The previous, manual calculation could be incorrect depending on
which SMS rates the free allowance was attributed to.
The new field also supersedes the old "letter_total" bolt-on so we
can get cost information consistently for both types.
This reverts 1b1839ad30, which removed
the usage from the dashboard because it was causing performance
problems:
> **The yearly usage section on the dashboard page takes too log as a
> result services with large yearly stats are timing out.**
>
> As a short term fix we have taken the yearly stats off the dashboard.
>
> There is a plan to create permanent statistic tables to warehouse the
> data.
The long term fix (the fact tables) is now in place, so it should be OK
to bring this back.
This is part of a wider piece of work to refresh the dashboard page now
that jobs are moving to their own page.
The diffDOM Javascript sometimes throws an error if it can’t calculate
a diff between the original content of the page and the updated HTML
delivered via AJAX. The problem seems to be when there’s not one,
consistent top-level element for it to base its calculations on.
This commit:
- makes sure that all AJAX-delivered partials have a wrapping `<div>`
- that this `<div>` has a consistent class name to make it clear why
it’s there
Previously the structure was
```
dashboard.html
|_ today.html
|_ some random html
|_ a few things split into partials
```
This commit simplifies the structure to just be:
```
dashboard.html
|_ partial
|_ partial
|_ …
```
