get_fields(cls)])


class Payment(Core):
    @classmethod
    def build_record(cls, currency, user, created_at, user_level='NULL',
                     *args, **kw):
        return '\t'.join([locals()[e] for e in fn_get_fields(cls)])


class Custom(Core):
    @classmethod
    def build_record(cls, created_at, user, name, user_level='NULL',
                     name1='NULL', name2='NULL', name3='NULL',
                     value=0, *args, **kw):
        return '\t'.join([locals()[e] for e in fn_get_fields(cls)])