[FIX] l10n_be_intrastat: manage dropshipping triangular

Before this commit, the triangular case was not handled:
A transaction in dropshipping which happens outside our country
(provider and customer both outside our country)
was counted in the intrastat XML when it shouldn't

After this commit, those transaction are not accounted for in the XML

opw-800342

addons/l10n_be_intrastat/wizard/xml_decl.py

@@ -164,6 +164,7 @@ class XmlDeclaration(models.TransientModel):
         lines = self.env.cr.fetchall()
         invoicelines_ids = [rec[0] for rec in lines]
         invoicelines = self.env['account.invoice.line'].browse(invoicelines_ids)
+
         for inv_line in invoicelines:
 
             #Check type of transaction
@@ -189,6 +190,8 @@ class XmlDeclaration(models.TransientModel):
                 #comes from purchase
                 po_lines = self.env['purchase.order.line'].search([('invoice_lines', 'in', inv_line.id)], limit=1)
                 if po_lines:
+                    if self._is_situation_triangular(company, po_line=po_lines):
+                        continue
                     location = self.env['stock.location'].browse(po_lines.order_id._get_destination_location())
                     region_id = self.env['stock.warehouse'].get_regionid_from_locationid(location)
                     if region_id:
@@ -197,6 +200,8 @@ class XmlDeclaration(models.TransientModel):
                 #comes from sales
                 so_lines = self.env['sale.order.line'].search([('invoice_lines', 'in', inv_line.id)], limit=1)
                 if so_lines:
+                    if self._is_situation_triangular(company, so_line=so_lines):
+                        continue
                     saleorder = so_lines.order_id
                     if saleorder and saleorder.warehouse_id and saleorder.warehouse_id.region_id:
                         exreg = IntrastatRegion.browse(saleorder.warehouse_id.region_id.id).code
@@ -286,3 +291,24 @@ class XmlDeclaration(models.TransientModel):
         dim = ET.SubElement(item, 'Dim')
         dim.set('prop', prop)
         dim.text = value
+
+    def _is_situation_triangular(self, company, po_line=False, so_line=False):
+        # Ignoring what is purchased and sold by us with a dropshipping route
+        # outside of our country, or completely within it
+        # https://www.nbb.be/doc/dq/f_pdf_ex/intra2017fr.pdf (§ 4.x)
+        dropship_pick_type = self.env.ref('stock_dropshipping.picking_type_dropship', raise_if_not_found=False)
+        if not dropship_pick_type:
+            return False
+        stock_move_domain = [('picking_type_id', '=', dropship_pick_type.id)]
+
+        if po_line:
+            stock_move_domain.append(('purchase_line_id', '=', po_line.id))
+        if so_line:
+            stock_move_domain.append(('procurement_id.sale_line_id', '=', so_line.id))
+
+        stock_move = self.env['stock.move'].search(stock_move_domain, limit=1)
+        return stock_move and (
+            (stock_move.partner_id.country_id.code != company.country_id.code and
+                stock_move.picking_partner_id.country_id.code != company.country_id.code) or
+            (stock_move.partner_id.country_id.code == company.country_id.code and
+                stock_move.picking_partner_id.country_id.code == company.country_id.code))