diff --git a/CHANGELOG b/CHANGELOG
index 1c568faf95..83a505a92d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,5 @@
+* Add configured delay for processing purchase
+* Allow to reset to draft confirmed but not processed purchase
 * Show number and reference in purchase rec_name
 * Remove support for Python 2.7
 * Invoice purchased product instead of received product
diff --git a/configuration.py b/configuration.py
index d20d618cb9..aaa3ac5221 100644
--- a/configuration.py
+++ b/configuration.py
@@ -37,6 +37,10 @@ class Configuration(
                 ]))
     purchase_invoice_method = fields.MultiValue(purchase_invoice_method)
     get_purchase_invoice_method = get_purchase_methods('invoice_method')
+    purchase_process_after = fields.TimeDelta("Process Purchase after",
+        help="The grace period during which confirmed purchase "
+        "can still be reset to draft.\n"
+        "Applied only if a worker queue is activated.")
 
     @classmethod
     def multivalue_model(cls, field):
diff --git a/invoice.py b/invoice.py
index a95d0d9f59..53eb3a59e2 100644
--- a/invoice.py
+++ b/invoice.py
@@ -18,11 +18,11 @@ def process_purchase(func):
         pool = Pool()
         Purchase = pool.get('purchase.purchase')
         with Transaction().set_context(_check_access=False):
-            purchases = Purchase.browse(
-                set(p for i in cls.browse(invoices) for p in i.purchases))
+            purchases = set(
+                p for i in cls.browse(invoices) for p in i.purchases)
         func(cls, invoices)
-        with Transaction().set_context(_check_access=False):
-            Purchase.process(purchases)
+        if purchases:
+            Purchase.__queue__.process(purchases)
     return wrapper
 
 
@@ -155,11 +155,9 @@ class InvoiceLine(metaclass=PoolMeta):
         pool = Pool()
         Purchase = pool.get('purchase.purchase')
         with Transaction().set_context(_check_access=False):
-            lines = cls.browse(lines)
-            invoices = (l.invoice for l in lines
+            invoices = (l.invoice for l in cls.browse(lines)
                 if l.type == 'line' and l.invoice)
-            purchases = Purchase.browse(
-                set(p for i in invoices for p in i.purchases))
+            purchases = set(p for i in invoices for p in i.purchases)
         super(InvoiceLine, cls).delete(lines)
-        with Transaction().set_context(_check_access=False):
-            Purchase.process(purchases)
+        if purchases:
+            Purchase.__queue__.process(purchases)
diff --git a/purchase.py b/purchase.py
index 824dce7056..3e3151dac6 100644
--- a/purchase.py
+++ b/purchase.py
@@ -208,6 +208,7 @@ class Purchase(Workflow, ModelSQL, ModelView, TaxableMixin):
                 ('draft', 'quotation'),
                 ('quotation', 'confirmed'),
                 ('confirmed', 'processing'),
+                ('confirmed', 'draft'),
                 ('processing', 'processing'),
                 ('processing', 'done'),
                 ('done', 'processing'),
@@ -222,7 +223,8 @@ class Purchase(Workflow, ModelSQL, ModelView, TaxableMixin):
                     'depends': ['state'],
                     },
                 'draft': {
-                    'invisible': ~Eval('state').in_(['cancel', 'quotation']),
+                    'invisible': ~Eval('state').in_(
+                        ['cancel', 'quotation', 'confirmed']),
                     'icon': If(Eval('state') == 'cancel', 'tryton-clear',
                         'tryton-go-previous'),
                     'depends': ['state'],
@@ -850,8 +852,15 @@ class Purchase(Workflow, ModelSQL, ModelView, TaxableMixin):
     @ModelView.button
     @Workflow.transition('confirmed')
     def confirm(cls, purchases):
+        pool = Pool()
+        Configuration = pool.get('purchase.configuration')
         cls.set_purchase_date(purchases)
         cls.store_cache(purchases)
+        config = Configuration(1)
+        with Transaction().set_context(
+                queue_name='purchase',
+                queue_scheduled_at=config.purchase_process_after):
+            cls.__queue__.process(purchases)
 
     @classmethod
     @Workflow.transition('processing')
@@ -873,13 +882,6 @@ class Purchase(Workflow, ModelSQL, ModelView, TaxableMixin):
     def handle_shipment_exception(cls, purchases):
         pass
 
