Give the user better error messages for CSV files

Makes uses of the additions to utils in https://github.com/alphagov/notifications-utils/pull/9

This commit strips out a lot of the complex stuff that the views and templates
in this app were doing. There is now a cleaner separation of concerns:

- utils returns the number and type of errors in the csv
- `get_errors_for_csv` helper in this app maps the number and type of errors
  onto human-friendly error messages
- the view and template just doing the glueing-together of all the pieces

This is (hopefully) easier to understand, definitely makes the component
parts easier to test in isolation, and makes it easier to give more specific
error messages.

app/utils.py

@@ -3,8 +3,6 @@ import re
 from functools import wraps
 from flask import (abort, session)
 
-from utils.process_csv import get_recipient_from_row, first_column_heading
-
 
 class BrowsableItem(object):
     """
@@ -43,3 +41,44 @@ def user_has_permissions(*permissions, or_=False):
                 abort(403)
         return wrap_func
     return wrap
+
+
+def get_errors_for_csv(recipients, template_type):
+
+    errors = []
+
+    missing_column_headers = list(recipients.missing_column_headers)
+
+    if len(missing_column_headers) == 1:
+        errors.append("add a column called ‘{}’".format("".join(missing_column_headers)))
+    elif len(missing_column_headers) == 2:
+        errors.append("add 2 columns, ‘{}’".format("’ and ‘".join(missing_column_headers)))
+    elif len(missing_column_headers) > 2:
+        errors.append(
+            "add columns called ‘{}’, and ‘{}’".format(
+                "’, ‘".join(missing_column_headers[0:-1]),
+                missing_column_headers[-1]
+            )
+        )
+
+    if recipients.rows_with_bad_recipients:
+        number_of_bad_recipients = len(list(recipients.rows_with_bad_recipients))
+        if 'sms' == template_type:
+            if 1 == number_of_bad_recipients:
+                errors.append("fix 1 phone number")
+            else:
+                errors.append("fix {} phone numbers".format(number_of_bad_recipients))
+        elif 'email' == template_type:
+            if 1 == number_of_bad_recipients:
+                errors.append("fix 1 email address")
+            else:
+                errors.append("fix {} email addresses".format(number_of_bad_recipients))
+
+    if recipients.rows_with_missing_data:
+        number_of_rows_with_missing_data = len(list(recipients.rows_with_missing_data))
+        if 1 == number_of_rows_with_missing_data:
+            errors.append("fill in 1 empty cell")
+        else:
+            errors.append("fill in {} empty cells".format(number_of_rows_with_missing_data))
+
+    return errors