django-oscar-accounts2 0.1.0
Managed accounts for django-oscar
License: BSD

===========================
Managed accounts for Django
===========================

A 'managed account' is an allocation of money that can be debited and credited.
This package provides managed account functionality for use with the e-commerce
framework `Oscar`_.  It can also be used standalone without Oscar.

.. _`Oscar`: https://github.com/django-oscar/django-oscar

Accounts can be used to implement a variety of interesting components,
including:

* Giftcards
* Web accounts
* Loyalty schemes

Basically anything that involves tracking the movement of funds within a closed
system.

This package uses `double-entry bookkeeping`_ where every transaction is
recorded twice (once for the source and once for the destination).  This
ensures the books always balance and there is full audit trail of all
transactional activity.

If your project manages money, you should be using a library like this.  Your
finance people will thank you.


.. image:: https://travis-ci.org/crgwbr/django-oscar-accounts2.svg?branch=master
    :target: https://travis-ci.org/crgwbr/django-oscar-accounts2

.. image:: http://codecov.io/github/crgwbr/django-oscar-accounts2/coverage.svg?branch=master
    :alt: Coverage
    :target: http://codecov.io/github/crgwbr/django-oscar-accounts2?branch=master

.. image:: https://requires.io/github/crgwbr/django-oscar-accounts2/requirements.svg?branch=master
     :target: https://requires.io/github/crgwbr/django-oscar-accounts2/requirements/?branch=master
     :alt: Requirements Status

.. image:: https://img.shields.io/pypi/v/django-oscar-accounts2.svg
    :target: https://pypi.python.org/pypi/django-oscar-accounts2/


.. _double-entry bookkeeping: http://en.wikipedia.org/wiki/Double-entry_bookkeeping_system


Features
--------

* An account has a credit limit which defaults to zero.  Accounts can be set up
  with no credit limit so that they are a 'source' of money within the system.
  At least one account must be set up without a credit limit in order for money
  to move around the system.

* Accounts can have:
  - No users assigned
  - A single "primary" user - this is the most common case
  - A set of users assigned

* A user can have multiple accounts

* An account can have a start and end date to allow its usage in a limited time
  window

* An account can be restricted so that it can only be used to pay for a range of
  products.

* Accounts can be categorised

Screenshots
-----------

.. image:: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-accounts.thumb.png
    :alt: Dashboard account list
    :target: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-accounts.png

.. image:: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-form.thumb.png
    :alt: Create new account
    :target: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-form.png

.. image:: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-transfers.thumb.png
    :alt: Dashboard transfer list
    :target: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-transfers.png

.. image:: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-detail.thumb.png
    :alt: Dashboard account detail
    :target: https://github.com/crgwbr/django-oscar-accounts2/raw/master/screenshots/dashboard-detail.png


Installation
------------

Install using pip:

.. code-block:: bash

        pip install django-oscar-accounts2

and add `oscar_accounts` to `INSTALLED_APPS`.  Runnning ``manage.py migrate
oscar_accounts`` will create the appropriate database tables. To create initial
some core accounts and account-types use ``manage.py oscar_accounts_init``.
The names of these accounts can be controlled using settings (see below).

If running with Oscar, add an additional path to your `TEMPLATE_DIRS`:

.. code-block:: python

    from accounts import TEMPLATE_DIR as ACCOUNTS_TEMPLATE_DIR

    TEMPLATE_DIRS = (
        ...
        ACCOUNTS_TEMPLATE_DIR)

This allows the templates to be customised by overriding blocks instead of
replacing the entire template.

