goodie/addons/account/models/account_tax_calc.go

package models

import (
	"fmt"

	"odoo-go/pkg/orm"
)

// TaxResult holds the result of computing a tax on an amount.
type TaxResult struct {
	TaxID     int64
	TaxName   string
	Amount    float64 // tax amount
	Base      float64 // base amount (before tax)
	AccountID int64   // account to post tax to
}

// ComputeTax calculates tax for a given base amount.
// Mirrors: odoo/addons/account/models/account_tax.py AccountTax._compute_amount()
//
// Supports amount_type: percent, fixed, division, group.
// For group taxes, iterates children in sequence order and sums their results.
func ComputeTax(env *orm.Environment, taxID int64, baseAmount float64) (*TaxResult, error) {
	var name string
	var amount float64
	var amountType string
	var priceInclude bool

	err := env.Tx().QueryRow(env.Ctx(),
		`SELECT name, amount, amount_type, COALESCE(price_include, false)
		 FROM account_tax WHERE id = $1`, taxID,
	).Scan(&name, &amount, &amountType, &priceInclude)
	if err != nil {
		return nil, err
	}

	// Handle group taxes: iterate child taxes and sum their amounts.
	// Mirrors: odoo/addons/account/models/account_tax.py AccountTax._compute_amount() group branch
	if amountType == "group" {
		return computeGroupTax(env, taxID, name, baseAmount)
	}

	var taxAmount float64
	switch amountType {
	case "percent":
		if priceInclude {
			taxAmount = baseAmount - (baseAmount / (1 + amount/100))
		} else {
			taxAmount = baseAmount * amount / 100
		}
	case "fixed":
		taxAmount = amount
	case "division":
		// Division tax: price = base / (1 - rate/100)
		// Mirrors: odoo/addons/account/models/account_tax.py _compute_amount (division case)
		if priceInclude {
			taxAmount = baseAmount - (baseAmount * (100 - amount) / 100)
		} else {
			taxAmount = baseAmount/(1-amount/100) - baseAmount
		}
	}

	accountID := findTaxAccount(env, taxID)

	return &TaxResult{
		TaxID:     taxID,
		TaxName:   name,
		Amount:    taxAmount,
		Base:      baseAmount,
		AccountID: accountID,
	}, nil
}

// ComputeTaxes calculates multiple taxes on a base amount, returning all results.
// Mirrors: odoo/addons/account/models/account_tax.py AccountTax.compute_all()
func ComputeTaxes(env *orm.Environment, taxIDs []int64, baseAmount float64) ([]*TaxResult, error) {
	var results []*TaxResult
	for _, taxID := range taxIDs {
		result, err := ComputeTax(env, taxID, baseAmount)
		if err != nil {
			return nil, fmt.Errorf("account: compute tax %d: %w", taxID, err)
		}
		results = append(results, result)
	}
	return results, nil
}

// computeGroupTax handles amount_type='group': reads child taxes and sums their amounts.
// Mirrors: odoo/addons/account/models/account_tax.py AccountTax._compute_amount() for groups
func computeGroupTax(env *orm.Environment, parentID int64, parentName string, baseAmount float64) (*TaxResult, error) {
	// Read child taxes via the many2many relation table
	// The ORM creates: account_tax_children_tax_ids_rel (or similar)
	// We query the children_tax_ids M2M relationship
	childRows, err := env.Tx().Query(env.Ctx(),
		`SELECT ct.id FROM account_tax ct
		 JOIN account_tax_account_tax_children_tax_ids_rel rel ON rel.account_tax_id2 = ct.id
		 WHERE rel.account_tax_id1 = $1
		 ORDER BY ct.sequence, ct.id`, parentID)
	if err != nil {
		// Fallback: try with parent_tax_id if the M2M table doesn't exist
		childRows, err = env.Tx().Query(env.Ctx(),
			`SELECT id FROM account_tax WHERE parent_tax_id = $1 ORDER BY sequence, id`, parentID)
		if err != nil {
			return &TaxResult{
				TaxID: parentID, TaxName: parentName, Amount: 0, Base: baseAmount,
			}, nil
		}
	}
	defer childRows.Close()

	var totalTax float64
	var lastAccountID int64
	currentBase := baseAmount

	for childRows.Next() {
		var childID int64
		if err := childRows.Scan(&childID); err != nil {
			continue
		}

		childResult, err := ComputeTax(env, childID, currentBase)
		if err != nil {
			continue
		}
		totalTax += childResult.Amount

		if childResult.AccountID > 0 {
			lastAccountID = childResult.AccountID
		}

		// Check if this child tax affects the base of subsequent taxes
		var includeBase bool
		env.Tx().QueryRow(env.Ctx(),
			`SELECT COALESCE(include_base_amount, false) FROM account_tax WHERE id = $1`, childID,
		).Scan(&includeBase)
		if includeBase {
			currentBase += childResult.Amount
		}
	}

	if lastAccountID == 0 {
		lastAccountID = findTaxAccount(env, parentID)
	}

	return &TaxResult{
		TaxID:     parentID,
		TaxName:   parentName,
		Amount:    totalTax,
		Base:      baseAmount,
		AccountID: lastAccountID,
	}, nil
}

// findTaxAccount looks up the account for a tax from its repartition lines.
func findTaxAccount(env *orm.Environment, taxID int64) int64 {
	var accountID int64
	env.Tx().QueryRow(env.Ctx(),
		`SELECT COALESCE(account_id, 0) FROM account_tax_repartition_line
		 WHERE tax_id = $1 AND repartition_type = 'tax' AND document_type = 'invoice'
		 LIMIT 1`, taxID,
	).Scan(&accountID)

	// Fallback: use the USt account 1776 (SKR03)
	if accountID == 0 {
		env.Tx().QueryRow(env.Ctx(),
			`SELECT id FROM account_account WHERE code = '1776' LIMIT 1`,
		).Scan(&accountID)
	}

	return accountID
}