Solidus VAT Roadmap

[mamhoff]

For now, this roadmap is work in Progress.

Solidus' VAT system has been very crazy, and I'm working slowly on reducing that crazyness. In the past weeks, I've been slowly moving parts of the taxation system into service objects, as well removing some duplicate and terse logic.

Much of the refactoring is done, from here on we're mostly looking at extracting logic into service objects and adding functionality for handling VAT pricing more elegantly.

Refactoring

• Add Zone#states and Zone#countries associations #529 (pull in some Spree work)
• Refactor zones #530 (Try simplifying zones)
• Improve taxation specs #650 (add real-life scenario specs for VAT and normal tax)
• Fix use of contains? in tax_rate.rb #657 (Use Zone#contains? rather than checking for zone equality)
• Simplify Spree::TaxRate#compute_amount #684 (Minor refactoring)
• Clean up tax rate match logic #705 (Clean up of very strange logic for rate selection)
• Use gross amount in return items #706 (Have ReturnItems use amount instead of pre_tax_amount, making the return items having to know much less about taxes)
• Add Zone.for_address scope #783 (Find zones by address, much faster than previous ways)
• Only check once whether we're in a non-default non-order zone #913 (Speed up application of calculcated tax adjustments)
• Use better i18n for generating tax adjustment labels #914 (Improve I18n for tax adjustment labels)
• Privatize TaxRate#default_zone_or_zone_match #915 (Make a method private, enabling Move the strange refunding logic from Spree::TaxRate into the default tax calculator #980)
• Move the strange refunding logic from Spree::TaxRate into the default tax calculator #980 (Contain bizarre logic in a calculator)
• Remove Line Item currency attribute #998 (Make all line items always have their order's currency)

Bugfixes

• Do not round pre-tax amounts #901 (Prevent rounding errors in some circumstances)
• Calculate pre tax amounts on the fly #941 (Really prevent those errors forever)
• Have Spree::Product#prices return master prices #969 (Have Spree::Product#prices return all prices)

Introduce service objects

• Add a PORO for creating tax adjustments #685 (Move taxation into new POROs instead of `TaxRate.adjust')
• Add a configurable line item pricer class

Untangling of the "default zone"

• Make cart taxes configurable via Spree::Store object #933 (Relieve the default tax zone of cart taxation responsibilies, make cart behaviour store-dependent)
• Replace the default zone with a default tax location and find rates by address only (much faster, more reliable)

Necessary new features

• Add prices and price selection for different VAT countries
• Add an interface for administering the prices for different variants/countries/currencies
• Understandable documentation

[mamhoff]

@gmacdougall @jhawthorn Here's a list of open tax-related PRs, in order of which one to merge first for the least amount of friction:

Core taxation system

• Move the strange refunding logic from Spree::TaxRate into the default tax calculator #980 Move refunding logic into calculator
• Add Spree::ShippingRateTax model #904 Add Spree::ShippingRateTax

Pricing

• Conservative line item pricer #994 API for Line Item Pricers
• WIP Superseding historical prices #987 Historical prices

Drive-by refactorings

• Always set a line item's currency to order currency #1007 Never set a line item's currency in strange ways.

[bbuchalter]

This issue seems quite out of date. Perhaps it's time to give it a freshening up in light of our intention to add related guides (#1606)? I'd love for the guide to reference any further planned development.

[mamhoff]

I'll close this issue now as the refactoring in question is mostly done. The one point not tackled so far is time-aware tax rates, for which I'll create a new issue.