from collections import defaultdict

from datetime import datetime
from flask.ext.sqlalchemy import SQLAlchemy, BaseQuery
from flask import g

from sqlalchemy import orm

db = SQLAlchemy()


# define models


class Project(db.Model):

    _to_serialize = ("id", "name", "password", "contact_email",
            "members", "active_members", "balance")

    id = db.Column(db.String(64), primary_key=True)

    name = db.Column(db.UnicodeText)
    password = db.Column(db.String(128))
    contact_email = db.Column(db.String(128))
    members = db.relationship("Person", backref="project")

    @property
    def active_members(self):
        return [m for m in self.members if m.activated]

    @property
    def balance(self):

        balances, should_pay, should_receive = (defaultdict(int)
            for time in (1, 2, 3))

        # for each person
        for person in self.members:
            # get the list of bills he has to pay
            bills = Bill.query.filter(Bill.owers.contains(person))
            for bill in bills.all():
                if person != bill.payer:
                    share = bill.pay_each() * person.weight
                    should_pay[person] += share
                    should_receive[bill.payer] += share

        for person in self.members:
            balance = should_receive[person] - should_pay[person]
            balances[person.id] = balance

        return balances

    def get_transactions_to_settle_bill(self):
        """Return a list of transactions that could be made to settle the bill"""
        #cache value for better performance
        balance = self.balance
        credits, debts, transactions = [],[],[]
        # Create lists of credits and debts
        for person in self.members:
            if balance[person.id] > 0:
                credits.append({"person": person, "balance": balance[person.id]})
            elif balance[person.id] < 0:
                debts.append({"person": person, "balance": -balance[person.id]})
        # Try and find exact matches
        for credit in credits:
            match = self.exactmatch(round(credit["balance"], 2), debts)
            if match:
                for m in match:
                    transactions.append({"ower": m["person"], "receiver": credit["person"], "amount": m["balance"]})
                    debts.remove(m)
                credits.remove(credit)
        # Split any remaining debts & credits
        while credits and debts:
            if credits[0]["balance"] > debts[0]["balance"]:
                transactions.append({"ower": debts[0]["person"], "receiver": credits[0]["person"], "amount": debts[0]["balance"]})
                credits[0]["balance"] = credits[0]["balance"] - debts[0]["balance"]
                del debts[0]
            else:
                transactions.append({"ower": debts[0]["person"], "receiver": credits[0]["person"], "amount": credits[0]["balance"]})
                debts[0]["balance"] = debts[0]["balance"] - credits[0]["balance"]
                del credits[0]
        return transactions

    def exactmatch(self, credit, debts):
        """Recursively try and find subsets of 'debts' whose sum is equal to credit"""
        if not debts:
            return None
        if debts[0]["balance"] > credit:
            return self.exactmatch(credit, debts[1:])
        elif debts[0]["balance"] == credit:
            return [debts[0]]
        else:
            match = self.exactmatch(credit-debts[0]["balance"], debts[1:])
            if match:
                match.append(debts[0])
            else:
                match = self.exactmatch(credit, debts[1:])
            return match

    def has_bills(self):
        """return if the project do have bills or not"""
        return self.get_bills().count() > 0

    def get_bills(self):
        """Return the list of bills related to this project"""
        return Bill.query.join(Person, Project)\
            .filter(Bill.payer_id == Person.id)\
            .filter(Person.project_id == Project.id)\
            .filter(Project.id == self.id)\
            .order_by(Bill.date.desc())

    def remove_member(self, member_id):
        """Remove a member from the project.

        If the member is not bound to a bill, then he is deleted, otherwise
        he is only deactivated.

        This method returns the status DELETED or DEACTIVATED regarding the
        changes made.
        """
        try:
            person = Person.query.get(member_id, self)
        except orm.exc.NoResultFound:
            return None
        if not person.has_bills():
            db.session.delete(person)
            db.session.commit()
        else:
            person.activated = False
            db.session.commit()
        return person

    def remove_project(self):
        db.session.delete(self)
        db.session.commit()

    def __repr__(self):
        return "<Project %s>" % self.name


class Person(db.Model):

    class PersonQuery(BaseQuery):
        def get_by_name(self, name, project):
            return Person.query.filter(Person.name == name)\
                .filter(Project.id == project.id).one()

        def get(self, id, project=None):
            if not project:
                project = g.project
            return Person.query.filter(Person.id == id)\
                .filter(Project.id == project.id).one()

    query_class = PersonQuery

    _to_serialize = ("id", "name", "activated")

    id = db.Column(db.Integer, primary_key=True)
    project_id = db.Column(db.String(64), db.ForeignKey("project.id"))
    bills = db.relationship("Bill", backref="payer")

    name = db.Column(db.UnicodeText)
    weight = db.Column(db.Float, default=1)
    activated = db.Column(db.Boolean, default=True)

    def has_bills(self):
        """return if the user do have bills or not"""
        bills_as_ower_number = db.session.query(billowers)\
            .filter(billowers.columns.get("person_id") == self.id)\
            .count()
        return bills_as_ower_number != 0 or len(self.bills) != 0

    def __str__(self):
        return self.name

    def __repr__(self):
        return "<Person %s for project %s>" % (self.name, self.project.name)

# We need to manually define a join table for m2m relations
billowers = db.Table('billowers',
    db.Column('bill_id', db.Integer, db.ForeignKey('bill.id')),
    db.Column('person_id', db.Integer, db.ForeignKey('person.id')),
)


class Bill(db.Model):

    class BillQuery(BaseQuery):

        def get(self, project, id):
            try:
                return self.join(Person, Project)\
                    .filter(Bill.payer_id == Person.id)\
                    .filter(Person.project_id == Project.id)\
                    .filter(Project.id == project.id)\
                    .filter(Bill.id == id).one()
            except orm.exc.NoResultFound:
                return None

        def delete(self, project, id):
            bill = self.get(project, id)
            if bill:
                db.session.delete(bill)
            return bill

    query_class = BillQuery

    _to_serialize = ("id", "payer_id", "owers", "amount", "date", "what")

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

    payer_id = db.Column(db.Integer, db.ForeignKey("person.id"))
    owers = db.relationship(Person, secondary=billowers)

    amount = db.Column(db.Float)
    date = db.Column(db.Date, default=datetime.now)
    what = db.Column(db.UnicodeText)

    archive = db.Column(db.Integer, db.ForeignKey("archive.id"))

    def pay_each(self):
        """Compute what each person has to pay"""
	if self.owers:
                # FIXME: SQL might dot that more efficiently
		return self.amount / sum(i.weight for i in self.owers)
	else:
		return 0

    def __repr__(self):
        return "<Bill of %s from %s for %s>" % (self.amount,
                self.payer, ", ".join([o.name for o in self.owers]))


class Archive(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    project_id = db.Column(db.String(64), db.ForeignKey("project.id"))
    name = db.Column(db.UnicodeText)

    @property
    def start_date(self):
        pass

    @property
    def end_date(self):
        pass

    def __repr__(self):
        return "<Archive>"