Taxes implementation ready to be merged

[Moo]

Hi,

I have not implemented working salex tax implementation for GetPaid.
It will work in both United States and Europe.

Below are notes. Updates notes txt available here for the future
readers:

https://getpaid.googlecode.com/svn/Products.PloneGetPaid/branches/miohtama-taxes/Products/PloneGetPaid/docs/taxes_and_prices.txt



Taxes and prices
----------------

Problem: Depending on the country sales taxes may be included in the
store prices or they
may be applied to the total on the checkout.

* In Scandinavia sales taxes are included in the consumer visible
prices

* In US sales taxes depend on the state and are applied on the
checkout

To support both behaviors GetPaid must be sales tax aware

* How store owner manages taxes internally: are they put in the price
data or should system calculate them afterwards

* How consumer sees the prices: does the price tag contain taxes or
not

getpaid.core.interfaces.IPriceValueAdjuster is an utility to tackle
this problem.
It provides methods

* To get tax and tax free prices

* To get user visible prices

* Extendable tax behavior: subclass and override this utility to have
custom tax algorithms

* Different taxes for different item categories: line item and content
item adapters can be used
to return item specific tax percent

Where should be used
--------------------

* When totals are queried: CartTotals, checkout

* When item prices are displayed: portlets, page templates

* When invoice or recipient is generated

Products.PloneGetPaid.price module contains documentation how to use
IPriceValueAdjuster.

Backward incompatible changes
-----------------------------

The following backward incompatible changes have been made:

* Querying ILineContainerTotals utility needs to have
IPriceValueAdjuster argument

* Remove of getpaid.core.tax.TaxUtility

Code migration examples are available in Products.PloneGetPaid.price
module.

Necessary changes have been made to most of the parts of PloneGetPaid
and getpaid.core.
Some use cases might have slipped under the radar.

This work deals with sales tax only. getpaid.core support multiple tax
bases somehow.
getpaid.core.tax.TaxUtility and getpaid.core.interfaces.ITaxUtility
have been
removed, since they had no working implementations. getpaid.core.cart
uses now IPriceValueAdjuster directly. If one wants to support various
taxes
with getpaid.core it would need serious changes to user interface and
GetPaid subsystems
in any case.

Discussion
----------

The serious problem is that getpaid.core.order.Order class exposes
getTotal()
by directly inhering from CartItemTotals. It should not do this.

* When using getTotals() etc. functionality the site context is
available and
you cannot access such values as the current tax settings

* Currently you need to resort zope.app.component.hooks.getSite hack
to
have context inside tese functions.

I suggest deprecating getTotals() and CartItemTotals totally.
They should be replaced with site-aware adapters which can access
context data.

Also, when the order is create at least the following data
should be copied to the order to make orders future proof

* Used taxes

* Item price as taxed, tax free and taxes applied to item

Work available
--------------

2009/11: Available in getpaid.core and Products.PloneGetPaid miohtama-
taxes branch.
Branch is based on brandon-no-overrides branch.

Files touched

* getpaid.core.interfaces

* getpaid.core.cart

* Products.PloneGetPaid.interfaces

* Products.PloneGetPaid.price

* Products.PloneGetPaid.tests.base

* Products.PloneGetPaid.tests.test_taxes_and_prices

* Products.PloneGetPaid.browser.cart

*

[Christopher Johnson]

Hi Mikko,

Thanks for the notes and the work on getting taxes working!

I just wanted to get clarification on your email. The subject said the work was ready to merge, but the text said you have not implemented taxes. It looks from your notes that it is ready, so I just wanted to clarify.

With what you have done, how does someone create a new tax configuration (ie for another country, or for a state within a country)?

Thanks again,

Chris

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