''' SQL conventions and custom Encoders '''

import json

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.schema import MetaData
from sqlalchemy.types import TypeDecorator, Unicode

# Recommended naming convention used by Alembic, as various different database
# providers will autogenerate vastly different names making migrations more
# difficult. See: http://alembic.zzzcomputing.com/en/latest/naming.html
NAMING_CONVENTION = {
    "ix": "ix_%(column_0_label)s",
    "uq": "uq_%(table_name)s_%(column_0_name)s",
    "ck": "ck_%(table_name)s_%(constraint_name)s",
    "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
    "pk": "pk_%(table_name)s"
    }

metadata = MetaData(naming_convention=NAMING_CONVENTION)
Base = declarative_base(metadata=metadata)


class JsonEncoder(TypeDecorator):
    ''' Custom type for storing data structures as json-encoded string. '''

    impl = Unicode

    def process_bind_param(self, value, dialect):
        ''' inbound (to database) '''
        if value is not None:
            value = json.dumps(value)
        return value

    def process_result_value(self, value, dialect):
        ''' outbound (from database) '''
        if value is not None:
            value = json.loads(value)
        return value