In order to make the accounts accessible via the Oscar dashboard you need to
append it to your `OSCAR_DASHBOARD_NAVIGATION`

.. code-block:: python

    from oscar.defaults import *

    OSCAR_DASHBOARD_NAVIGATION.append(
        {
            'label': 'Accounts',
            'icon': 'icon-globe',
            'children': [
                {
                    'label': 'Accounts',
                    'url_name': 'accounts-list',
                },
                {
                    'label': 'Transfers',
                    'url_name': 'transfers-list',
                },
                {
                    'label': 'Deferred income report',
                    'url_name': 'report-deferred-income',
                },
                {
                    'label': 'Profit/loss report',
                    'url_name': 'report-profit-loss',
                },
            ]
        })


Furthermore you need to add the url-pattern to your `urls.py`

.. code-block:: python

    from oscar_accounts.dashboard.app import application as accounts_app

    # ...

    urlpatterns = [
        ...
        url(r'^dashboard/accounts/', include(accounts_app.urls)),
    ]


You should also set-up a cronjob that calls::

    ./manage.py close_expired_accounts

to close any expired accounts and transfer their funds to the 'expired'
account.

API
---

Create account instances using the manager:

.. code-block:: python

    from decimal import Decimal
    import datetime

    from django.contrib.auth.models import User

    from oscar_accounts import models

    anonymous_account = models.Account.objects.create()

    barry = User.objects.get(username="barry")
    user_account = models.Account.objects.create(primary_user=barry)

    no_credit_limit_account = models.Account.objects.create(credit_limit=None)
    credit_limit_account = models.Account.objects.create(credit_limit=Decimal('1000.00'))

    today = datetime.date.today()
    next_week = today + datetime.timedelta(days=7)
    date_limited_account = models.Account.objects.create(
        start_date=today, end_date=next_week)


Transfer funds using the facade:

.. code-block:: python

    from oscar_accounts import facade

    staff_member = User.objects.get(username="staff")
    trans = facade.transfer(source=no_credit_limit_account,
                            destination=user_account,
                            amount=Decimal('10.00'),
                            user=staff_member)

Reverse transfers:

.. code-block:: python

    facade.reverse(trans, user=staff_member,
                   description="Just an example")

If the proposed transfer is invalid, an exception will be raised.  All
exceptions are subclasses of `oscar_accounts.exceptions.AccountException`.
Your client code should look for exceptions of this type and handle them
appropriately.

Client code should only use the `oscar_accounts.models.Budget` class and the
two functions from `oscar_accounts.facade` - nothing else should be required.

Error handling
--------------

Note that the transfer operation is wrapped in its own database transaction to
ensure that only complete transfers are written out.  When using Django's
transaction middleware, you need to be careful.  If you have an unhandled
exception,  then account transfers will still be committed even though nothing
else will be.  To handle this, you need to make sure that, if an exception
occurs during your post-payment code, then you roll-back any transfers.

Here's a toy example:


.. code-block:: python

    from oscar_accounts import facade

    def submit(self, order_total):
        # Take payment first
        transfer = facade.transfer(self.get_user_account(),
                                   self.get_merchant_account(),
                                   order_total)
        # Create order models
        try:
            self.place_order()
        except Exception, e:
            # Something went wrong placing the order.  Roll-back the previous
            # transfer
            facade.reverse(transfer)

In this situation, you'll end up with two transfers being created but no order.
While this isn't ideal, it's the best way of handling exceptions that occur
during order placement.

Multi-transfer payments
-----------------------

Projects will often allow users to have multiple accounts and pay for an order
using more than one.  This will involve several transfers and needs some
careful handling in your application code.

It normally makes sense to write your own wrapper around the accounts API to
encapsulate your business logic and error handling.  Here's an example:


.. code-block:: python

    from decimal import Decimal as D
    from oscar_accounts import models, exceptions, facade


    def redeem(order_number, user, amount):
        # Get user's non-empty accounts ordered with the first to expire first
        accounts = models.Account.active.filter(
            user=user, balance__gt=0).order_by('end_date')

        # Build up a list of potential transfers that cover the requested amount
        transfers = []
        amount_to_allocate = amount
        for account in accounts:
            to_transfer = min(account.balance, amount_to_allocate)
            transfers.append((account, to_transfer))
            amount_to_allocate -= to_transfer
            if amount_to_allocate == D('0.00'):
                break
        if amount_to_allocate > D('0.00'):
            raise exceptions.InsufficientFunds()

