update cost of sale_line depending on purchase state

__init__.py

@@ -7,5 +7,6 @@ from .sale import *
 def register():
     Pool.register(
         SaleLine,
+        Purchase,
         PurchaseLine,
         module='sale_opportunity_purchase_relation_margin', type_='model')

sale.py

@@ -1,54 +1,119 @@
-#The COPYRIGHT file at the top level of this repository contains
-#the full copyright notices and license terms.
-from trytond.model import fields
-from trytond.pool import Pool, PoolMeta
+# The COPYRIGHT file at the top level of this repository contains the full
+# copyright notices and license terms.
+from decimal import Decimal
 
-__all__ = ['SaleLine', 'PurchaseLine']
+from trytond.config import config
+from trytond.pool import Pool, PoolMeta
+DIGITS = int(config.get('digits', 'unit_price_digits', 4))
+
+__all__ = ['SaleLine', 'Purchase', 'PurchaseLine']
 __metaclass__ = PoolMeta
 
+_QUANTIZE = Decimal(str(10 ** -DIGITS))
+_CONFIRMED_STATES = ('confirmed', 'processing', 'done')
+
 
 class SaleLine:
     __name__ = 'sale.line'
 
-    @fields.depends('purchase_lines')
-    def on_change_purchase_lines(self):
-        changes = {}
-        if self.purchase_lines:
-            changes['cost_price'] = self.purchase_lines[0].unit_price
-        return changes
+    @classmethod
+    def update_cost_price(cls, lines):
+        pool = Pool()
+        Sale = pool.get('sale.sale')
+
+        to_write = []
+        sales = set()
+        for line in lines:
+            new_cost_price = line.calc_cost_price_from_purchase_lines()
+            if new_cost_price != line.cost_price:
+                to_write.extend(([line], {
+                            'cost_price': new_cost_price,
+                            }))
+                if line.sale.state not in ('draft', 'quotation'):
+                    sales.add(line.sale)
+
+        if to_write:
+            cls.write(*to_write)
+
+        # Ensure that the margin cache is valid
+        if sales:
+            sales = list(sales)
+            Sale.write(sales, {'margin_cache': None})
+            Sale.store_cache(sales)
+
+    def calc_cost_price_from_purchase_lines(self):
+        if not self.purchase_lines:
+            return self.product.cost_price
+
+        confirmed_purchase_lines = any(l.purchase.state in _CONFIRMED_STATES
+            for l in self.purchase_lines)
+        cost_price = Decimal('0.0')
+        quantity = 0
+        for purchase_line in self.purchase_lines:
+            if purchase_line.purchase.state == 'cancel':
+                continue
+            if (not confirmed_purchase_lines
+                    or purchase_line.purchase.state in _CONFIRMED_STATES):
+                cost_price += purchase_line.amount
+                quantity += purchase_line.quantity
+        if quantity:
+            return (cost_price / Decimal(str(quantity))).quantize(_QUANTIZE)
+        return self.product.cost_price
+
+
+class Purchase:
+    __name__ = 'purchase.purchase'
+
+    @classmethod
+    def cancel(cls, purchases):
+        super(Purchase, cls).cancel(purchases)
+        PurchaseLine.update_sale_lines_cost_price([l for p in purchases
+                for l in p.lines])
+
+    @classmethod
+    def draft(cls, purchases):
+        super(Purchase, cls).draft(purchases)
+        PurchaseLine.update_sale_lines_cost_price([l for p in purchases
+                for l in p.lines])
+
+    @classmethod
+    def confirm(cls, purchases):
+        super(Purchase, cls).confirm(purchases)
+        PurchaseLine.update_sale_lines_cost_price([l for p in purchases
+                for l in p.lines])
 
 
 class PurchaseLine:
     __name__ = 'purchase.line'
 
+    @classmethod
+    def create(cls, vlist):
+        purchase_lines = super(PurchaseLine, cls).create(vlist)
+        cls.update_sale_lines_cost_price(purchase_lines)
+        return purchase_lines
+
     @classmethod
     def write(cls, *args):
+        actions = iter(args)
+        modified_lines = []
+        for lines, values in zip(actions, actions):
+            if 'unit_price' in values or 'sale_lines' in values:
+                modified_lines.extend(lines)
+
+        super(PurchaseLine, cls).write(*args)
+
+        cls.update_sale_lines_cost_price(modified_lines)
+
+    @classmethod
+    def update_sale_lines_cost_price(cls, lines):
         pool = Pool()
         SaleLine = pool.get('sale.line')
-        Sale = pool.get('sale.sale')
-        actions = iter(args)
-        to_check = []
-        for lines, values in zip(actions, actions):
-            if 'unit_price' in values:
-                to_check.extend(lines)
-        super(PurchaseLine, cls).write(*args)
-        to_write = []
-        lines = SaleLine.search([
-                ('purchase_lines', 'in', [l.id for l in to_check]),
+
+        if not lines:
+            return
+
+        sale_lines = SaleLine.search([
+                ('purchase_lines', 'in', [l.id for l in lines]),
                 ])
-        sales = set()
-        for line in lines:
-            if (line.purchase_lines and
-                    line.cost_price != line.purchase_lines[0].unit_price):
-                to_write.extend(([line], {
-                            'cost_price': line.purchase_lines[0].unit_price,
-                            }))
-                if line.sale.state not in ('draft', 'quotation'):
-                    sales.add(line.sale)
-        if to_write:
-            SaleLine.write(*to_write)
-        # Ensure that the margin cache is valid
-        if sales:
-            sales = list(sales)
-            Sale.write(sales, {'margin_cache': None})
-            Sale.store_cache(sales)
+        if sale_lines:
+            SaleLine.update_cost_price(sale_lines)