File: docs/concepts/tax-direction-determination.concept.md

Concept: Tax Direction Determination

1. Overview

The system must determine the correct accounting direction for tax transactions (e.g., Tax Payable vs. Tax Receivable) based on the context of a voucher. This logic is inspired by the rules in Microsoft Dynamics 365 F&O and is encapsulated in the TaxDirectionDeterminationService.

The determination depends primarily on the "dominant" account type within the voucher (Vendor, Customer, or Ledger) and whether the applied TaxCode is marked as exempt.

2. Determination Flowchart

The following diagram illustrates the simplified decision-making process.

4. Posting Resolution Logic

Once the TaxDirection is determined, the TaxPostingResolverService is used to determine the final accounting entry. This service centralizes the rules for how tax is posted to the General Ledger.

The logic is as follows:

1. Determine Reporting Sign: The service first calculates the sign of the "Actual sales tax amount" as it would appear in reports.

   Journal Line Amount	Sales Tax Direction	Actual Sales Tax Amount Sign
   Positive (Debit)	Sales Tax Receivable	Positive
   Positive (Debit)	Sales Tax Payable	Negative
   Negative (Credit)	Sales Tax Receivable	Negative
   Negative (Credit)	Sales Tax Payable	Positive

2. Determine GL Account and Voucher Entry: Based on the direction and the calculated sign, the service determines the final debit/credit entry.

   Sales Tax Direction	Actual Sales Tax Amount Sign	Sales Tax Account Used	Amount on Voucher
   Sales Tax Receivable	Positive	TaxPostingGroup.TaxReceivableLedgerAccountId	Positive (Debit)
   Sales Tax Receivable	Negative	TaxPostingGroup.TaxReceivableLedgerAccountId	Negative (Credit)
   Sales Tax Payable	Positive	TaxPostingGroup.TaxPayableLedgerAccountId	Negative (Credit)
   Sales Tax Payable	Negative	TaxPostingGroup.TaxPayableLedgerAccountId	Positive (Debit)