Drafter.EventHandler (drafter v0.3.2)

Dispatches events to registered callback functions, in registration levels.

Handlers are kept as an ordered list of levels. Dispatch walks the levels from first to last, calls every handler in a level whose pattern matches, and stops as soon as a level contains a matching non-passthrough handler that returned :handled. Registration decides the order: :top puts a handler in a new first level, :bottom in a new last one, and {:after, pid} in a new level directly after the level containing that owner's handler.

Drafter.EventHandler.register_handler({:type, :key}, &handle/1, self())
Drafter.EventHandler.dispatch_event_sync({:key, :escape})
#=> :handled

Event patterns:

:any — every event
{:type, type} — any two-element event tuple tagged type
{type, sub_type} — a two-element event tuple tagged type whose payload is a map with type: sub_type, which is how a mouse sub-kind is selected

A handler function takes the event and returns :handled to consume it or anything else to let dispatch continue. Exceptions raised inside it are caught and turned into {:error, exception}, which does not count as handled.

Handlers are removed when their owner process exits; owners are monitored at registration. Dead owners are also swept on every dispatch.

The functions here resolve the handler process through Drafter.Session.Context under the :event_handler key, except register_handler/4 which accepts an explicit :target.

Summary

Functions

child_spec(init_arg)

Returns a specification to start this module under a supervisor.

dispatch_event(event)

Dispatch event without waiting for the handlers to run.

dispatch_event_sync(event)

Dispatch event and return once every handler that ran has returned.

register_handler(event_pattern, handler_fn, owner_pid, opts \\ [])

start_link(opts \\ [])

Start a handler process.

unregister_handler(owner_pid, event_pattern \\ nil)

Remove handlers owned by owner_pid.

Functions

child_spec(init_arg)

Returns a specification to start this module under a supervisor.

See Supervisor.

dispatch_event(event)

@spec dispatch_event(term()) :: :ok

Dispatch event without waiting for the handlers to run.

Returns :ok immediately and discards whether anything handled the event; use dispatch_event_sync/1 when that matters.

dispatch_event_sync(event)

@spec dispatch_event_sync(term()) :: :handled | :passthrough

Dispatch event and return once every handler that ran has returned.

:handled means a matching non-passthrough handler consumed the event and later levels were skipped. :passthrough means it was not consumed, whether or not handlers ran.

register_handler(event_pattern, handler_fn, owner_pid, opts \\ [])

@spec register_handler(term(), function(), pid(), keyword()) ::
  {:ok, pid()} | {:error, term()}

event_pattern is :any, {:type, type} or {type, sub_type}. handler_fn takes the event and returns :handled to consume it.

Options:

:passthrough — when true the handler never consumes the event, whatever it returns. Default false.
:level — :top (default) inserts a new first level, :bottom a new last one, {:after, pid} a new level right after the one holding pid's handler.
:target — the handler process to register with; defaults to the session's.

Returns {:ok, handler_process}, or {:error, :dead_process} if owner_pid is not alive. The registration is dropped when owner_pid exits.

start_link(opts \\ [])

@spec start_link(keyword()) :: GenServer.on_start()

Start a handler process.

Options:

:name — registered name, default Drafter.EventHandler. Pass nil to start it unregistered, which is what a session other than the local terminal does.

unregister_handler(owner_pid, event_pattern \\ nil)

@spec unregister_handler(pid(), term()) :: :ok

Remove handlers owned by owner_pid.

With event_pattern nil (the default) every handler that owner registered is removed and the monitor on it is released. With a pattern, only handlers registered under exactly that pattern are removed. Levels left empty are dropped.