-    @classmethod
-    def cron_process(cls):
-        purchases = cls.search([
-                ('state', '=', 'confirmed'),
-                ])
-        cls.process(purchases)
-
     @classmethod
     @ModelView.button
     def process(cls, purchases):
@@ -1740,7 +1742,7 @@ class HandleShipmentException(Wizard):
                 'moves_recreated': [('add', moves_recreated)],
                 })
 
-        Purchase.process([purchase])
+        Purchase.__queue__.process([purchase])
         return 'end'
 
 
@@ -1801,7 +1803,7 @@ class HandleInvoiceException(Wizard):
             'invoices_recreated': [('add', invoices_recreated)],
             })
 
-        Purchase.process([purchase])
+        Purchase.__queue__.process([purchase])
         return 'end'
 
 
diff --git a/purchase.xml b/purchase.xml
index 3cacb5cd86..08b5762339 100644
--- a/purchase.xml
+++ b/purchase.xml
@@ -361,29 +361,6 @@ this repository contains the full copyright notices and license terms. -->
             <field name="action" ref="report_purchase"/>
         </record>
 
-        <record model="res.user" id="user_process_purchase">
-            <field name="login">user_cron_process_purchase</field>
-            <field name="name">Cron Process Purchase</field>
-            <field name="signature"></field>
-            <field name="active" eval="False"/>
-        </record>
-        <record model="res.user-res.group"
-            id="user_process_purchase_group_purchase">
-            <field name="user" ref="user_process_purchase"/>
-            <field name="group" ref="group_purchase"/>
-        </record>
-
-        <record model="ir.cron" id="cron_process_purchase">
-            <field name="name">Process Confirmed Purchases</field>
-            <field name="request_user" ref="res.user_admin"/>
-            <field name="user" ref="user_process_purchase"/>
-            <field name="interval_number" eval="1"/>
-            <field name="interval_type">hours</field>
-            <field name="repeat_missed" eval="False"/>
-            <field name="model">purchase.purchase</field>
-            <field name="function">cron_process</field>
-        </record>
-
         <record model="ir.ui.view" id="purchase_line_view_form">
             <field name="model">purchase.line</field>
             <field name="type">form</field>
diff --git a/stock.py b/stock.py
index fdff0f13b8..90e2f80423 100644
--- a/stock.py
+++ b/stock.py
@@ -1,5 +1,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+from functools import wraps
+
 from sql import Null
 from sql.aggregate import Max
 from sql.operators import Concat
@@ -14,6 +16,22 @@ from trytond.modules.product import price_digits
 __all__ = ['ShipmentIn', 'ShipmentInReturn', 'Move', 'Location']
 
 
+def process_purchase(moves_field):
+    def _process_purchase(func):
+        @wraps(func)
+        def wrapper(cls, shipments):
+            pool = Pool()
+            Purchase = pool.get('purchase.purchase')
+            with Transaction().set_context(_check_access=False):
+                purchases = set(m.purchase for s in cls.browse(shipments)
+                    for m in getattr(s, moves_field) if m.purchase)
+            func(cls, shipments)
+            if purchases:
+                Purchase.__queue__.process(purchases)
+        return wrapper
+    return _process_purchase
+
+
 class ShipmentIn(metaclass=PoolMeta):
     __name__ = 'stock.shipment.in'
 
@@ -38,35 +56,6 @@ class ShipmentIn(metaclass=PoolMeta):
                     'it was generated by a purchase.'),
                 })
 
-    @classmethod
-    def write(cls, *args):
-        pool = Pool()
-        Purchase = pool.get('purchase.purchase')
-        PurchaseLine = pool.get('purchase.line')
-
-        super(ShipmentIn, cls).write(*args)
-
-        actions = iter(args)
-        for shipments, values in zip(actions, actions):
-            if values.get('state') not in ('received', 'cancel'):
-                continue
-            purchases = []
-            move_ids = []
-            for shipment in shipments:
-                move_ids.extend([x.id for x in shipment.incoming_moves])
-
-            purchase_lines = PurchaseLine.search([
-                    ('moves', 'in', move_ids),
-                    ])
-            if purchase_lines:
-                for purchase_line in purchase_lines:
-                    if purchase_line.purchase not in purchases:
-                        purchases.append(purchase_line.purchase)
-
-            with Transaction().set_context(_check_access=False):
-                purchases = Purchase.browse([p.id for p in purchases])
-                Purchase.process(purchases)
-
     @classmethod
     @ModelView.button
     @Workflow.transition('draft')
@@ -80,6 +69,20 @@ class ShipmentIn(metaclass=PoolMeta):
 
         return super(ShipmentIn, cls).draft(shipments)
 