        # Execute transfers to some 'Sales' account
        destination = models.Account.objects.get(name="Sales")
        completed_transfers = []
        try:
            for account, amount in transfers:
                transfer = facade.transfer(
                    account, destination, amount, user=user,
                    description="Order %s" % order_number)
                completed_transfers.append(transfer)
        except exceptions.AccountException, transfer_exc:
            # Something went wrong with one of the transfers (possibly a race condition).
            # We try and roll back all completed ones to get us back to a clean state.
            try:
                for transfer in completed_transfers:
                    facade.reverse(transfer)
            except Exception, reverse_exc:
                # Uh oh: No man's land.  We could be left with a partial
                # redemption. This will require an admin to intervene.  Make
                # sure your logger mails admins on error.
                logger.error("Order %s, transfers failed (%s) and reverse failed (%s)",
                             order_number, transfer_exc, reverse_exc)
                logger.exception(reverse_exc)

            # Raise an exception so that your client code can inform the user appropriately.
            raise RedemptionFailed()
        else:
            # All transfers completed ok
            return completed_transfers

As you can see, there is some careful handling of the scenario where not all
transfers can be executed.

If you using Oscar then ensure that you create an `OrderSource` instance for
every transfer (rather than aggregating them all into one).  This will provide
better audit information.  Here's some example code:


.. code-block:: python

    try:
        transfers = api.redeem(order_number, user, total_incl_tax)
    except Exception:
        # Inform user of failed payment
    else:
        for transfer in transfers:
            source_type, __ = SourceType.objects.get_or_create(name="Accounts")
            source = Source(
                source_type=source_type,
                amount_allocated=transfer.amount,
                amount_debited=transfer.amount,
                reference=transfer.reference)
            self.add_payment_source(source)


Core accounts and account types
-------------------------------

A post-syncdb signal will create the common structure for account types and
accounts.  Some names can be controlled with settings, as indicated in
parentheses.

- **Assets**

  - **Sales**

    - Redemptions (`ACCOUNTS_REDEMPTIONS_NAME`) - where money is
      transferred to when an account is used to pay for something.
    - Lapsed (`ACCOUNTS_LAPSED_NAME`) - where money is transferred to
      when an account expires.  This is done by the
      'close_expired_accounts' management command.  The name of this
      account can be set using the `ACCOUNTS_LAPSED_NAME`.

  - **Cash**

    - "Bank" (`ACCOUNTS_BANK_NAME`) - the source account for creating new
      accounts that are paid for by the customer (eg a giftcard).  This
      account will not have a credit limit and will normally have a
      negative balance as money is only transferred out.

  - **Unpaid** - This contains accounts that are used as sources for other
    accounts but aren't paid for by the customer.  For instance, you might
    allow admins to create new accounts in the dashboard.  An account of this
    type will be the source account for the initial transfer.

- **Liabilities**

  - **Deferred income** - This contains customer accounts/giftcards.  You may
    want to create additional account types within this type to categorise
    accounts.

Example transactions
--------------------

Consider the following accounts and account types:

- **Assets**
    - **Sales**
        - Redemptions
        - Lapsed
    - **Cash**
        - Bank
    - **Unpaid**
        - Merchant funded
- **Liabilities**
    - **Deferred income**

Note that all accounts start with a balance of 0 and the sum of all balances
will always be zero.

*A customer purchases a £50 giftcard*

- A new account is created of type 'Deferred income' with an end date - £50 is
  transferred from the Bank to this new account

*A customer pays for a £30 order using their £50 giftcard*

- £30 is transferred from the giftcard account to the redemptions account

*The customer's giftcard expires with £20 still on it*

- £20 is transferred from the giftcard account to the lapsed account

*The customer phones up to complain and a staff member creates a new giftcard
for £20*

- A new account is created of type 'Deferred income' - £20 is transferred from
  the "Merchant funded" account to this new account

Settings
--------

There are settings to control the naming and initial unpaid and deferred income
account types:

* `ACCOUNTS_MIN_INITIAL_VALUE` The minimum value that can be used to create an
  account (or for a top-up)

* `ACCOUNTS_MAX_INITIAL_VALUE` The maximum value that can be transferred to an
  account.

Contributing
------------

Fork repo, set-up virtualenv and run::

    make install

Run tests with::

    ./runtests.py