[FIX+IMP] account_tax_balance:

* Tests
* PEP8
* Use invoice._convert_to_write(invoice._cache). This way, the onchange will be inheritable and will add here also the added values
* better get_context_values
* unify method compute_balance
* open move lines linked to balance

account_tax_balance/models/account_tax.py

@@ -2,7 +2,7 @@
 # © 2016 Lorenzo Battistini - Agile Business Group
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
 
-from openerp import models, fields
+from openerp import models, fields, api
 
 
 class AccountTax(models.Model):
@@ -13,31 +13,18 @@ class AccountTax(models.Model):
         string="Base Balance", compute="_compute_balance")
 
     def get_context_values(self):
-        if not self.env.context.get('from_date'):
-            from_date = fields.Date.context_today(self)
-        else:
-            from_date = self.env.context['from_date']
-        if not self.env.context.get('to_date'):
-            to_date = fields.Date.context_today(self)
-        else:
-            to_date = self.env.context['to_date']
-        if not self.env.context.get('target_move'):
-            target_move = 'posted'
-        else:
-            target_move = self.env.context['target_move']
-        if not self.env.context.get('company_id'):
-            company_id = self.env.user.company_id.id
-        else:
-            company_id = self.env.context['company_id']
-        return from_date, to_date, company_id, target_move
+        context = self.env.context
+        return (
+            context.get('from_date', fields.Date.context_today(self)),
+            context.get('to_date', fields.Date.context_today(self)),
+            context.get('company_id', self.env.user.company_id.id),
+            context.get('target_move', 'posted')
+        )
 
     def _compute_balance(self):
-        from_date, to_date, company_id, target_move = self.get_context_values()
         for tax in self:
-            tax.balance = tax.compute_balance(
-                from_date, to_date, company_id, target_move)
-            tax.base_balance = tax.compute_base_balance(
-                from_date, to_date, company_id, target_move)
+            tax.balance = tax.compute_balance(tax_or_base='tax')
+            tax.base_balance = tax.compute_balance(tax_or_base='base')
 
     def get_target_state_list(self, target_move="posted"):
         if target_move == 'posted':
@@ -48,39 +35,63 @@ class AccountTax(models.Model):
             state = []
         return state
 
-    def get_move_line_domain(self, from_date, to_date, company_id):
+    def get_move_line_partial_domain(self, from_date, to_date, company_id):
         return [
             ('date', '<=', to_date),
             ('date', '>=', from_date),
             ('company_id', '=', company_id),
         ]
 
-    def compute_balance(
-        self, from_date, to_date, company_id, target_move="posted"
-    ):
+    def compute_balance(self, tax_or_base='tax'):
         self.ensure_one()
-        move_line_model = self.env['account.move.line']
-        state_list = self.get_target_state_list(target_move)
-        domain = self.get_move_line_domain(from_date, to_date, company_id)
-        domain.extend([
-            ('move_id.state', 'in', state_list),
-            ('tax_line_id', '=', self.id),
-        ])
-        move_lines = move_line_model.search(domain)
-        total = sum([l.balance for l in move_lines])
+        move_lines = self.get_move_lines_domain(tax_or_base=tax_or_base)
+        # balance is debit - credit whereas on tax return you want to see what
+        # vat has to be paid so:
+        # VAT on sales (credit) - VAT on purchases (debit).
+        total = -sum([l.balance for l in move_lines])
         return total
 
-    def compute_base_balance(
-        self, from_date, to_date, company_id, target_move="posted"
-    ):
-        self.ensure_one()
-        move_line_model = self.env['account.move.line']
-        state_list = self.get_target_state_list(target_move)
-        domain = self.get_move_line_domain(from_date, to_date, company_id)
-        domain.extend([
+    def get_balance_domain(self, state_list):
+        return [
+            ('move_id.state', 'in', state_list),
+            ('tax_line_id', '=', self.id),
+        ]
+
+    def get_base_balance_domain(self, state_list):
+        return [
             ('move_id.state', 'in', state_list),
             ('tax_ids', 'in', self.id),
-        ])
-        move_lines = move_line_model.search(domain)
-        total = sum([l.balance for l in move_lines])
-        return total
+        ]
+
+    def get_move_lines_domain(self, tax_or_base='tax'):
+        move_line_model = self.env['account.move.line']
+        from_date, to_date, company_id, target_move = self.get_context_values()
+        state_list = self.get_target_state_list(target_move)
+        domain = self.get_move_line_partial_domain(
+            from_date, to_date, company_id)
+        balance_domain = []
+        if tax_or_base == 'tax':
+            balance_domain = self.get_balance_domain(state_list)
+        elif tax_or_base == 'base':
+            balance_domain = self.get_base_balance_domain(state_list)
+        domain.extend(balance_domain)
+        return move_line_model.search(domain)
+
+    def get_lines_action(self, tax_or_base='tax'):
+        move_lines = self.get_move_lines_domain(tax_or_base=tax_or_base)
+        move_line_ids = [l.id for l in move_lines]
+        action = self.env.ref('account.action_account_moves_all_tree')
+        vals = action.read()[0]
+        vals['context'] = {}
+        vals['domain'] = [('id', 'in', move_line_ids)]
+        return vals
+
+    @api.multi
+    def view_tax_lines(self):
+        self.ensure_one()
+        return self.get_lines_action(tax_or_base='tax')
+
+    @api.multi
+    def view_base_lines(self):
+        self.ensure_one()
+        return self.get_lines_action(tax_or_base='base')