[REF] refactor the code in order to split it in several file

mail_usability/wizard/email_template_preview.py

@@ -0,0 +1,44 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 Akretion (http://www.akretion.com).
+# @author Sébastien BEAU <sebastien.beau@akretion.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from openerp import api, fields, models
+
+
+class TemplatePreview(models.TransientModel):
+    _inherit = "email_template.preview"
+
+    res_id = fields.Integer(compute='_compute_res_id')
+    object_id = fields.Reference(selection='_reference_models')
+
+    @api.model
+    def default_get(self, fields):
+        result = super(TemplatePreview, self).default_get(fields)
+        if result.get('model_id'):
+            model = self.env['ir.model'].browse(result['model_id'])
+            result['object_id'] = model.model
+        return result
+
+    def _reference_models(self):
+        result = self.default_get(['model_id'])
+        if result.get('model_id'):
+            model = self.env['ir.model'].browse(result['model_id'])
+            return [(model.model, model.name)]
+        else:
+            models = self.env['ir.model'].search([('state', '!=', 'manual')])
+            return [(model.model, model.name)
+                    for model in models
+                    if not model.model.startswith('ir.')]
+
+    @api.depends('object_id')
+    def _compute_res_id(self):
+        for record in self:
+            if self.object_id:
+                record.res_id = self.object_id.id
+
+    def send(self):
+        template = self.env['mail.template'].browse(
+            self._context['template_id'])
+        template.send_mail(
+            self.res_id, force_send=True, raise_exception=True)