subscription/addon/diff/README.md

Subscription Addon Diff Package

This package implements functionality to apply and restore subscription addons to subscription specifications.

Core Components

Diffable Interface (diff.go)

The central interface for objects that can be both applied to and removed from a subscription specification:

• GetApplies(): Returns operations that will be applied to the specification
• GetRestores(): Returns operations that will be applied to revert changes

Addon Operations (addon.go)

Handles the conversion of subscription addons into diffable objects that can modify subscription specifications:

• GetDiffableFromAddon(): Creates a diffable object from a subscription addon
• diffable: Wrapper for apply and restore implementations for a single SubscriptionAddonInstance

Application Logic (apply.go)

Algorithm for applying subscription addon rate cards to subscription specifications. A specification for it is as follows:

1. Given a SubscriptionAddon, SubscriptionAddonInstances can be created.
2. Given a SubscriptionAddonInstance and a SubscriptionView, the SubscriptionAddonRateCards can be matched to the SubscriptionView's items.

Then, for each SubscriptionAddonRateCard:

• During the Addon's entire cadence, the RateCard has to be present: either as a modification on an existing item, or as a new item.
• The RateCard's contents should always be effective SubscriptionAddonInstnce.Quantity times: if quantity is 0, the RateCard should not be present.

The merging logic of two RateCards is defined in the subscriptionaddon package, not here.

If the above are met for each SubscriptionAddonRateCard of each SubscriptionAddonInstance, then the SubscriptionAddon has been applied to the SubscriptionSpec.

Usage

This package is meant to be internal to subscription.