[IMP] - Create contract on sale order confirmation

- On Sale Order confirmation, a contract is created for each contract template used on sale order lines
- A not finished contract can be mentioned on sale order line
- A sale order line linked to a contract will update it and don't create a new one if it had the same template

product_contract/views/sale_order.xml

@@ -12,9 +12,27 @@
         <field name="model">sale.order</field>
         <field name="inherit_id" ref="sale.view_order_form"/>
         <field name="arch" type="xml">
+            <xpath expr="//div[@name='button_box']" position="inside">
+                <button name="action_show_contracts"
+                        type="object" icon="fa-book"
+                        class="oe_stat_button"
+                        attrs="{'invisible': ['|', ('is_contract', '!=', True), ('state', 'not in', ['sale', 'done'])]}">
+                    <field string="Contracts"
+                           name="contract_count"
+                           widget="statinfo"/>
+                </button>
+            </xpath>
             <xpath expr="//field[@name='order_line']" position="before">
                 <field name="is_contract" invisible="1"/>
             </xpath>
+             <xpath expr="//field[@name='order_line']/form//field[@name='product_id']"
+                   position="after">
+                 <field name="contract_template_id" invisible="1"/>
+                 <field name="contract_id"
+                        attrs="{'invisible': [('is_contract', '=', False)]}"
+                        domain="[('partner_id','=',parent.partner_id),('contract_template_id','=',contract_template_id)]"
+                 />
+             </xpath>
             <xpath expr="//field[@name='order_line']/form//field[@name='tax_id']/parent::group"
                    position="after">
                 <separator colspan="4" string="Recurrence Invoicing"