+    @classmethod
+    @ModelView.button
+    @Workflow.transition('received')
+    @process_purchase('incoming_moves')
+    def receive(cls, shipments):
+        super(ShipmentIn, cls).receive(shipments)
+
+    @classmethod
+    @ModelView.button
+    @Workflow.transition('cancel')
+    @process_purchase('incoming_moves')
+    def cancel(cls, shipments):
+        super(ShipmentIn, cls).cancel(shipments)
+
 
 class ShipmentInReturn(metaclass=PoolMeta):
     __name__ = 'stock.shipment.in.return'
@@ -121,34 +124,6 @@ class ShipmentInReturn(metaclass=PoolMeta):
                     values=[value]))
         super(ShipmentInReturn, cls).__register__(module_name)
 
-    @classmethod
-    def write(cls, *args):
-        pool = Pool()
-        Purchase = pool.get('purchase.purchase')
-        PurchaseLine = pool.get('purchase.line')
-
-        super(ShipmentInReturn, cls).write(*args)
-
-        actions = iter(args)
-        for shipments, values in zip(actions, actions):
-            if values.get('state') != 'done':
-                continue
-            move_ids = []
-            for shipment in shipments:
-                move_ids.extend([x.id for x in shipment.moves])
-
-            purchase_lines = PurchaseLine.search([
-                    ('moves', 'in', move_ids),
-                    ])
-            purchases = set()
-            if purchase_lines:
-                for purchase_line in purchase_lines:
-                    purchases.add(purchase_line.purchase)
-
-            with Transaction().set_context(_check_access=False):
-                purchases = Purchase.browse([p.id for p in purchases])
-                Purchase.process(purchases)
-
     @classmethod
     @ModelView.button
     @Workflow.transition('draft')
@@ -162,6 +137,27 @@ class ShipmentInReturn(metaclass=PoolMeta):
 
         return super(ShipmentInReturn, cls).draft(shipments)
 
+    @classmethod
+    @ModelView.button
+    @Workflow.transition('done')
+    @process_purchase('moves')
+    def done(cls, shipments):
+        super(ShipmentInReturn, cls).done(shipments)
+
+
+def process_purchase_move(func):
+    @wraps(func)
+    def wrapper(cls, moves):
+        pool = Pool()
+        Purchase = pool.get('purchase.purchase')
+        with Transaction().set_context(_check_access=False):
+            purchases = set(
+                m.purchase for m in cls.browse(moves) if m.purchase)
+        func(cls, moves)
+        if purchases:
+            Purchase.__queue__.process(purchases)
+    return wrapper
+
 
 class Move(metaclass=PoolMeta):
     __name__ = 'stock.move'
@@ -314,41 +310,15 @@ class Move(metaclass=PoolMeta):
     @classmethod
     @ModelView.button
     @Workflow.transition('cancel')
+    @process_purchase_move
     def cancel(cls, moves):
-        pool = Pool()
-        Purchase = pool.get('purchase.purchase')
-        PurchaseLine = pool.get('purchase.line')
-
         super(Move, cls).cancel(moves)
-        purchase_lines = PurchaseLine.search([
-                ('moves', 'in', [m.id for m in moves]),
-                ])
-        if purchase_lines:
-            purchase_ids = list(set(l.purchase.id for l in purchase_lines))
-            purchases = Purchase.browse(purchase_ids)
-            Purchase.process(purchases)
 
     @classmethod
+    @process_purchase_move
     def delete(cls, moves):
-        pool = Pool()
-        Purchase = pool.get('purchase.purchase')
-        PurchaseLine = pool.get('purchase.line')
-
-        purchases = set()
-        purchase_lines = PurchaseLine.search([
-                ('moves', 'in', [m.id for m in moves]),
-                ])
-
         super(Move, cls).delete(moves)
 
