@spec configured_sessions(keyword() | map()) :: [FixAlchemy.SessionConfig.t()]

The sessions a connection config declares, in declaration order.

Delegates to FixAlchemy.SessionConfig.from_connection_config/1: a config listing sessions under :sessions gets those; one carrying the flat host/port/sender_comp_id and host_md/port_md/sender_comp_id_md groups instead gets the sessions :trading and :md those groups describe. Sessions that are not fully configured are dropped, so an empty list means the config names no usable session.

@spec default_config() :: map()

The baseline :fix backend config schema.

@spec default_fields() :: [map()]

The generic connection fields shared by every FIX backend.

@spec default_groups() :: [map()]

The sections a connection form lays its shared fields out in, in order.

Every field of default_fields/0 carries the :group it belongs to.

@spec default_session_group() :: map()

The repeatable session group of a connection form.

Each row is one FIX session: the fields it always carries, plus whichever shared settings it overrides. The overridable settings are not listed here — a form derives them from the backend's own :fields, taking every one that does not declare overridable: false, so a backend adding a shared field makes it overridable by the same act.

@spec get_active_account(binary()) :: {:ok, binary() | nil} | {:error, term()}

The account the connection's orders and account reads use.

@spec list_accounts(binary()) :: {:ok, [binary()]} | {:error, term()}

The accounts the connection's trading session holds.

Accounts come from the venue: whatever it named on the messages the session has received, in the order they were first seen. The :account a connection is configured with stands in while the venue has named none.

@spec overridable_fields([map()]) :: [map()]

The shared settings of fields a session may override, in declaration order.

Every field is overridable unless it declares overridable: false, which a backend uses for a setting that belongs to the connection as a whole rather than to any one session.

@spec prepare(keyword() | map()) :: :ok | {:error, term()}

Build what config needs before a session using it starts.

Generates and caches the dictionaries config names. Repeat calls reuse what is already built.

Returns {:error, reason} when a named dictionary cannot be built.

@spec set_active_account(binary(), binary()) :: :ok | {:error, term()}

Select the account the connection's orders and account reads use.

account must be one of list_accounts/1; any other is rejected with {:error, :unknown_account}. An order naming its own :account still goes to that one.

@spec with_client(binary(), (pid() -> result)) :: result | {:error, term()}
when result: term()

Run fun with the client of the session serving role.

The role is resolved through FixAlchemy.SessionDirectory, so a connection whose sessions are named anything at all is reached by what its sessions are for. with_client/2 uses the :trading role.

Returns {:error, :not_found} when the connection runs no session, {:error, {:no_session_for_role, role}} when none serves the role, and {:error, {:session_not_ready, name}} when the session that does has no live client.

@spec with_session(
  binary(),
  FixAlchemy.SessionConfig.role(),
  (FixAlchemy.SessionConfig.name() ->
     result)
) :: result | {:error, term()}
when result: term()

Run fun with the name of the session serving role.

Resolves as with_client/3 does, for callers addressing a session's subscriber processes rather than its client.