Adds a helper since there are only a few different parameters for
all BillingSession child clases, `build_support_url`.
Also, renames `get_support_url` to more explicitly note that it
is for realms: `get_realm_support_url`.
Use of `string_id` in the sponsorship request email content was
removed in commit d3834f8b9, but it is still used in the email
subject.
Updates the email subject to use the billing_entity_display_name,
which is still the Realm.string_id for Zulip Cloud organizations.
Sets this string as "billing_entity" in the context and subject
template.
This commit moves the 'update_license_ledger_if_needed' and its
helper function 'update_license_ledger_for_automanaged_plan'
to the 'BillingSession' abstract class.
This refactoring will help in minimizing duplicate code while
supporting both realm and remote_server customers.
Moves the 'update_license_ledger_for_manual_plan' function
to the 'BillingSession' abstract class.
This refactoring will help in minimizing duplicate code while
supporting both realm and remote_server customers.
Also adds `SWITCH_PLAN_TIER_AT_PLAN_END` for `CustomerPlan`
which will be used to mark status of remote server legacy
plans which are scheduled for an upgrade.
The logic for BillingSession.is_sponsored_or_pending would be the
same for all three child classes of BillingSession, so this should
be a method on the BillingSession abstract class.
Creates a process_support_view_request method for BillingSession
to process the various support requests that relate to the billing
system.
Moves approve_realm_sponsorship, update_realm_sponsorship_status,
and attach_discount_to_realm to this new BillingSession method.
Adds a new abstract property to BillingSession to have a string
value, billing_entity_display_name, to use for support messages
sent when these requests are processed.
The "send_invoice" and "charge_automatically" strings used by stripe
for the `collection_method` are referred to both as the "billing
method" and "billing modality" in the billing code.
Because we send this as data to stripe as either `collection_method`
or `billing_modality`, renames any references that are any form of
"billing method".
Updates do_change_plan_to_new_tier in BillingSession to use an
enum for the value returned when checking for a valid change
between two plan tier types. This makes it more explicit that
the implementation for a valid upgrade in plan tier will be
different from a valid downgrade in plan tier.