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The gateway’s JSON, parsed in the business logic

A subscription service reaches into a payment provider’s JSON — txn_st_v3, ch_ident_key, resp_cd — and decides business outcomes from it. Put an adapter and a domain model between them so swapping provider is a new class, not a rewrite.

Intermediate20 min on the clock5 graded checks · 100 pointsCode Someone Else Can Change, in C#Pro

See alsoThe vendor’s field names, everywhereThe same boundary in JavaScript, without an interface to hang it on.

Graded by reading your code against the checklist below.

What you build

A PaymentResult domain record
An IGatewayResponseAdapter interface
A VendorPaymentAdapter that does all the parsing
SubscriptionManager depends on the interface, not the vendor
No JSON and no vendor key anywhere in SubscriptionManager

Done means

A second provider is a second adapter, and no existing business code changes.

How it is graded

Published in full, before you start — every point is one of these and there is nothing else.

A domain record carries the outcome+20Enforcing the rules of your data
The seam is an interface in the domain+20Where code lives
All parsing happens in the adapter+30Where code lives
The manager depends on the seam, not the vendor+20Where code lives
What "succeeded" means is decided once+10Where code lives

What it teaches

Enforcing the rules of your dataintermediate

A cart that can hold the same product twice, or a quantity that can go to zero, is a bug you will chase through the UI forever — the rules belong in the data layer.

Where code livesintermediate

A vertical slice keeps one feature — its endpoint, its validation, its data access — in one folder, so changing checkout means opening one place instead of four layers.

The rest of Code Someone Else Can Change, in C#

Five levels deep, and the transfer is at the bottomBeginner · 15 min