Validate CSVs fully

This commit extends the existing function to validate each row’s phone number
to also validate that all the required data is present.

It does this using the checking that the `Template` class can do when given
a template and a `dict` of values.

app/utils.py

@@ -0,0 +1,70 @@
+class BrowsableItem(object):
+    """
+    Maps for the template browse-list.
+    """
+
+    def __init__(self, item, *args, **kwargs):
+        self._item = item
+        super(BrowsableItem, self).__init__()
+
+    @property
+    def title(self):
+        pass
+
+    @property
+    def link(self):
+        pass
+
+    @property
+    def hint(self):
+        pass
+
+    @property
+    def destructive(self):
+        pass
+
+
+class InvalidPhoneError(Exception):
+    def __init__(self, message):
+        self.message = message
+
+
+def validate_phone_number(number):
+    sanitised_number = number.replace('(', '')
+    sanitised_number = sanitised_number.replace(')', '')
+    sanitised_number = sanitised_number.replace(' ', '')
+    sanitised_number = sanitised_number.replace('-', '')
+
+    if sanitised_number.startswith('+'):
+        sanitised_number = sanitised_number[1:]
+
+    valid_prefixes = ['07', '447', '4407', '00447']
+    if not sum(sanitised_number.startswith(prefix) for prefix in valid_prefixes):
+        raise InvalidPhoneError('Must be a UK mobile number (eg 07700 900460)')
+
+    for digit in sanitised_number:
+        try:
+            int(digit)
+        except(ValueError):
+            raise InvalidPhoneError('Must not contain letters or symbols')
+
+    # Split number on first 7
+    sanitised_number = sanitised_number.split('7', 1)[1]
+
+    if len(sanitised_number) > 9:
+        raise InvalidPhoneError('Too many digits')
+
+    if len(sanitised_number) < 9:
+        raise InvalidPhoneError('Not enough digits')
+
+    return sanitised_number
+
+
+def format_phone_number(number):
+    import re
+    if len(number) > 9:
+        raise InvalidPhoneError('Too many digits')
+
+    if len(number) < 9:
+        raise InvalidPhoneError('Not enough digits')
+    return '+447{}{}{}'.format(*re.findall('...', number))