from sqlalchemy import types as T
from sqlalchemy import sql, Index, Column, ForeignKey, create_engine
from sqlalchemy.orm import relationship, backref, scoped_session, sessionmaker,\
                           column_property
from sqlalchemy.ext.declarative import declarative_base, declared_attr
from sqlalchemy.ext.hybrid import hybrid_property

import datetime
import decimal
from functools import partial
from collections import namedtuple

__all__ = ["Category", "SingleExpense", "ConstExpense", "CatExpense", "MonthExpense",
           "Session"]

#
# DB Setup
#

engine = create_engine("sqlite:///test.sqlite")
engine.echo = True

Session = scoped_session(sessionmaker(bind=engine))

#
# Global definitions
#

class Base(object):
    @declared_attr
    def __tablename__ (cls):
        return cls.__name__.lower()

    id = Column(T.Integer, primary_key=True)

    query = Session.query_property()

    @classmethod
    def get_by (cls, *args, **kwargs):
        return cls.query.filter_by(*args, **kwargs).first()

    @classmethod
    def get (cls, *args, **kwargs):
        return cls.query.get(*args, **kwargs)


Base = declarative_base(cls=Base)

ReqColumn = partial(Column, nullable = False)
ExpNum = T.Numeric(scale = 2, precision = 10)

def to_exp(d):
    """Converts decimal into expense"""
    return d.quantize(decimal.Decimal('.01'), rounding = decimal.ROUND_UP)

#
# Database Entities
#

class Category (Base):
    name = ReqColumn(T.Unicode(50), unique = True)
    parent_id = Column(T.Integer, ForeignKey('category.id'))

    children = relationship('Category',
                            backref=backref('parent', remote_side="Category.id"))

    def __repr__ (self):
        if self.parent:
            return '<Category "%s" of "%s">' % (self.name, self.parent.name)
        else:
            return '<Category "%s">' % self.name

class Expense (Base):
    __abstract__ = True

    description = Column(T.Unicode(50))
    expense     = ReqColumn(ExpNum)

    @declared_attr
    def category_id(cls):
        return ReqColumn(T.Integer, ForeignKey(Category.id))

    @declared_attr
    def category(cls):
        return relationship(Category, innerjoin = True)

class SingleExpense (Expense):
    year = ReqColumn(T.Integer)
    month = ReqColumn(T.SmallInteger)
    day = ReqColumn(T.SmallInteger)

    @classmethod
    def of_month (cls, month, year):
        comp = sql.and_(
                cls.month == month,
                cls.year == year)

        return cls.query.filter(comp)

    @property
    def date (self):
        return datetime.date(self.year, self.month, self.day)

    @date.setter
    def date (self, d):
        self.year = d.year
        self.month = d.month
        self.day = d.day

class ConstExpense (Expense):
    months  = ReqColumn(T.SmallInteger)
    start   = ReqColumn(T.Date, index = True)
    end     = ReqColumn(T.Date, index = True)
    prev_id = Column(T.Integer, ForeignKey('constexpense.id'))

    prev = relationship('ConstExpense', remote_side = "ConstExpense.id", uselist = False,
                         backref=backref('next', uselist = False))

    @property
    def monthly(self):
        return to_exp(self.expense / self.months)
    
    @classmethod
    def of_month (cls, month, year):
        d = datetime.date(year, month, 1)
        return cls.query.filter(sql.between(d, cls.start, cls.end))

#
# Work entities (not stored in DB)
#
class CatExpense (namedtuple('CatExpense', 'cat expense exps')):
    __slots__ = ()

    @property
    def all (self):
        return self.exps.order_by(SingleExpense.day).all()

class MonthExpense (namedtuple('MonthExpense', 'date catexps')):
    
    def __init__ (self, *args, **kwargs):
        self._consts = None
        super(MonthExpense, self).__init__(*args, **kwargs)

    @property
    def consts (self):
        if self._consts is None:
            self._consts = ConstExpense.of_month(self.date.month, self.date.year).all()

        return self._consts

    @property
    def constsum (self):
        s = sum(c.monthly for c in self.consts)
        return s or 0

    @property
    def sum (self):
        return self.constsum + sum(x.expense for x in self.catexps)

    @property
    def all (self):
        return SingleExpense.of_month(self.date.month, self.date.year).order_by(SingleExpense.day).all()

    def __str__ (self):
        return '<MonthExpense of "%s": %s>' % (self.date, self.sum)

#
# Extra indizes have to be here
#

Index('idx_single_date', SingleExpense.year, SingleExpense.month)
Index('idx_start_end', ConstExpense.start, ConstExpense.end)

if __name__ == "__main__":
    Base.metadata.create_all(engine)