Billing integration for Agresso Unit 4

We need to develop an application that generates legal billing lines for the Agresso Unit4 system. The business operates as a wholesale telecom provider, and the source of truth for active customer connections resides in a separate system.

The goal is to create an app that produces billing lines based on a user-configurable setup. The configuration should be flexible, allowing users to adjust pricing and rule parameters as needed.

The app should output documents that can be imported into Agresso Unit4, ensuring the billing lines comply with Icelandic legal and regulatory requirements.

On-Demand Processing Flow

Collect inputs from Tengi

For each customer, product, connection, and billing period, read summarized usage data from sot_usage_snapshots.

Load merged pricing configuration

Combine pricing_rules (base configuration) with any customer-specific contract_pricing_overrides.

Apply pricing logic

Evaluate the applicable pricing model (flat, tiered, or per_unit).

Apply proration, discounts, and surcharges as defined.

Apply tax calculations

Look up tax_rates based on the customer’s tax_profile_id.

Generate idempotent billing lines

Compute a unique source_event_hash from key fields
(customer_id, contract_id, product_code, connection_id, period_start, period_end, qty, and pricing config version).

Upsert billing lines using source_event_hash to prevent duplicates.

Emit reconciliation report

Generate a summary with counts, totals, and exceptions for validation and auditing.

• An app that can be run against our custom system (specifications on that will be shared later)
• Needs to be tested , both unit and integration tests