Deep dive: Account, Stock, Sale, Purchase — +800 LOC business logic

Account:
- Multi-currency: company_currency_id, amount_total_signed
- Lock dates on res.company (period, fiscal year, tax) + enforcement in action_post
- Recurring entries: account.move.recurring with action_generate (copy+advance)
- Tax groups: amount_type='group' computes child taxes with include_base_amount
- ComputeTaxes batch function, findTaxAccount helper

Stock:
- Lot/Serial tracking: enhanced stock.lot with expiration dates + qty compute
- Routes: stock.route model with product/category/warehouse selectable flags
- Rules: stock.rule model with pull/push/buy/manufacture actions + procure methods
- Returns: action_return on picking (swap locations, copy moves)
- Product tracking extension (none/lot/serial) + route_ids M2M

Sale:
- Pricelist: get_product_price with fixed/percentage/formula computation
- Margin: purchase_price, margin, margin_percent on line + order totals
- Down payments: action_create_down_payment (deposit invoice at X%)

Purchase:
- 3-way matching: action_create_bill now updates qty_invoiced on PO lines
- Purchase agreements: purchase.requisition + line with state machine

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

addons/sale/models/sale_order.go

@@ -748,6 +748,134 @@ func initSaleOrder() {
 		}
 		return pickingIDs, nil
 	})
+
+	// action_create_down_payment: Create a deposit invoice for a percentage of the SO total.
+	// Mirrors: odoo/addons/sale/wizard/sale_make_invoice_advance.py
+	m.RegisterMethod("action_create_down_payment", func(rs *orm.Recordset, args ...interface{}) (interface{}, error) {
+		env := rs.Env()
+		soID := rs.IDs()[0]
+		percentage := float64(10) // Default 10%
+		if len(args) > 0 {
+			if p, ok := args[0].(float64); ok {
+				percentage = p
+			}
+		}
+
+		var total float64
+		var partnerID, companyID, currencyID, journalID int64
+		var soName string
+		err := env.Tx().QueryRow(env.Ctx(),
+			`SELECT COALESCE(amount_total, 0), partner_id, company_id, currency_id,
+			        COALESCE(journal_id, 0), COALESCE(name, '')
+			 FROM sale_order WHERE id = $1`, soID,
+		).Scan(&total, &partnerID, &companyID, &currencyID, &journalID, &soName)
+		if err != nil {
+			return nil, fmt.Errorf("sale: read SO %d for down payment: %w", soID, err)
+		}
+
+		downAmount := total * percentage / 100
+
+		// Find sales journal if not set on SO
+		if journalID == 0 {
+			env.Tx().QueryRow(env.Ctx(),
+				`SELECT id FROM account_journal
+				 WHERE type = 'sale' AND active = true AND company_id = $1
+				 ORDER BY sequence, id LIMIT 1`, companyID,
+			).Scan(&journalID)
+		}
+		if journalID == 0 {
+			journalID = 1
+		}
+
+		// Create deposit invoice
+		invoiceRS := env.Model("account.move")
+		inv, err := invoiceRS.Create(orm.Values{
+			"move_type":      "out_invoice",
+			"partner_id":     partnerID,
+			"company_id":     companyID,
+			"currency_id":    currencyID,
+			"journal_id":     journalID,
+			"invoice_origin": soName,
+			"date":           time.Now().Format("2006-01-02"),
+		})
+		if err != nil {
+			return nil, fmt.Errorf("sale: create down payment invoice for SO %d: %w", soID, err)
+		}
+		moveID := inv.ID()
+
+		// Find revenue account
+		var revenueAccountID int64
+		env.Tx().QueryRow(env.Ctx(),
+			`SELECT id FROM account_account WHERE code = '8300' AND company_id = $1 LIMIT 1`,
+			companyID).Scan(&revenueAccountID)
+		if revenueAccountID == 0 {
+			env.Tx().QueryRow(env.Ctx(),
+				`SELECT id FROM account_account
+				 WHERE account_type LIKE 'income%%' AND company_id = $1
+				 ORDER BY code LIMIT 1`, companyID).Scan(&revenueAccountID)
+		}
+
+		// Find receivable account
+		var receivableAccountID int64
+		env.Tx().QueryRow(env.Ctx(),
+			`SELECT id FROM account_account
+			 WHERE account_type = 'asset_receivable' AND company_id = $1
+			 ORDER BY code LIMIT 1`, companyID).Scan(&receivableAccountID)
+		if receivableAccountID == 0 {
+			receivableAccountID = revenueAccountID
+		}
+
+		lineRS := env.Model("account.move.line")
+
+		// Down payment product line (credit)
+		_, err = lineRS.Create(orm.Values{
+			"move_id":      moveID,
+			"name":         fmt.Sprintf("Down payment of %.0f%%", percentage),
+			"quantity":     1.0,
+			"price_unit":   downAmount,
+			"account_id":   revenueAccountID,
+			"company_id":   companyID,
+			"journal_id":   journalID,
+			"currency_id":  currencyID,
+			"partner_id":   partnerID,
+			"display_type": "product",
+			"debit":        0.0,
+			"credit":       downAmount,
+			"balance":      -downAmount,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("sale: create down payment line: %w", err)
+		}
+
+		// Receivable line (debit)
+		_, err = lineRS.Create(orm.Values{
+			"move_id":                  moveID,
+			"name":                     "/",
+			"quantity":                 1.0,
+			"account_id":              receivableAccountID,
+			"company_id":              companyID,
+			"journal_id":              journalID,
+			"currency_id":             currencyID,
+			"partner_id":              partnerID,
+			"display_type":            "payment_term",
+			"debit":                   downAmount,
+			"credit":                  0.0,
+			"balance":                 downAmount,
+			"amount_residual":         downAmount,
+			"amount_residual_currency": downAmount,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("sale: create down payment receivable line: %w", err)
+		}
+
+		return map[string]interface{}{
+			"type":      "ir.actions.act_window",
+			"res_model": "account.move",
+			"res_id":    moveID,
+			"view_mode": "form",
+			"target":    "current",
+		}, nil
+	})
 }
 
 // initSaleOrderLine registers sale.order.line — individual line items on a sales order.