from datetime import datetime
from contextlib import contextmanager

import sqlalchemy as sa
import sqlalchemy.ext.declarative
from sqlalchemy.exc import SQLAlchemyError
from sqlalchemy import Table, Column, ForeignKey
from sqlalchemy import Integer, String, Boolean, DateTime
from sqlalchemy.orm import relationship

from sqlalchemy_utils import force_auto_coercion
from sqlalchemy_utils.types.password import PasswordType

from pos.logging import get_logger


# The database URL must follow RFC 1738 in the form
# dialect+driver://username:password@host:port/database
ENGINE_GENERIC = "{engine}://{user}:{password}@{host}:{port}/{database}"\
                 "?charset=utf8"
ENGINE_SQLITE = "sqlite:///{path}"
ENGINE_SQLITE_MEMORY = "sqlite://"

PASSWORD_SCHEMES = ['pbkdf2_sha512']


Base = sqlalchemy.ext.declarative.declarative_base()
log = get_logger('database')

force_auto_coercion()


class Database:
    """
    Handle database operations."
    """

    Session = None
    engine = None

    def __init__(self, **kwargs):
        """
        Initialize database connection.

        :param engine: The SQLAlchemy database backend in the form
                       dialect+driver where dialect is the name of a SQLAlchemy
                       dialect (sqlite, mysql, postgresql, oracle or mssql) and
                       driver is the name of the DBAPI in all lowercase
                       letters. If driver is not specified the default DBAPI
                       will be imported if available.
        :param path: Only for SQLite. Path to database. If not specified the
                     database will be kept in memory (should be used only for
                     testing).
        :param host:
        :param port:
        :param database:
        :param user:
        :param password:
        """

        if kwargs['engine'] == 'sqlite':
            if 'path' in kwargs:
                url = ENGINE_SQLITE.format(path=kwargs['path'])
            else:
                url = ENGINE_SQLITE_MEMORY
        else:
            url = ENGINE_GENERIC.format(**kwargs)

        self.engine = sa.create_engine(url)
        self.Session = sa.orm.sessionmaker(
            bind=self.engine,
            expire_on_commit=False
        )

        Base.metadata.create_all(self.engine)

    @contextmanager
    def get_session(self):
        session = self.Session()
        try:
            yield session
        except SQLAlchemyError as e:
            log.critical("Error performing transaction:")
            log.critical(e)
            session.rollback()
        else:
            session.commit()
        finally:
            session.close()


class User(Base):
    __tablename__ = 'users'
    uid = Column(Integer, primary_key=True)
    username = Column(String, nullable=False, unique=True)
    password = Column(PasswordType(schemes=PASSWORD_SCHEMES), nullable=False)
    is_active = Column(Boolean, nullable=False, server_default='1')
    is_authenticated = Column(Boolean, nullable=False, server_default='0')
    created_at = Column(DateTime, nullable=False, default=datetime.now)

    def get_id(self):
        return u'{}'.format(self.uid)


class Event(Base):
    __tablename__ = 'events'
    uid = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    starts_at = Column(DateTime, nullable=False, default=datetime.now)
    ends_at = Column(DateTime)
    created_at = Column(DateTime, nullable=False, default=datetime.now)

    transactions = relationship('Transaction', lazy='joined')


class ProductCategory(Base):
    __tablename__ = 'product_categories'
    uid = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    sort = Column(Integer, nullable=False, server_default='0')
    created_at = Column(DateTime, nullable=False, default=datetime.now)

    products = relationship('Product', lazy='joined')


class Product(Base):
    __tablename__ = 'products'
    uid = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    price = Column(Integer, nullable=False)
    sort = Column(Integer, nullable=False, server_default='0')
    category_uid = Column(Integer, ForeignKey('product_categories.uid'),
                          nullable=False)
    is_active = Column(Boolean, nullable=False, server_default='1')
    created_at = Column(DateTime, nullable=False, default=datetime.now)

    category = relationship('ProductCategory', lazy='joined')


order_entry_association = Table(
    'order_entry_associations', Base.metadata,
    Column('transaction_uid', Integer, ForeignKey('transactions.uid')),
    Column('order_uid', Integer, ForeignKey('orders.uid'))
    )


class Transaction(Base):
    __tablename__ = 'transactions'
    uid = Column(Integer, primary_key=True)
    event_uid = Column(Integer, ForeignKey('events.uid'), nullable=False)
    created_at = Column(DateTime, nullable=False, default=datetime.now)

    event = relationship('Event')
    orders = relationship('Order', lazy='joined',
                          secondary=order_entry_association)


class Order(Base):
    __tablename__ = 'orders'
    uid = Column(Integer, primary_key=True)
    product_uid = Column(Integer, ForeignKey('products.uid'), nullable=False)
    quantity = Column(Integer, nullable=False)

    product = relationship('Product', lazy='joined')