adding simple power form

rowers/models.py

@@ -4220,7 +4220,20 @@ class RowerExportForm(ModelForm):
         ]
 
 # Simple form to set rower's Functional Threshold Power
+class SimpleRowerPowerForm(ModelForm):
+    otwftp = forms.IntegerField(initial=0,required=False, label='FTP on water')
+    class Meta:
+        model = Rower
+        fields = ['ftp']
 
+    def __init__(self, *args, **kwargs):
+        super(SimpleRowerPowerForm, self).__init__(*args, **kwargs)
+        self.initial['otwftp'] = int((1-0.01*self.instance.otwslack)*self.instance.ftp)
+
+    def save(self, *args, **kwargs):
+        otwslack = -100.*(self.cleaned_data['otwftp']-self.cleaned_data['ftp'])/(self.cleaned_data['ftp'])
+        self.instance.otwslack = otwslack
+        return super(SimpleRowerPowerForm, self).save(*args, **kwargs)
 
 class RowerPowerForm(ModelForm):
     class Meta: