We weren't checking if a service was in trial mode when they try to send
an uploaded file. If a service is in trial mode, we now show a banner at
the top of the preview page and no send button.
We now use the pattern of showing a box at the top of the page with the
error. The error message has a heading and can have additional details.
Error messages and the invalid pages get stored in the S3 metadata.
We had been storing whether or not a file was valid in the S3 metadata,
but using the query string of the URL to store the original filename
and the page count. This meant that if you tried to view the preview
letter page without the query string you would see a `500`. It was
possible for this to happen if you were signed out of Notify while on
the preview page - you would be redirected back to the preview page but
without the query string, causing an error.
Added a send button which only appears on the page if the query string
indicates that the PDF is valid. Before actually sending, we check that
the service has the right permissions and that the metadata for the
letter confirms the letter is valid (because the query string can be
changed).
This sanitises uploaded letters and stores the sanitised result in S3
with if it passes validation or the original PDF in S3 if validation
fails. A metadata value of 'status' is set to either 'valid' or
'invalid'.
Added a form to upload a single letter. Currently this only uses the
form to validate that a file is submitted and that the file is a PDF. If
either of these validations fail, the form will display an error.
Otherwise, we redirect to a new preview page which just has the filename
as the heading for now.