-        if purchase_lines:
-            for purchase_line in purchase_lines:
-                purchases.add(purchase_line.purchase)
-            if purchases:
-                with Transaction().set_context(_check_access=False):
-                    purchases = Purchase.browse([p.id for p in purchases])
-                    Purchase.process(purchases)
-
 
 class Location(metaclass=PoolMeta):
     __name__ = 'stock.location'
diff --git a/tests/scenario_purchase.rst b/tests/scenario_purchase.rst
index 197a742f35..598702f07c 100644
--- a/tests/scenario_purchase.rst
+++ b/tests/scenario_purchase.rst
@@ -153,9 +153,6 @@ Purchase 5 products::
     >>> purchase.click('confirm')
     >>> purchase.untaxed_amount, purchase.tax_amount, purchase.total_amount
     (Decimal('25.00'), Decimal('2.50'), Decimal('27.50'))
-    >>> purchase.click('process')
-    >>> purchase.untaxed_amount, purchase.tax_amount, purchase.total_amount
-    (Decimal('25.00'), Decimal('2.50'), Decimal('27.50'))
     >>> purchase.state
     'processing'
     >>> purchase.shipment_state
@@ -215,7 +212,6 @@ Purchase 5 products with an invoice method 'on shipment'::
     >>> purchase_line.quantity = 3.0
     >>> purchase.click('quote')
     >>> purchase.click('confirm')
-    >>> purchase.click('process')
     >>> purchase.state
     'processing'
     >>> purchase.shipment_state
@@ -309,7 +305,6 @@ Create a Return::
     >>> return_line.description = 'Comment'
     >>> return_.click('quote')
     >>> return_.click('confirm')
-    >>> return_.click('process')
     >>> return_.state
     'processing'
     >>> return_.shipment_state
@@ -376,7 +371,6 @@ Mixing return and purchase::
     >>> mixline2.quantity = -2.
     >>> mix.click('quote')
     >>> mix.click('confirm')
-    >>> mix.click('process')
     >>> mix.state
     'processing'
     >>> mix.shipment_state
@@ -445,7 +439,6 @@ Mixing stuff with an invoice method 'on shipment'::
     >>> mixline2.quantity = -3.
     >>> mix.click('quote')
     >>> mix.click('confirm')
-    >>> mix.click('process')
     >>> mix.state
     'processing'
     >>> mix.shipment_state
@@ -492,7 +485,6 @@ Purchase services::
     >>> service_purchase.save()
     >>> service_purchase.click('quote')
     >>> service_purchase.click('confirm')
-    >>> service_purchase.click('process')
     >>> service_purchase.state
     'processing'
     >>> service_purchase.shipment_state
@@ -535,7 +527,6 @@ linked to invoices::
     >>> line.quantity = 10.0
     >>> purchase.click('quote')
     >>> purchase.click('confirm')
-    >>> purchase.click('process')
     >>> shipment = ShipmentIn()
     >>> shipment.supplier = supplier
     >>> for move in purchase.moves:
@@ -570,7 +561,6 @@ correctly linked to invoices::
     >>> line.quantity = 10.0
     >>> purchase.click('quote')
     >>> purchase.click('confirm')
-    >>> purchase.click('process')
     >>> shipment = ShipmentIn()
     >>> shipment.supplier = supplier
     >>> for move in purchase.moves:
@@ -607,7 +597,6 @@ Deleting a line from a invoice should recreate it::
     >>> line.quantity = 10.0
     >>> purchase.click('quote')
     >>> purchase.click('confirm')
-    >>> purchase.click('process')
     >>> invoice, = purchase.invoices
     >>> invoice_line, = invoice.lines
     >>> invoice.lines.remove(invoice_line)
diff --git a/tests/scenario_purchase_empty.rst b/tests/scenario_purchase_empty.rst
index 44345a2582..95392450d9 100644
--- a/tests/scenario_purchase_empty.rst
+++ b/tests/scenario_purchase_empty.rst
@@ -46,9 +46,6 @@ Create empty purchase::
     Decimal('0')
     >>> purchase.click('confirm')
     >>> purchase.state
-    'confirmed'
-    >>> purchase.click('process')
-    >>> purchase.state
     'done'
     >>> purchase.shipment_state
     'none'
diff --git a/view/configuration_form.xml b/view/configuration_form.xml
index c430726536..2871ee1c37 100644
--- a/view/configuration_form.xml
+++ b/view/configuration_form.xml
@@ -6,4 +6,7 @@ this repository contains the full copyright notices and license terms. -->
     <field name="purchase_sequence"/>
     <label name="purchase_invoice_method" />
     <field name="purchase_invoice_method" />
+    <newline/>
+    <label name="purchase_process_after"/>
+    <field name="purchase_process_after"/>
 </form>